Weird problem on rs232 vs USB-serial...

Chris Johns chrisj at
Tue Feb 24 00:17:58 UTC 2009

mike wrote:
> Joel Sherrill wrote:
>>> One more addition is:
>>> - if I use 'grmon' to connect to the DSU port, then load the same app 
>>> with grmon and run,
>>> I can see outputs coming out of the COM1 port.
>>> - it was when I used the onboard bootrom to load the app to ram, then 
>>> jump to it that I didn't
>>> see any outputs on COM1 port. Again, when it's connected to 
>>> USB<->serial, the outputs
>>> came out fine, with the same app.
>> Could the flow control settings be wrong in the comm application when 
>> using the ttys0?
>> I recall that minicom on unix defaults to HW flow control on.
> Thanks Joel, I did set the minicom to use 'no flow control'...
> It seems that the only variable is "ttyS1" vs "ttyUSB0" but I don't know 
> what else to look...

Check /proc/interrupts to see if the kernel is getting interrupts from the 
UART for ttyS1. I would not bother with USB interrupts as this is a shared bus 
and the interrupt count to USB serial I/O does not match easily.

I would also connect just a cable to the port and connect together the TX/RX 
pins then type something on Minicom. You should see the interrupt count go up 
by 2 for each character pressed. This will help you isolate the host from 
cable from target.


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