Re: Serial connection is garbled at 32MHz

On Apr 3, 2008, at 2:20 PM, Loren A. Linden Levy wrote:

> Hi Guys,
>
> So I am making progress with this external FPGA (thanks to all the
> help) and I have the code basically working (I think). One thing we
> are doing is artificially running the chip (M%282) at 32MHz and this
> screws up the display over serial (I get nonsense characters). This is
> not too big a deal b/c I can connect just fine over telnet I was just
> wondering if there was an obvious way to fix it (settings?). Thanks
> again.

I'd suggest looking at (assuming 2.6) linux2.6.x/drivers/serial/ 
mcfserial.c

Look for the line (#636 in my kernel):
/* compute the baudrate clock */

This is where it determines the baudrate clock based on the CPU clock.

It appears to be based off of MCF_BUSCLK, which is defined in
linux2.6.x./include/asm-m68knommu/coldfire.h as
#define      MCF_BUSCLK      (CONFIG_CLOCK_FREQ / CONFIG_CLOCK_DIV)

Both CONFIG_CLOCK_FREQ  and CONFIG_CLOCK_DIV are defined in  
your .config.

If you're changing the clock on the fly, then you need to figure out  
what to change in the UART registers.

Enjoy!
-
allon
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