Re: Serial connection is garbled at 32MHz

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Hi Loren,

Loren A. Linden Levy wrote:
> So do I need to maybe change something in my minicom setup?

I doubt it. Check with another serial device known to work
at that baud rate.

If you have access to a CRO then measure the character
length output on the serial line and you will at least
know what is actually being generated. Perhaps that clue
will help.

Regards
Greg



> On Mon, 07 Apr 2008 10:50:44 +1000
> Greg Ungerer <[email protected]> wrote:
> 
>> 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
>>
>>
>>
>> ------------------------------------------------------------------------
>> Greg Ungerer  --  Chief Software Dude       EMAIL:     [email protected]
>> Secure Computing Corporation                PHONE:       +61 7 3435 2888
>> 825 Stanley St,                             FAX:         +61 7 3891 3630
>> Woolloongabba, QLD, 4102, Australia         WEB: http://www.SnapGear.com
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> 
> 


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Greg Ungerer  --  Chief Software Dude       EMAIL:     [email protected]
SnapGear -- a Secure Computing Company      PHONE:       +61 7 3435 2888
825 Stanley St,                             FAX:         +61 7 3891 3630
Woolloongabba, QLD, 4102, Australia         WEB: http://www.SnapGear.com
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