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#369704 - 03/11/2017 04:30 BlueGigaEmpeg
tfabris
carpal tunnel

Registered: 20/12/1999
Posts: 30784
Loc: Seattle, WA
Current status of project:



Sorry that I had the volume turned way down on the music, so you can barely hear the songs playing. Audio is quite good in general.

Existing bugs:

- Empeg serial notifications don't always notify when unpausing the player from the player's own front panel. Though everything works, sometimes the car's touchscreen will display that the player is paused even when it is playing.

- Empeg serial notifications do not include Album name, only track title, artist, and genre.

- Empeg serial notifications can sometimes stomp on themselves, causing parsing errors. Example: Quickly switching tracks on the empeg's front panel with the next/prev buttons can sometimes make a new notification message appear right in the middle of the message that would otherwise be sending one of the track titles. So sometimes if you switch tracks really fast on the empeg's front panel, it will occasionaly "miss" getting the new track info for the current track.

- Now that I'm powering this thing with its own power supply so that both the empeg and the BlueGiga are getting their power from the same 12v source, I have a small (faint) amount of ground loop noise. It's nearly inaudible but it's bugging me and I'm trying to get rid of it completely by fiddling with the routing on the development prototype.

Next step:

- PCB for sandwiching the Arduino to the BlueGiga board, mounting in a nice box, perhaps 3D printing a custom box.

- Actually mount the empeg in the trunk, with the remote display up front via the long ribbon cable.
_________________________
Tony Fabris

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#369705 - 03/11/2017 04:35 Re: BlueGigaEmpeg [Re: tfabris]
tfabris
carpal tunnel

Registered: 20/12/1999
Posts: 30784
Loc: Seattle, WA
Also, I've just now updated my example code here with the latest code demonstrated in that video:

https://create.arduino.cc/editor/tfabris/4c5eea9a-1462-45d7-908d-81a5bb6b0d90/preview
_________________________
Tony Fabris

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#369707 - 03/11/2017 13:18 Re: BlueGigaEmpeg [Re: tfabris]
mlord
carpal tunnel

Registered: 29/08/2000
Posts: 13628
Loc: Canada
So.. now that you've rolled your own RS232 level converters, perhaps think about using that to interface the BT board directly to the empeg, rather than having an extra processor (Arduino) in the middle?

I expect to catch up to you within a few weeks perhaps, using such a setup, blatantly stealing ..re-using.. your code/ideas to run directly on the empeg. smile

Pretty awesome demo, by the way!!

EDIT:
I'm not sure that the empeg really has the concept of an "Album" (or does it?). It knows about "playlists" though, and those have names which could be made available.

If the pause/play status is being lost somehow, you can still detect it in your middleman by noting that the timecodes either stop or stop increasing.



Edited by mlord (03/11/2017 13:42)

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#369709 - 03/11/2017 13:58 Re: BlueGigaEmpeg [Re: tfabris]
mlord
carpal tunnel

Registered: 29/08/2000
Posts: 13628
Loc: Canada
Now that there's a DKWT32i dev board in front of me, I finally appreciate just how tiny the actual WT32i BT module is. And it really needs hardly nothing to hook it up directly to something like an empeg.

I'm thinking of perhaps using the empeg tuner serial port for it, to remove the need for RS232 level conversions -- would still need to deal with 5V vs. 3.3V logic there, but that's much simpler than adding a MAX chip and stuff. And using the tuner port removes all conflicts with the main empeg serial port, freeing that up for debugging/programming purposes.

If the WT32i board were mounted inside the empeg, say onto a drive bay, then it could draw power from the empeg itself, and even use digital audio input (I2S) from the empeg (no hum!).

There is the small issue of a low powered RF device tucked inside an all-metal shell, but that could be dealt with in a number of ways. Eg. a replacement empeg lid made of a different material, or perhaps just a strategically located hole in the lid.

EDIT: The tuner serial port is available outside of the empeg as well, so it could be used regardless. I'll probably start with that and see how things go. And I'll use the 12V output from the empeg to the tuner as the source for powering the BT module.

For now, I'll just use a MAX chip to the main empeg serial port and try get Tony's stuff replicated inside the empeg.




Edited by mlord (03/11/2017 14:22)

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#369714 - 03/11/2017 18:48 Re: BlueGigaEmpeg [Re: mlord]
tfabris
carpal tunnel

Registered: 20/12/1999
Posts: 30784
Loc: Seattle, WA
Thanks, Mark!

You make a lot of excellent points!


Quote:
I expect to catch up to you within a few weeks perhaps, using such a setup, blatantly stealing ..re-using.. your code/ideas to run directly on the empeg.


It's not stealing if I *want* you to take it. smile Of course, you're going to have to rewrite it significantly to get it working on the empeg. There are some things you'd have to do quite differently on the empeg.

I'm really hoping that you'll catch up and surpass me, so that either one or both of us are successful. I can envision either you completing something that works before I finish mine, and I just drop what I'm doing and use your project instead, or I get my project working well now, use it for a little while, and then eventually switch to using yours later.


Quote:
So.. now that you've rolled your own RS232 level converters, perhaps think about using that to interface the BT board directly to the empeg, rather than having an extra processor (Arduino) in the middle?


I clearly see the advantage to doing it that way. To be successful at that, I'd need to level up in a couple of areas that I don't have enough experience in right now: Code development on the empeg itself, and the necessary EE knowledge to get the bluetooth chip working directly on my own board. Both would require that I get outside help that's a little bit higher level than what I've had so far. Right now, the solution I'm building is within my power to complete soon, and I'd like to try to get that working first, even if only for better debugging the code and understanding all the bluetooth communication tricks. In any case, whenever you get something working with your method, I'm happy to take your design and your code and roll with it.


Quote:
I'm not sure that the empeg really has the concept of an "Album" (or does it?). It knows about "playlists" though, and those have names which could be made available.


Yes, the empeg has a field for the album name and displays the album name on its screen just fine. That's just one of the fields that wasn't included in the serial port output at the moment.


Quote:
If the pause/play status is being lost somehow, you can still detect it in your middleman by noting that the timecodes either stop or stop increasing.


