using the tuner port as a ttl serial port

Ok now that I've got my GPS up and running on my serial port of the empeg, I'm both happy and sad.. happy because GPSApp is soo cool but sad because I will never be able to try out some ODB-II connectivity I was planning too.
So I noticed this post by Hugo, which basically says that the tuner module is TTL RS232. So it would actually be quite simple to hook up most GPS modules to the tuner serial port, since GPS modules like the Oncore and others use TTL RS232. This would then free up the standard serial port for other applications like ODB-II.
The only problem with this would be software-wise, the player app locks the tuner serial port I'm sure. So my question: Is it possible to "rename" the tuner serial port so the player app can't find it. I.e. instead of making it /dev/ttsyX could we make it come up as /dev/ttsyZ?
Yes duh I would never be able to use a tuner module but I'm not much of a solderer so I don't anticiapte buying a kit when they become available....
Any ideas how to make the tuner port invisible to the player?

Why not ask the gps app guys to allow config'ing the used comm port via the config.ini file??

Just a thought...

-Ben-O-Rama

That would be easy enough but the problem still is the player app will be locking the ttl serial port. I need to know how to "fake" the player app so it can't find this port

gpsapp can be started before the player.

The player didn't lock the serial port even though it was using it, so it is probably similar with the tuner port. But even without locking problems the player might interfere by reading data before gpsapp can get it's hands on it.

So I gather no one knows of any way to "move" the tuner serial port to another /dev/ttSy entry? Seems like there should be a trick to doing this..oh well there's always the kernel source I guess.

mv should work. it binds the hardware based on the major/minor device numbers, not the names.

Cool I did not know this about linux. I will try this sometime and see what happens. Now the problem is figuring out if the inverted TTL of the tuner port is compatible with the Oncore receiver. If it is it will be the easiest circuit ever for installing this GPS on the empeg.

TTL is TTL. The Oncore is TTL. It all really depends on what is meant by inverted TTL wrt to RS232..

If by inverted TTL you mean that 'Serial 0' <=> 5V, and 'Serial 1' <=> 0V, ie it's inverted 'serial' logic at TTL levels, then you'll probably need a couple of inverters. (Hint - Often a Quad Nand gate is easier/cheaper to obtain than a dual/quad Not gate...)

If by inverted TTL you mean that 'Serial 0' <=> 0V, and 'Serial 1' <=> 5V, ie it's inverted 'RS232' logic at TTL levels, then it should be plug'n'play.

One thing to beware of though, is that since the tuner port is TTL level, it's circuitry protection will far less hardy than the real serial port (serial transceiver chips are almost bombproof). 'Real' TTL can be damaged by >6.5V. I'm not certain, but ISTR that all of the empegs serial ports are onboard the Arm CPU, ie no separate serial UART. If this is the case, then blowing the tuner's serial port might be synonymous with blowing up your CPU, ie expensive.

You might want to get the Empeg guys to weigh in on this.

couldn't agree more with genixia's comments/warning, and also note that there are [from Hugos comments] - no current limiting resistors on these TTL lines (the current limiting resistors are provided by the tuner module when its plugged in) so if you don't put some in, you may your self with a dead empeg quicker than you think.

I would *STRONGLY* suggest that if you want to go down this path and use it for your TTL level GPS that you consider putting 2 Serial Transceiver chips inline (and back to back) with your GPS unit anyway - you will find this gives you plenty of protection if done right.

Be aware also that there is only +12 volts voltage available on the Tuner module interface - so you'll need a good 12V->5volts voltage regulator as well to drive your GPS and make sure tha the GPS has a common ground connection with respect to the empeg or you may find yourself killing your empeg through ground loops and voltage spikes...

Anyway, go the safe route and use the real serial port for now. There's at least 2 projects in early stages that could lead to multiple serial ports being available. Chimera is looking at a USB based extender that will hopefully allow USB<->serial dongles to be used with the empeg, and I'm about 75% done on a pcb design to muliplex the serial port into something more useful (including OBDII and Oncore support). I got stalled over Christmas, but hope to get cracking again soon.

If anyone out there is a PIC expert and wants to help, please weigh in..

Sounds logical.. I'll wait then although I still think a ttl serial port option would be useful just because a lot of things we might want to us will be ttl levels, just a thought.

Ok, I'll look into making (protected) TTL levels accessible in my design.