[Gta04-owner] Switching from RS232 to IrDA for debugging

[Dr. H. Nikolaus Schaller]

Hi Sven,

Am 20.07.2012 um 13:36 schrieb Sven Dyroff:

> Hello Nikolaus, 
> 
> I finally want to make my first steps in looking deeper into the GTA04 and therefor I need access to the serial port. After having taken a look into the schematics I still don't intend to open my GTA04 for this reason, because it seems that only one GPIO is to be toggled, so that we can connect _WIRELESS_ over IrDA to the UART of the OMAP. 
> 
> Is it possible that you build a new MLO that sets this GPIO to zero? So we only need to replace this new MLO with the current one on the SD card and then can debug over IrDA. Whenever we don't want

Yes, changing the GPIO is definitively possible. It should be done in this file:

http://git.goldelico.com/?p=gta04-xloader.git;a=blob;f=board/omap3530gta04/omap3530gta04.c;h=04f310d14e91276f207a524f9ea96b6d12715b9f;hb=HEAD

around line 1100. Maybe, changing the pull-up/down may be sufficient.

But to make it work, I think it is also needs to configure the UART a little differently since the IrDA protocol uses impulse patterns to indicate 0 and 1 states of the serialized data bytes. I.e. just adding a LED to a TX line and switching it on if a 0 is transmitted, doesn't make it IrDA receivable.

> anymore to widespread our internal data into our environment for everyone, but want to save some battery power, we just need to replace the MLO again...  ;-)) 
> 
> This idea only as a first step. The more better solution would be, that the bootloader switches this GPIO according to the existence of a flag-file like "IrDa.flag" within the FAT filesystem. And of course the best solution would be to have the possibility to set or remove this flag-file with a button, presented by the bootloader... 

Well, the MLO could also check the AUX button being pressed, since it is also a GPIO.

But I better like your idea of a special MLO variant, so that you can put it in a SD card you use for kernel work. So it is not necessary to add this feature to any MLO.

One other aspect to consider is that it is not possible to run the full IrDA protocol. Just the lowest level stuff.
I.e. there is no error correction so you may garble u-boot commands you send to the device...

So you need a special driver on your host-pc as well, that bypasses the IrDA protocol stack.

> Of couse I hope that currently the kernel doesn't set this GPIO. Am I right in this assumption? 

The current kernel doesn't touch the GPIO, but there should be a driver to enable IrDA from user space...

Nikolaus

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