Indeed! I thought about doing just that very thing as soon as I saw the root cause of the issue. However there is a problem with doing it that way: If you are fast-forwarding or rewinding when the player is paused (something that it possible to do on the empeg from its front panel), then it might falsely tell the host stereo that it's playing when it's actually not. Still, that might be better than what it's currently doing.

By the way, that's another bug in the current code: It does not implement fast forward and rewind from the car's front panel or steering wheel controls. This is because my car doesn't do that and so I have no testbed that implements the feature to get that working. My car is weird in this regard. It has several things where you might expect FF/REW to work, and it simply doesn't work this way at all. There are no independent buttons for FF/REW, and holding down the Next/Prev buttons does nothing in most cases. What's interesting is that it does implement FF/REW in one particular specific case, but its absence in other cases is puzzling:

- Honda stereo connect to smartphone with bluetooth to play music: No FF/REW.
- Honda stereo connect to smartphone in "iPod" mode via USB cable: No FF/REW.
- Honda stereo built-in CD player (this is where I expect it to work most): No FF/REW.
- Honda stereo connect to iPhone Apple Car Play with USB cable: FF/REW works.

The bluetooth AVRCP commands that I receive from the module have a "button down" and "button up" message (a press and a release) so you'd think that I could implement it by having my own code detect the time span between AVRCP PLAY PRESS and AVRCP PLAY RELEASE commands. You'd think that. But the Honda stereo doesn't split them out. If you hold the button on the Honda stereo, it waits until you release the button then sends both of those messages simultaneously after your release. Sigh.


Quote:
I finally appreciate just how tiny the actual WT32i BT module is. And it really needs hardly nothing to hook it up directly to something like an empeg.


Like what? I haven't been able to decipher all the specs on the datasheet yet. It's a lot of information to get through.



Quote:
If the WT32i board were mounted inside the empeg, say onto a drive bay, then it could draw power from the empeg itself, and even use digital audio input (I2S) from the empeg (no hum!).


Yes yes yes! This! I have thought about this many times as I have been working on this. I have no idea where to even begin implementing something like this. Stu might know. smile I wonder if it's as simple as connecting some wires from the empeg to the I2S inputs on the BlueGiga chip, or if a ton of circuitry is needed? That BlueGiga dev board has a ton of digital audio interface pins.


Quote:
There is the small issue of a low powered RF device tucked inside an all-metal shell, but that could be dealt with in a number of ways. Eg. a replacement empeg lid made of a different material, or perhaps just a strategically located hole in the lid.


I wonder if it would "Just Work". The empeg shell isn't a proper faraday cage to begin with, is it? And the BlueGiga chip has a really decent range (I tested it out to be approx the width of my entire house the other day) so maybe having it in the car trunk inside the empeg would be fine? Dunno.

The other option is an external antenna of course. The chip has provision for that, I'm sure. Run it out the back somewhere. Perhaps replace one of the pins on the dock connector that you won't be using any more, such as the cell phone mute wire (won't be needing that wire any more since the bluetooth handles all the cell phone muting now).

Anyway, exciting times!

Thanks Mark, and to everyone else on the BBS, who has been offering tips and answering questions as I go along with this project. You've all been so great!
_________________________
Tony Fabris

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#369715 - 03/11/2017 19:10 Re: BlueGigaEmpeg [Re: tfabris]
tfabris
carpal tunnel

Registered: 20/12/1999
Posts: 30784
Loc: Seattle, WA
Mark,

I've got a question about how you intend to develop the code for this on the empeg... This is probably me not understanding how that kind of development works...

While developing on the Arduino, I needed three serial ports:

1. The serial port that talks to the empeg.
2. The serial port that talks to the bluetooth chip.
3. The debug/monitoring/command-issuing serial port (in my case, via the Arduino USB port).

The empeg doesn't have that many serial ports. How would one do the debugging and monitoring during development on the empeg?
_________________________
Tony Fabris

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#369716 - 03/11/2017 20:03 Re: BlueGigaEmpeg [Re: tfabris]
mlord
carpal tunnel

Registered: 29/08/2000
Posts: 13628
Loc: Canada
Okay, this is just so exciting! smile
I'm writing empeg code again!

Okay, so not very quickly, but I remembered how to cross-compile programs for the empeg, so it's a start anyway.

I wrote a modest program to talk to the BT adapter whilst it is connected to the serial port. This part, I actually just did on my (Linux) notebook, and tested/debugged it all there. Then I recompiled it for the empeg, FTP'd it over, and it works there too.

Happy Days!
smile smile smile

My plan is to continue development/testing on the laptop as much as possible, because it is quicker and more accessible than the empeg. Then once in a while bump the program back over to the empeg just to make sure it's all still good.

This could be quick, or a very long time. So don't wait around for me, Tony: you have been doing an excellent job serving yourself (and I) here, so please keep on doing so.

Long term, when(if) this gets close to parity with Tony, I think we both might agree that the Arduino is redundant: running on the empeg gives better access to more features. Eg. "Album Titles", or possibly even browsing the empeg playlists from a cooperating head unit.

I do plan to do this, but.. I have lots of plans, and so.. don't wait for me.

Cheers

EDIT: Note to self: When working from the laptop, don't use the built-in USB-UART of the Dev board, as it suffers badly from buffer bloat and consequently loses data if I so much as sneeze. Instead, use either the built-in serial port on the laptop, or a USB-serial adapter, connecting to the RX/TX pins on the board through a MAX chip.



Edited by mlord (03/11/2017 20:11)

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#369717 - 03/11/2017 20:16 Re: BlueGigaEmpeg [Re: tfabris]
mlord
carpal tunnel

Registered: 29/08/2000
Posts: 13628
Loc: Canada
Originally Posted By: tfabris
The empeg doesn't have that many serial ports. How would one do the debugging and monitoring during development on the empeg?


I am doing most of the debugging on a laptop, so the code pretty much "just works" when flipped over to the empeg.

But.. the empeg, courtesy of Hijack, has a very large number of things resembling serial ports for debug purposes: telnet sessions.

So I just telnet into the empeg over ethernet to run/debug there when needed. stdout/stderr/stdin are all directed to the telnet session when running code such as this. The serial port has to be opened manually: /dev/ttyS1

So you need one serial port for the BT board. And a telnet session for debugging. No need for a third one (the code is already on the empeg). Use /proc/empeg_notify for player status/state -- some enhancements required and forthcoming!

