Mauricio Culibrk wrote:
Hi there!
I'm really sorry for bothering you.... I noticed your posts and patch on
the linux-mips mailing list....
and I'm very interested in ndelay patch you proposed.
I'm currently using some embedded mips-based boards for bit-banging SPI
and I2C implementations... but the current code uses udelay which is way
too "long" for the purporse...
I'm wondering if you have any updated/fixed patch available as you
mention that on the list (that you'll fix your patch a little regarding
all the comments received)
Anyway... I'm using some "consumer" boards based on Atheros WiSoCs
AR2315, AR2317... and Broadcom chips which should have MIPS32 MIPS4K
cores...
this cpu should have a "functioning cr0 register", right? (as I have
absolutely no "datasheets" available to check for that)
The latest version of the ndelay patch is version 3, which disables
interrupts to ensure the Count register doesn't wrap. If you have
interrupts disabled already, there is another function you can can call.
You can get the version 3 patch from the mailing list archive at
http://www.linux-mips.org/archives/linux-mips/2009-03/msg00073.html
I haven't received much feedback since the first version of the patch,
and it's something we're already using, so I think it's in pretty good
shape. And, as I understand it, R4000-series processors should be in
shape as far as a good Count register. Part of the version 3 patch adds
dependencies so that it will only appear in your favorite configuration
tool if you've selected a processor on which it will work. Ralf has
mentioned some issues with some R4000 processors, though.
As the code stands on my 24K processor, a requested delay of 100 nsec
ends up as an actual delay of a bit over 130 nsec. Not perfect, but
definitely less than 1000 nsec. I have been thinking about adding in a
calibration constant that should get it closer, but it hasn't been
important yet and I wanted the basic patch to get accepted before I did
anything *really* obscure.
