Re: Serial connection is garbled at 32MHz

Hi Allon, Loren,

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

That is right. If you are just feeding a different master
clock to the 5282 then the right change to make is to
CONFIG_CLOCK_FREQ. Look for the config menu item with the
text "Set the core clock frequency". This is only in 2.6.x
kernels.

If using a 2.4.x kernel then you need to change the clock
frequency manually in the source (look in 
linux-2.4.x/include/asm-arm/coldfire.h).

Regards
Greg


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Greg Ungerer  --  Chief Software Dude       EMAIL:     [email protected]
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