For player commands, I forget exactly how, but there is a way to inject those to the player even when "Apps use Serial Port" is enabled.



Edited by mlord (03/11/2017 20:21)

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#369718 - 03/11/2017 20:26 Re: BlueGigaEmpeg [Re: mlord]
tfabris
carpal tunnel

Registered: 20/12/1999
Posts: 30784
Loc: Seattle, WA
Originally Posted By: mlord
I think we both might agree that the Arduino is redundant: running on the empeg gives better access to more features. Eg. "Album Titles"


Totally agreed. The Arduino is in the mix right now merely because I have experience with it, it's an easy coding environment, and there is a lot of handholding with a ton of reference material on the internet, and I can iterate quickly on it.

Quote:
or possibly even browsing the empeg playlists from a cooperating head unit.


Oh wow yes. There is a detailed specification for the BlueGiga chip on how to handle that kind of thing. It's all detailed in this document and it's quite complicated, but I think it's do-able.

I know that my car head unit has a "music search" option but I think it only was implemented in iOS Apple CarPlay mode and/or Android Auto mode. I haven't looked closely to see if it's implemented in Bluetooth mode or not, but I know the chip at least supports it.

Quote:
Note to self: When working from the laptop, don't use the built-in USB-UART of the Dev board, as it suffers badly from buffer bloat and consequently loses data if I so much as sneeze. Instead, use either the built-in serial port on the laptop, or a USB-serial adapter, connecting to the RX/TX pins on the board through a MAX chip.


Interesting. The only time I ever used that port on the dev board was to use it to install the latest firmware onto the BlueGiga chip. By the way, if you encounter problems with the functionality of my code, you might want to make sure you've updated your BlueGiga chip to the latest firmware to make sure that we're all talking to the same back end code. I don't know how much has changed in the command set from version to version. Instructions for updating the firmware are in the code comments at the top of my example code.

Just realized: One other note that I foresee being a potential problem with my example code. When the host stereo queries for track titles and other metadata, it could do it in one of two possible ways:
1. Separate queries for each individual piece of metadata, i.e., one query for Title, another query for Artist, another for Genre, etc.
2. A single query for multiple combinations of the metadata, such as querying for all of them, or a subset of them, all at once with a single query statement.

I have noticed that there is support in the BlueGiga command set for both of those methods. I noticed that my Honda only ever uses the "one at a time" query method (though it does query for all of them in quick succession), so my code only knows how to answer that type of "one at a time" individual query. I have not implemented parsing and response of the second "all at once" query method, since that's more complicated code-wise and I don't have a device which performs that kind of query to test it against. Your car stereo might possibly implement that latter query type, so you might have to implement a parser and a response method for it. Keep an eye out for that.

_________________________
Tony Fabris

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#369719 - 03/11/2017 21:02 Re: BlueGigaEmpeg [Re: tfabris]
tfabris
carpal tunnel

Registered: 20/12/1999
Posts: 30784
Loc: Seattle, WA
Also, I'm investigating how to get rid of the last little bit of ground loop noise, and I'm thinking of trying out an isolated power supply.

Right now I'm using one of these:
https://www.pololu.com/product/2851

And I'm thinking of switching to one of these:
https://www.digikey.com/product-detail/e...81-5-ND/2242601

What do you guys think? Would that power supply at least work in my prototype?
_________________________
Tony Fabris

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#369720 - 03/11/2017 21:24 Re: BlueGigaEmpeg [Re: tfabris]
mlord
carpal tunnel

Registered: 29/08/2000
Posts: 13628
Loc: Canada
Yeah, thanks for the easy firmware update instructions. I used my work laptop to do that earlier today.

I've been poking around Hijack and the empeg more, gradually remembering how the serial port stuff all works. It looks like some surgery is needed there to enable full use of the serial port for the BT module. Currently, any input from the BT goes right to the player, causing all kinds of weird things to happen at high speed. smile

I think I'll create a special fake serial device, and redirect everything for the player to that on startup, when directed so by a suitable config.ini entry (eg. btmode=1). That would get the player completely out of the way, while still being able to capture its output (for /proc/empeg_notify), as well as still being able to inject commands back into it.

I wonder if anyone out there is still using "apps" on the empeg? Probably, so will try and keep that working. The code will get a bit messier than necessary for that, but c'est la vie.


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#369721 - 03/11/2017 21:54 Re: BlueGigaEmpeg [Re: tfabris]
mlord
carpal tunnel

Registered: 29/08/2000
Posts: 13628
Loc: Canada
Originally Posted By: tfabris
Also, I'm investigating how to get rid of the last little bit of ground loop noise, and I'm thinking of trying out an isolated power supply.

Right now I'm using one of these:
https://www.pololu.com/product/2851

And I'm thinking of switching to one of these:
https://www.digikey.com/product-detail/e...81-5-ND/2242601

What do you guys think? Would that power supply at least work in my prototype?


Looks very expensive.
Which audio output are you noting the noise on, the Home-mode RCA jacks, or the car-mode outputs: docking connector jacks? or Home-Dock jacks?

The docking-connector jacks appear to have isolated signal grounds, whereas the RCA jacks use the main earth/chassis ground. I think.

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#369722 - 03/11/2017 22:04 Re: BlueGigaEmpeg [Re: mlord]
tfabris
carpal tunnel

Registered: 20/12/1999
Posts: 30784
Loc: Seattle, WA
Originally Posted By: mlord
Looks very expensive.


Yes, true, but do you think it will work at all? In other words, do you think that part that I linked will successfully take the car 12v power as it source, and correctly output 5v that the Arudino and the Bluegiga can run off of?

Quote:
Which audio output are you noting the noise on, the Home-mode RCA jacks, or the car-mode outputs: docking connector jacks? or Home-Dock jacks? The docking-connector jacks appear to have isolated signal grounds, whereas the RCA jacks use the main earth/chassis ground. I think.


All of the above. I'm hoping that it's noise from the power supply specifically, and not anything the empeg's audio outputs are responsible for.

