Re: Serial connection is garbled at 32MHz

Hi Greg,

On Fri, 04 Apr 2008 11:06:59 +1000
Greg Ungerer <[email protected]> wrote:

> 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).


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.

Thanks.

Alex



-- 
 -- 
---------------------------------------------
Loren A. Linden Levy
Department of Physics 
390 UCB 
University of Colorado
Boulder, CO   80309-0390
Tel:   303-735-6146 (CU) / +049 040 8998 4789 (DESY) 
Fax:   303-492-3352 (CU) / +049 040 8998 4034 (DESY) 
Cell:  303-332-2768 (U.S.) / +049 (0)151 5496 1831 (Germany)
Email: [email protected]
url:   http://up.colorado.edu/~lindenle
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