[linux-dvb] Re: timing in dvb-kernel

[Oliver Endriss <o.endriss@gmx.de>]

On Monday 24 November 2003 15:28, Jeremy Hall wrote:
> Per some suggestions, I opted to try the dvb-kernel tree, but found that 
> timing is worse in the dvb-kernel.
> 
> I have requirements to be able to change voltage from h to v in under 8ms 
> consistently, and can successfully achieve this with the DVB code, but 
> dvb-kernel seems not able to do this.  Do you have suggestions on what I 
> might try to improve the latency?

This requires two modifications:
[1] I committed a change to 'dvb-kernel' which increases speed of the
    I2C bus for *full-featured* cards to 275 kHz (same value as in DVB).
    Please update file av7110.c from dvb-kernel CVS.

[2] Apply the following patch to saa7146_i2c.c:

-----------------  snip  ----------------------------
diff -p -u -r1.26 saa7146_i2c.c
--- saa7146_i2c.c	14 Nov 2003 11:42:04 -0000	1.26
+++ saa7146_i2c.c	25 Nov 2003 03:29:29 -0000
@@ -301,7 +301,7 @@ int saa7146_i2c_transfer(struct saa7146_
 		goto out;
 	}
 
-        if (count > 3) short_delay = 1;
+        short_delay = 1; // OE test
   
 	do {
 		/* reset the i2c-device if necessary */
-----------------  snip  ----------------------------

Note that without [2] modification [1] is almost useless,
because each I2C access causes a delay of 10..20ms.
I suggested several times to improve this but I was ignored...

Oliver


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