The reason I'm thinking that it's the power supply is because I don't have any noise as long as I am powering the arduino and the BlueGiga board from a separate 5v power supply that is not the same power source as the Empeg, i.e., the empeg gets its power from either the car 12v or a home AC adapter, while the arduino+blueGiga get their power from the USB port of my laptop in battery power mode. As soon as I power them all off the same 12v supply (the empeg directly off the supply and the Arduino/BlueGiga off of the pololu 5v converter off of the same supply), then the noise appears. So I'm hoping that an isolated power supply will do the trick.
_________________________
Tony Fabris

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#369723 - 03/11/2017 22:10 Re: BlueGigaEmpeg [Re: tfabris]
mlord
carpal tunnel

Registered: 29/08/2000
Posts: 13628
Loc: Canada
Sure, okay. But the "12v suppy" for the empeg is the Honda, right? Does it have the noise there?

If this is just an in-home thing, then no biggie, right.


Edited by mlord (03/11/2017 22:10)

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#369725 - 04/11/2017 02:49 Re: BlueGigaEmpeg [Re: mlord]
tfabris
carpal tunnel

Registered: 20/12/1999
Posts: 30784
Loc: Seattle, WA
Excellent question about where the power is coming from.

I am testing in the following conditions. There's enough variables to make this list kind of big, so I'm PRETTY sure about all of these, but not 110 percent sure:

- Empeg powered by AC Adapter, Arudino+BlueGiga powered by laptop USB port on laptop battery: No noise.

- Empeg powered by AC Adapter, Arudino+BlueGiga powered by laptop USB port with laptop plugged into AC power: No noise.

- Empeg powered by Car 12v from Cig Lighter adapter into Empeg Home 5.5mm barrel plug, Arudino+BlueGiga powered by laptop USB port on laptop battery: No noise.

- Empeg powered by Car 12v from Cig Lighter adapter into Empeg Docking Sled power wires, Arudino+BlueGiga powered by laptop USB port on laptop battery: No noise.

- Empeg powered by AC Adapter, Arudino+BlueGiga powered by the same AC adapter through the Pololu 5v power supply: Small amount of noise.

- Empeg powered by Car 12v from Cig Lighter adapter into Empeg Home 5.5mm barrel plug, Arudino+BlueGiga powered by the same Cig Lighter adapter through the Pololu 5v power supply: Small amount of noise.

- Empeg powered by Car 12v from Cig Lighter adapter into Empeg Docking Sled power wires, Arudino+BlueGiga powered by the same Cig Lighter adapter through the Pololu 5v power supply: Small amount of noise.
_________________________
Tony Fabris

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#369726 - 04/11/2017 07:41 Re: BlueGigaEmpeg [Re: tfabris]
tfabris
carpal tunnel

Registered: 20/12/1999
Posts: 30784
Loc: Seattle, WA
Example code updated again at https://create.arduino.cc/editor/tfabris/4c5eea9a-1462-45d7-908d-81a5bb6b0d90/preview

Mostly just a pass through the code comments to clean them up and bring them inline with the project's current state.
_________________________
Tony Fabris

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#369727 - 04/11/2017 14:16 Re: BlueGigaEmpeg [Re: tfabris]
mlord
carpal tunnel

Registered: 29/08/2000
Posts: 13628
Loc: Canada
Thank-you for the frequent code updates!

For the noise, my theory is that perhaps the hard drive motor(s) of the empeg are back feeding some noise. Feel free to blow away this theory by stating you are using SSDs (or CFs) instead of mechanical drives! smile

Somebody really clever (like Patrick or some others on the BBS) could probably point out a simple array of capacitor values to use to filter out such unwanted noise. Eg. my untrained mind might attempt just stuffing all of these in parallel across the 12V/GND lines in front of the BT power supply: 1000uF 100uF 10uF 1uF 0.1uF 0.01uF. But then I have bins on hand here with all of those. smile

I wonder if it might help to instead draw 12V source power for the BT board from the 12V on the tuner connector?



Edited by mlord (04/11/2017 14:18)

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#369728 - 04/11/2017 16:28 Re: BlueGigaEmpeg [Re: mlord]
tfabris
carpal tunnel

Registered: 20/12/1999
Posts: 30784
Loc: Seattle, WA
I did switch to an SSD recently. smile

I do a have bin of capacitors here that I could try bridging the 12v/Gnd line, I'll see if that works. I could also try drawing the power from the tuner connector as well, that's a good suggestion!
_________________________
Tony Fabris

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#369729 - 04/11/2017 16:38 Re: BlueGigaEmpeg [Re: mlord]
tfabris
carpal tunnel

Registered: 20/12/1999
Posts: 30784
Loc: Seattle, WA
Going back to the debug question...

Originally Posted By: mlord
So I just telnet into the empeg over ethernet to run/debug there when needed. stdout/stderr/stdin are all directed to the telnet session when running code such as this. The serial port has to be opened manually: /dev/ttyS1


So, in my Arduino code, there is a place in the code that reads input from the serial port connected to the BlueGiga chip. In addition to processing those characters, it also echoes those characters to the Arduino's debug/monitor serial port. And anything I type into the debug/monitor serial port, conversely, is echoed to the serial port connected to the BlueGiga chip, so that I can issue commands directly to test them out.

The corresponding version of that for coding on the empeg itself would be that any characters received from /dev/ttyS1 would be echoed to ... what? dev/tty<something else>?
_________________________
Tony Fabris

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#369730 - 04/11/2017 16:46 Re: BlueGigaEmpeg [Re: mlord]
tfabris
carpal tunnel

Registered: 20/12/1999
Posts: 30784
Loc: Seattle, WA
And speaking of the tuner connector...

When the tuner module sends its audio data back to the empeg so that it can output the audio to the speakers, does it do so as analog or as digital?

In other words, in addition to a second serial port existing on the tuner connector, is there by happenstance an unused digital audio connection of some kind on that tuner connector? And if so, does it have the potential to be a two-way digital interface, receiving digital audio from the player instead of sending digital audio to the player?
_________________________
Tony Fabris

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#369731 - 04/11/2017 17:15 Re: BlueGigaEmpeg [Re: tfabris]
mlord
carpal tunnel

Registered: 29/08/2000
Posts: 13628
Loc: Canada
Originally Posted By: tfabris
When the tuner module sends its audio data back to the empeg so that it can output the audio to the speakers, does it do so as analog or as digital?


