On Jun 7, 2013, at 12:19 AM, Chris Albertson <[email protected]> wrote:
> If you look at PHK's code in FreeBSD this is what is done. The PPS signal >> gates the timer, so no interrupt is involved in the time stamp precision. >> But yes, it would be interesting to do something on a FPGA. Unfortunately I >> wouldn't be able to get to anything like that myself in this lifetime. > > Does the hardware on the NET4501 allow this? Standard PC hardware doesn't. > I thought the 4501 used a "Pentium" CPU and the counter would be internal > to the CPU and you'd have to read out the count in an interrupt handler. > I have read the Linux code for this, which I hear is about the same as BSD. > But then I read the common x86 achitecture. The Net4501 isn't standard PC hardware. It uses the AMD Elan SC520 processor, which is essentially a 133 MHz i486, with some additional goodies, such as internal counters. A little bit of soldering is required to get the right electrical connections to make it happen, but John Ackerman describes it pretty well here: http://www.febo.com/pages/soekris/ The FreeBSD code to read the timer is here http://svnweb.freebsd.org/base/head/sys/i386/i386/elan-mmcr.c?view=markup&pathrev=214346 Look starting at line 224. Ralph _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
