Re: Serial connection is garbled at 32MHz

Hi Loren,

Loren A. Linden Levy wrote:
> On Fri, 04 Apr 2008 11:06:59 +1000
> Greg Ungerer <[email protected]> wrote:
>> 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).
> 
> 
> It is a 2.4.x kernel and I actually already added the 32MHz option
> (coldfire.h):
> 
> --- linux-2.4.x/include/asm-m68knommu/coldfire.h        25 Sep 2007 06:25:01 -0000      1.19
> +++ linux-2.4.x/include/asm-m68knommu/coldfire.h        4 Apr 2008 17:46:52 -0000
> @@ -38,6 +38,7 @@
>  /*
>   *     Define master clock frequency.
>   */
> +
>  #if defined(CONFIG_CLOCK_11MHz)
>  #define        MCF_CLK         11289600
>  #elif defined(CONFIG_CLOCK_16MHz)
> @@ -50,6 +51,8 @@
>  #define        MCF_CLK         25000000
>  #elif defined(CONFIG_CLOCK_29_5MHz)
>  #define        MCF_CLK         29500000
> +#elif defined(CONFIG_CLOCK_32MHz)
> +#define        MCF_CLK         32000000
>  #elif defined(CONFIG_CLOCK_33MHz)
>  #define        MCF_CLK         33000000
>  #elif defined(CONFIG_CLOCK_40MHz)
> 
> 
> and an entry in the config.in file for kernel configuration.
> 
> --- linux-2.4.x/arch/m68knommu/config.in        25 Sep 2007 06:25:01 -0000     1.76
> +++ linux-2.4.x/arch/m68knommu/config.in        4 Apr 2008 17:46:09 -0000
> @@ -34,7 +34,6 @@
>  endmenu
>  
>  #############################################################################
> -
>  mainmenu_option next_comment
>  comment 'Processor type and features'
>  
> @@ -93,6 +92,7 @@
>          24MHz  CONFIG_CLOCK_24MHz \
>          25MHz  CONFIG_CLOCK_25MHz \
>          29.5MHz CONFIG_CLOCK_29_5MHz \
> +        32MHz  CONFIG_CLOCK_32MHz \
>          33MHz  CONFIG_CLOCK_33MHz \
>          40MHz  CONFIG_CLOCK_40MHz \
>          45MHz  CONFIG_CLOCK_45MHz \
> 
>  
> Now I am a little confused about the serial baudrate calculation (I
> found it is actually in the file drivers/char/mcfserial.c).
> 
> For the M5282 the calculation is:
> 
> #else
>         baudclk = ((MCF_BUSCLK / mcfrs_baud_table[i]) + 16) / 32;
> #endif
> 
> Which is basically identical to what I found in the manual.  Here the
> baud_rate table entry is number 14 which is 19200. So the baudclck for
> 32MHz and 66MHz come out to be 52 and 180 respectively. I guess i do not understand why I am getting junk out if the clock calculation here is being mad correctly. I am in the process of looking throiugh the UART UBG settings to se iff there is something I am missing. Any input or hints would be appreciated.

Seems like you have taken the correct approach.

Regards
Greg



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