It appears as some weird analog multiplexed thing, for which the empeg DSP includes special processing to extract L/R audio from. Those pins on the DSP appear to be single purpose: strictly expecting an FM Level as input (or an AM Level).

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#369732 - 04/11/2017 17:17 Re: BlueGigaEmpeg [Re: tfabris]
mlord
carpal tunnel

Registered: 29/08/2000
Posts: 13628
Loc: Canada
Originally Posted By: tfabris
The corresponding version of that for coding on the empeg itself would be that any characters received from /dev/ttyS1 would be echoed to ...


Standard Output (stdout). Aka. File Descriptor number 1. Aka. The default destination of printf() or putchar(). This is open and available on program startup, without the need to explicitly open() it, and normally maps to whatever "terminal" (tty) session (serial, ssh, telnet, an xterm window, etc..) from which the program was launched.

So, like this:
Code:

int read_and_echo (void)
{
        char c;
        int fd = open("/dev/ttyS1", O_RDWR);

        if (fd == -1) {
                perror("/dev/ttyS1");
                exit(1);
        }

        while (1 == read(fd, &c, 1)) {
                putchar(c);  /* stdout: could be anything, and we don't care! */
                fflush(stdout);
        }
        close(fd);
}


Edited by mlord (04/11/2017 17:38)

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#369733 - 04/11/2017 17:30 Re: BlueGigaEmpeg [Re: mlord]
mlord
carpal tunnel

Registered: 29/08/2000
Posts: 13628
Loc: Canada
In the case of a telnet session, here is where the kernel (Hijack) sets this up in ktelnetd:
Code:

        // set up stdin,stdout,stderr to all point at the socket
        sockfd = get_fd(parms->clientsock->inode);  /* 0: stdin */
        dup(sockfd);   /* 1: stdout */
        dup(sockfd);   /* 2: stderr */


So in this case, stdout/stderr (and stdin for reading) point at the "socket", which is a handle for the remote connection (the telnet client running on a PC).

The important bit is that the program itself doesn't need to know this. It just reads stuff from stdin, and writes stuff to stdout (and/or stderr). And it all works. Whether running locally on a serial port, in a window on a desktop GUI, or at the end of some remote network connection (ssh, telnet.. ).

EDIT: So, while we're on this topic: Anything that has been "opened" on a Linux system has a file descriptor associated with it. A file descriptor is what you get back from calling open(). Or socket().

These begin with 0 for the first thing opened, and each new thing gets the lowest number that is not currently in use. So stdin=0, stdout=1, stderr=2 .. is the most commonly seen order, though it is not guaranteed to look like that.

The numbers are simply indexes into a kernel table describing each open "object" and the state of reading/writing on that object. Aka. the File Descriptor table. There is a unique file descriptor table for each process.

In the /proc/ directory on Linux (including the empeg), there is a subdirectory for each process, as well as one called "self" for the current running program. If you telnet to the empeg, and do cd /proc/self, you will see a lower level subdirectory called fd. This is a view of the process's file descriptor table. Look into it like this: ls -lF /proc/self/fd/
Code:
ls -lF /proc/self/fd/

total 0
lrwx------    1 0        0              64 Aug  3 12:07 0 -> socket:[8]
lrwx------    1 0        0              64 Aug  3 12:07 1 -> socket:[8]
lrwx------    1 0        0              64 Aug  3 12:07 2 -> socket:[8]
lrwx------    1 0        0              64 Aug  3 12:07 255 -> socket:[8]

Doing the same thing when logged in via the serial port gives this instead:
Code:
ls -lF /proc/self/fd/

total 0
lrwx------    1 0        0              64 Aug  3 12:12 0 -> /dev/ttyS1
lrwx------    1 0        0              64 Aug  3 12:12 1 -> /dev/ttyS1
lrwx------    1 0        0              64 Aug  3 12:12 2 -> /dev/ttyS1
lr-x------    1 0        0              64 Aug  3 12:12 3 -> /proc/35/fd/


Note that the fourth entry in the second case is the file descriptor for reading from /proc/self/fd/ at that point in time, when "self" was process id (PID) number 35.

Some fun, huh!


Edited by mlord (04/11/2017 18:06)

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#369738 - 05/11/2017 22:34 Re: BlueGigaEmpeg [Re: mlord]
tfabris
carpal tunnel

Registered: 20/12/1999
Posts: 30784
Loc: Seattle, WA
Thanks very much for the tutorial about how stdout/stdin/stderr works on linux, that will be very useful to me if/when I start digging into this in the "everything on the empeg" mode at some point. It is also good general knowledge to have about linux coding.

In other news, I have updated the example code here:
https://create.arduino.cc/editor/tfabris/4c5eea9a-1462-45d7-908d-81a5bb6b0d90/preview
(I'm considering making a GitHub for it instead, that kinda makes more sense, maybe I'll get around to that soon).

Changes in the most recent version:

- Some more code comment cleanup.

- Implemented your suggestion about making the playback state change if it detects that the track timestamp has been changing recently. It does indeed do the thing I feared: Making it look like the track is playing if you FF while the track is paused. But this is not a big deal and is better than the alternative.

- Implemented fast forward and rewind for car stereo headunits that support FF/REW over Bluetooth. My Honda factory stereo doesn't, but my roommate's aftermarket Kenwood stereo does, so I was able to get something working in that area.

- More details about track playback position indication are now in the code.


In other news:

I realized that my roommate's car stereo was an aftermarket Kenwood unit with a bluetooth input and track titles on the screen. So I could test out my code with a second stereo finally!

To my surprise, almost everything worked correctly. And his stereo can do FF/REW over bluetooth (something my Honda inexplicably refuses to do at all) and so I was able to implement FF/REW in the code now.

However there is one interesting thing about his stereo that is different from my Honda. And it's a pretty big bug that I am stumped by and now I need to know how to fix. Googling for it isn't helping yet, so I'm not sure about how to handle this. Here's the issue...

The bluetooth code depends upon the host car stereo headunit to query us for the track metadata. In other words, we can't "push" track titles up to the car stereo screen until the car stereo asks us for them. They are implemented only as a response to the query.

