Make an expansion board with a serial port(s) for WL-500b/g

[wtzm]

As far as I understand you, your comp always receive bytes from WL without errors ('cause PMON only send data, don't receive it), but WL sometimes "misunderstand" bytes from comp (when you try to work with shell) ?

Not completely correct. I have communicated with PMON (if you cancel the boot with Ctrl+C) succesfully und this works - I can issue commands, etc.
With PMON if I send an 'o' it receives (and echoes back) an 'o'. This doesn't work on the console (after bootup). Sometimes it echoes a few 'o', or it acts as if I had transmitted a line-feed.
In the meantime I have conducted tests with my 12,75MHz Crytal. The results are the same...
By the way from where do you know that PMON expects a frequency of 7x the standard (1.8432MHz)?
I still have the opinion that 13,5MHz is the value that the linux kernel expects for serial port initialization (-> sbmips.c).

[Artie]

Not completely correct. I have communicated with PMON (if you cancel the boot with Ctrl+C) succesfully und this works - I can issue commands, etc.
With PMON if I send an 'o' it receives (and echoes back) an 'o'. This doesn't work on the console (after bootup). Sometimes it echoes a few 'o', or it acts as if I had transmitted a line-feed.
In the meantime I have conducted tests with my 12,75MHz Crytal. The results are the same...

Sorry, then I have no ideas.

You can try to send some characters with chess-board patterns in upper nibble (for example 0x55 - 'U' or 0xAA - 'ê') and check how they will be echoed back...

By the way from where do you know that PMON expects a frequency of 7x the standard (1.8432MHz)?
I still have the opinion that 13,5MHz is the value that the linux kernel expects for serial port initialization (-> sbmips.c).

Frequency from XTAL1 pin in all UART chips (if they are 8250 compatible, of course) divided by 16-bit value of DLL/DLH register pair (and you can see this frequency at BAUDOUT' pin of your UART by scope) then divided by 16; - thus we get needed baudrate.
So, to get 115200 baud with 13.5MHz crystal we must load DLL/DLH with value of 7,32421875... But this registers are integer , so we can only load either 7 or 8. - In first case we will have 120536 baud, in second - 105469. Not 115200...

Btw, my port-extender to WL500G works fine with "canonical" 1.843MHz (look at generator on second photo) - it's only needed to set PC terminal to 16457 baud. Some terminal programs doesn't know how to do this, but mine - know.
Another way to get 115200 baud with 1.843 quartz - setserial /dev/tts/0 baud_base 115200 divisor 1 spd_cust (but this will work only untill reboot, of course).