I have been using the following command, sending this up to the car stereo to make it turn around and re-query us for the new track titles. This command works on the Honda stereo:

Code:
      SendBlueGigaCommand(F("AVRCP NFY CHANGED 1 2 1"));  
      // Where:
      //      AVRCP NFY   - The notification command to send to the head unit.
      //      CHANGED     - Indicate to the head unit that there was a change to the track.
      //      1           - Send this message with transaction label 1 (an arbitrary sequence number).
      //      2           - The notification message we will send contains event ID 2, which is "TRACK_CHANGED".
      //      1           - The sole parameter value for the TRACK_CHANGED, with a "1" indicating that there is indeed a track selected.


When I issue that command to the bluetooth chip when it is paired with the Honda stereo, it responds instantly and re-queries for new track metadata. Unfortunately, on the Kenwood unit, the command does nothing and the Kenwood unit doesn't re-query for new track metadata.

I know that sometimes the Kenwood unit successfully queries for track data. Immediately after first connection to the bluetooth chip, it does query for the track information and my code responds as expected. The track titles appear on the screen of the Kenwood, and all is well. Then when I go to change to another track on the Empeg, and it issues the "AVRCP NFY CHANGED 1 2 1", nothing happens, and the Kenwood keep displaying the same song title, though now a different song is coming out of the speakers.

I know that there must be a standardized way to make this work, because all the cell phones that we pair up with this Kenwood unit correctly display track titles when tracks get changed. But I don't know how to sniff their communications to find out how this is done.

Anyone have any ideas of how to kick the headunit to make it re-query for new track metadata?
_________________________
Tony Fabris

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#369739 - 05/11/2017 23:11 Re: BlueGigaEmpeg [Re: tfabris]
mlord
carpal tunnel

Registered: 29/08/2000
Posts: 13628
Loc: Canada
Originally Posted By: tfabris
I don't know how to sniff their communications to find out how this is done.


For an Android handset, enable Developer Mode, and then go to Settings --> Developer options --> Enable Bluetooth HCI snoop log. Stuff should then be written to /sdcard/Android/data/btsnoop_hci.log which one can pull off later and feed into Wireshark (on a PC) for analysis.

I have not actually tried this, but others have. The exact pathname may vary, but the file itself is always called btsnoop_hci.log


Edited by mlord (05/11/2017 23:14)

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#369740 - 06/11/2017 00:35 Re: BlueGigaEmpeg [Re: mlord]
tfabris
carpal tunnel

Registered: 20/12/1999
Posts: 30784
Loc: Seattle, WA
Cool, I should be able to do that. I don't have an android phone but others in my household do, and that might give really interesting information.

In the meantime, I have a suspicion about what might have caused it. Looking at my own transaction logs from the session, I see that there was a moment during the first query for track data (the one which succeeded) where my code failed to respond to one of the queries in the group of metadata queries. The conversation looked like this:

Code:
AVRCP 0 GET_ELEMENT_ATTRIBUTES 02 05 04?

AVRCP 0 GET_ELEMENT_ATTRIBUTES 01 01?
AVRCP RSP 1 1 "Sultans of Swing"
AVRCP 0 GET_ELEMENT_ATTRIBUTES 01 03?
AVRCP RSP 1 3 "(Album N/A)"
AVRCP 0 GET_ELEMENT_ATTRIBUTES 01 02?
AVRCP RSP 1 2 "Dire Straits"


The first of those queries is doing a multi-query, it's asking for two items at once:
02 = Number of attributes being queried for
05 = Attribute code for the total number of tracks in the album.
04 = Attribute code for the current track number.

My code doesn't yet know how to respond to a multi-query. It only knows how to respond to single queries where the first number in the query is "01". The Honda stereo only ever sent single queries, never a multi-query.

I think what happened (this is just a hunch that I haven't tested yet) is that since I didn't respond to that first query in a timely fashion, its parent routine for making track metadata queries is hung waiting for a response and it won't ask again. It managed to get that one group of queries but now it won't do it again.

So I guess I have to write the full parser for the "GET_ELEMENT_ATTRIBUTES" responses that I was putting off writing.
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Tony Fabris

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#369741 - 06/11/2017 00:55 Re: BlueGigaEmpeg [Re: tfabris]
mlord
carpal tunnel

Registered: 29/08/2000
Posts: 13628
Loc: Canada
Agreed. Looks like the right thing to tackle!

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#369742 - 06/11/2017 09:10 Re: BlueGigaEmpeg [Re: mlord]
tfabris
carpal tunnel

Registered: 20/12/1999
Posts: 30784
Loc: Seattle, WA
Earlier you mentioned the tuner connector as a possible power source.

What voltage level is supplied on that connector and via which pins? Do you remember?
_________________________
Tony Fabris

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#369743 - 06/11/2017 12:04 Re: BlueGigaEmpeg [Re: tfabris]
mlord
carpal tunnel

Registered: 29/08/2000
Posts: 13628
Loc: Canada
My notes on the tuner connector show this:
Code:
the 8 way Molex 'tuner' connector is wired as follows:

1 - Pink - level
2 - Grey - signal
3 - Blue - Power Ant (not connected on wiring harness)
4 - Black - 0v (ground)
5 - Brown - TX (from tuner)
6 - Red - RX
7 - Purple - no connection (not used in PCATS tuner nor in factory tuner)
8 - Blue - 12v



Edited by mlord (06/11/2017 23:13)

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#369748 - 06/11/2017 19:19 Re: BlueGigaEmpeg [Re: mlord]
tfabris
carpal tunnel

Registered: 20/12/1999
Posts: 30784
Loc: Seattle, WA
Sweet! Thanks so much!
_________________________
Tony Fabris

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#369750 - 06/11/2017 22:36 Re: BlueGigaEmpeg [Re: mlord]
tfabris
carpal tunnel

Registered: 20/12/1999
Posts: 30784
Loc: Seattle, WA
Supplying power to the external circuit from the tuner plug connection (through a 5v power supply of course) works fine. The amount of noise is unchanged, but I much prefer the idea of my assembly connecting to this existing connector instead of trying to manage additional power connectors, so I'm going to roll forward with that. Thanks!
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Tony Fabris

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#369751 - 06/11/2017 23:09 Re: BlueGigaEmpeg [Re: tfabris]
mlord
carpal tunnel

Registered: 29/08/2000
Posts: 13628
Loc: Canada
Okay, I might pursue using the Tuner serial port for the BT module connection then. This way would leave the empeg's primary serial port available for the usual troubleshooting etc. without any conflicts or special handling needed.

The Tuner port is (I believe) 5V TTL logic, which will need to be voltage adapted for the 3.3V CMOS on the BT module. I expect just a couple of resistors will do the trick, but will find out when I do it here.

Cheers

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#369752 - 06/11/2017 23:11 Re: BlueGigaEmpeg [Re: tfabris]
mlord
carpal tunnel

Registered: 29/08/2000
Posts: 13628
Loc: Canada
So.. this noise. Is it drive related at all, or just present even with the drive "spun down" (can tell this by looking at the empeg display)?

Oh, and is the noise still there if you switch from the Pololu 5v adapter to your earlier 7805 regulator (with two capacitors)?



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#369753 - 07/11/2017 02:26 Re: BlueGigaEmpeg [Re: mlord]
tfabris
carpal tunnel

Registered: 20/12/1999
Posts: 30784
Loc: Seattle, WA
The noise is pretty faint so it's hard to be sure. It's at the level where you can't hear it unless the song has a really long faint fade-out.

The BlueGiga's ADC seems to have a "floor" or a "noise gate" where extremely quiet sounds don't get sent to the ADC at all and there's just digital silence. So for example, songs with long fade-ins or long fade-outs might have a very small bit of the quietest part of the fade cut off. The amount of noise I'm hearing is just barely on the edge of that noise gate's sensitivity level, so what I get is an intermittent thing where occasionally I hear a faint bit of noise floor appear for a second or so, then it drops below the sensitivity threshold of the noise gate then it fades out again. It's only audible if I turn up the volume on the head unit really loud. But my goal is to eliminate it completely so that even that's not a problem.

Side note: I've also looked through the commandset looing for a way to bring that noise gate's threshold setting down even further, so that it doesn't cut off even the quietest fadeouts. But I can't find any command to adjust the threshold of that noise gate. I'm already controlling the gain and the preamps and the mic bias voltage, and those are set correctly in my code, I can't find any other settings related to that.

I'm using an SSD so I can't tell if it's spinup/spindown related.

I haven't tried switching back to the 7805, I'm going to try switching forward to that isolated voltage converter instead, it comes in the mail tomorrow. If that doesn't solve the issue, I'll try comparing the three power supply types.
_________________________
Tony Fabris

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#369754 - 07/11/2017 05:54 Re: BlueGigaEmpeg [Re: tfabris]
tfabris
carpal tunnel

Registered: 20/12/1999
Posts: 30784
Loc: Seattle, WA
Another update to the source code here:
https://create.arduino.cc/editor/tfabris/4c5eea9a-1462-45d7-908d-81a5bb6b0d90/preview

This implements the proper responses to the head unit's queries for track metadata, in cases where it attempts to query for multiple pieces of metadata in the same query line.

I haven't gotten a chance to see if this fixes the problem with my roommate's Kenwood stereo yet. Crossing my fingers!
_________________________
Tony Fabris

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#369755 - 07/11/2017 08:29 Re: BlueGigaEmpeg [Re: tfabris]
tfabris
carpal tunnel

Registered: 20/12/1999
Posts: 30784
Loc: Seattle, WA
Hmph. The new code did not fix the problem.

It did allow the track number to be displayed on the Kenwood screen but again, only the first one. The Kenwood didnít query for subsequent ones.
_________________________
Tony Fabris

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#369756 - 07/11/2017 13:42 Re: BlueGigaEmpeg [Re: mlord]
tanstaafl.
carpal tunnel

Registered: 08/07/1999
Posts: 5313
Loc: Ajijic, Mexico
Originally Posted By: tfabris
The noise is pretty faint so it's hard to be sure. It's at the level where you can't hear it unless the song has a really long faint fade-out.
Rush, "Red Barchetta"?

Play the track on some other device to be sure the problem isn't in the track itself, and experiment with different tracks as well. I suspct you have already done those things, but that's the limit of my technical competence so is the only suggestion I can make.

tanstaafl.
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"There Ain't No Such Thing As A Free Lunch"

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#369757 - 07/11/2017 16:19 Re: BlueGigaEmpeg [Re: tanstaafl.]
tfabris
carpal tunnel

Registered: 20/12/1999
Posts: 30784
Loc: Seattle, WA
Thanks for that suggestion. Unfortunately itís not that simple. Iím using a large variety of tracks to test this, and I also have the ability to A/B with other playback systems and also with the pure digital versions via A2DP with my phone, so Iím certain I know the difference between noise floor extant in the track and noise added by external electronics.
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Tony Fabris

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#369758 - 08/11/2017 04:33 Re: BlueGigaEmpeg [Re: tfabris]
tfabris
carpal tunnel

Registered: 20/12/1999
Posts: 30784
Loc: Seattle, WA
OK weird.

I got the new isolated power supply and hooked it up and tried it out.

It seemed to work but it made a faint humming/whining noise during operation. Not noise in the audio chain, but I mean physical noise when I put me ear up next to it. I've heard power supplies that whine a bit before, so I thought maybe this was normal operation and kept trying it out.

The ground loop noise on the bluetooth/arduino/empeg assembly audio chain was even less than with previous power supplies. Not 100 percent gone, but definitely much much better. Prior versions of the noise were a combinaion of an electronic hum as well as a rushing-wind kind of static noise floor, but with the new power supply it was only the static noise floor, and that was pretty quiet.

Unfortunately I noticed that the bluetooth and arduino were a bit unstable, as if maybe it wasn't supplying the right voltage. Example of what I mean by "unstable" is that the bluetooth connection would drop occasionally, or the reset button that I implemented on the arduino would not function sometimes.

So I unplugged the new power supply and went back to the pololu power supply. And then I plugged in my USB debug cable into the Arudino to work on the programming side of things and... nothing. Nothing comes out on the debug cable.

What's interesting is that things go IN on the debug cable just fine. And the communication between the arduino and the bluetooth board are fine. I know this because of the behaviors I have programmed into my code. I can press the reset button and my blue LED connected to the arduino lights up and it erases the bluetooth pairing on the bluetooth chip, exactly as it is supposed to. I can do all the actions that I normally can do and they all work. I just don't see their output logs on my arduino serial debug monitor any more.

I can SEND commands to the bluetooth module by typing them into the arduino debug console and they get there, they arrive and do the correct thing. For instance if I type BOOT 0 into the arudino debug console then the bluetooth chip correctly reboots (it disconnects form whatever it was paired with and then reconnects after a moment). So SENDING text to the Arduino works.

But I don't see any serial ooutput coming BACK from the arudino. And I know that my program outputs stuff back (regardless of echo on or echo off), it's got specific logging commands that my program has said to put there, and those commands are in there pretty constantly from power-on. For instance, I can press my reset button and my blue LED lights up to indicate it's in paring mode, and I know at that moment I'm echoing a bunch of messages to the arduino debug serial port, but I'm not seeing them on the console.

I tried reloading a program onto the arduino, it times out because it can't get a serial signal back saying that it is receiving the code.

I tried fully unplugging the arduino from the entire assembly and connecting it solely to the computer just from the USB cable. Same thing.

I tried plugging it into an entirely different computer and different operating system (going from Mac to Windows), which entailed installing the arudino development software and device drivers from scratch on the new computer, same thing.

It's not a baud rate thing, because (a) the program sets the baud rate and I know the program is working, and (b) I tried different baud rates on the monitor anyway. Same thing.

Wow this is weird. I don't see how the new power supply could have done this to the arduino but I suppose it could? I don't know. Why would it fry only one direction of the arduino serial port while the rest of the thing works perfectly for everything else? Weird.

_________________________
Tony Fabris

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#369759 - 08/11/2017 04:40 Re: BlueGigaEmpeg [Re: tfabris]
tfabris
carpal tunnel

Registered: 20/12/1999
Posts: 30784
Loc: Seattle, WA
Thank goodness I had the foresight to buy a couple of arduino mega boards. Backup board works perfectly with no changes.
_________________________
Tony Fabris

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#369760 - 08/11/2017 07:06 Re: BlueGigaEmpeg [Re: tfabris]
tfabris
carpal tunnel

Registered: 20/12/1999
Posts: 30784
Loc: Seattle, WA
Another update to the source code.
https://create.arduino.cc/editor/tfabris/4c5eea9a-1462-45d7-908d-81a5bb6b0d90/preview

This makes it so that the same set of notification commands is always sent to the bluetooth chip every time a track changes or the playback status changes. This was an attempt to fix the bug with the Kenwood headunit where it only ever got the first track title on its screen and never got subsequent ones.

It didn't fix that bug, but it fixed another previously-unmentioned bug where I had a bluetooth headset which wasn't successfully pausing/unpausing when I pressed its pause button. Something about the change in the last set of code fixed that bug, and now the headset correctly pauses and unpauses.
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Tony Fabris

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#369761 - 08/11/2017 08:37 Re: BlueGigaEmpeg [Re: tfabris]
tfabris
carpal tunnel

Registered: 20/12/1999
Posts: 30784
Loc: Seattle, WA
Aha.

Updated example code that fixes the Kenwood bug:
https://create.arduino.cc/editor/tfabris/4c5eea9a-1462-45d7-908d-81a5bb6b0d90/preview

Here's what was going on with the Kenwood bug (from my code comments in the update above):

// Final fix for the "Kenwood Bug". Description of the Kenwood Bug:
// The AVRCP NFY CHANGED commands work on factory car stereo in
// Honda Accord 2017 model no matter what the transaction label is.
// This led me to believe that the transaction label was only important
// when performing an immediate response to a state query (i.e., when
// sending an "AVRCP NFY INTERIM" response), and that if I was the one
// who was indicating the state change (i.e., when I was sending an
// "AVRCP NFY CHANGED" statement to tell the host that something had
// changed), that the transaction label was arbitrary and that I was
// the person choosing the transaction label at that time. This was
// fine for the Honda stereo: When those commands are issued to the
// bluetooth chip, then the car stereo head unit immediately reacts
// by re-querying for more new track metadata from the bluetooth chip.
//
// However, when using those commands on a Kenwood bluetooth-equipped
// car stereo, then nothing happens when the messages are sent up
// with arbitrary transaction labels. The Kenwood stops sending new
// queries for track information and just "sits there" blindly
// playing the audio stream without getting any new track data.
//
// It turns out that the transaction labels aren't arbitrary if
// you received a "REGISTER_NOTIFICATION" message for the
// "PLAYBACK_STATUS_CHANGED" or the "TRACK_CHANGED" messages.
// Yes, you need to immediately respond with an "INTERIM"
// notification, but then if you send a "CHANGED" notification
// yourself later, then the transaction label still has to match.
// The Kenwood stopped querying for new track data because the
// transaction labels didn't match when I sent it "CHANGED"
// notifications. The fix is to match the transaction labels
// by storing them in a global variable.

As far as the noise goes, I think I'm going to attempt to make a first pass at a PCB and see if all I really need to eliminate the noise is to simply get things more solid with better ground traces and everything, instead of jerry rigged on a breadboard.
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Tony Fabris

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#369764 - 10/11/2017 04:29 Re: BlueGigaEmpeg [Re: tfabris]
tfabris
carpal tunnel

Registered: 20/12/1999
Posts: 30784
Loc: Seattle, WA
Now that the software and my breadboard prototype are working well, I've just ordered a PCB from Pad2Pad. Should have a video of the assembled version of that in the next 10 days or so. smile
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Tony Fabris

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#369768 - 11/11/2017 21:06 Re: BlueGigaEmpeg [Re: tfabris]
tfabris
carpal tunnel

Registered: 20/12/1999
Posts: 30784
Loc: Seattle, WA
I have done another update of the code. Some code cleanup and comment cleanup. Removed a few dead things in the code.
https://create.arduino.cc/editor/tfabris/4c5eea9a-1462-45d7-908d-81a5bb6b0d90/preview
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Tony Fabris

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