Roland Tollenaar wrote:
HI Wolfgang,
It was the IXXAT PCI card currently plugged into my test PC but I
actually recommand the PEAK PCI card. It's also much cheaper, I guess.
Tomorrow I'm going to repeat the tests with this card ... stay tuned.
Clear. Thanks for the advice.
Here is a revised list of the register access times:
PEAK-Dongle: register read : 11705ns ( 85428/sec)
PEAK-Dongle: register write: 11687ns ( 85562/sec)
IXXAT-PCI : register read : 725ns (1378643/sec)
IXXAT-PCI : register write: 301ns (3311667/sec)
PEAK-PCI : register read : 486ns (2057468/sec)
PEAK-PCI : register write: 161ns (6201956/sec)
I will continue development on my laptop with the dongle for the time
being. It would be interesting to see what happens to the latency
after your proposed changes are in effect.
Non-CAN latencies will not be significantly affected but RT-Socket-CAN
latencies will be worse due to overhead of interrupt handling by the
service task.
BTW, what are the latencies you measure on your system under load
(without RT-Socket-CAN).
Off the top of my head 25us average 30us to 35us max. I am not sure I am
"loading" the system though. How do I measure this load that is always
talked about?
Roland
Wolfgang.
Thanks,
Roland
Wolfgang Grandegger wrote:
Hallo,
in the meantime I have measured the latencies introduced through
messages sent and received by RT-Socket-CAN. The SJA1000 register
access times on my rather old PC with an Athlon 1100 Mhz are:
PEAK-Dongle: read access: 11807 ns
PEAK-Dongle: write access: 11677 ns
IXXAT-PCI : read access: 729 ns
IXXAT-PCI : write access: 305 ns
I measured an increase of the latency of approx. 170us with the
PEAK-Dongle and approx 13us with the IXXAT-PCI card for the
reception of a full CAN message (with 8 bytes payload). Sending
messages is a bit less disturbing. I have attached a small patch to
measure the SJA1000 register access times when the driver is
initialized. You are welcome to apply it on your setup and report
the results. I'm especially interested in numbers for the ISA bus
(or PC-104).
Wolfgang.
------------------------------------------------------------------------
+ diff -u xenomai/ksrc/drivers/can/rtcan_dev.c.IOTEST
xenomai/ksrc/drivers/can/rtcan_dev.c
+ diff -u xenomai/ksrc/drivers/can/sja1000/rtcan_sja1000.c.IOTEST
xenomai/ksrc/drivers/can/sja1000/rtcan_sja1000.c
--- xenomai/ksrc/drivers/can/sja1000/rtcan_sja1000.c.IOTEST
2007-02-26 09:17:27.000000000 +0100
+++ xenomai/ksrc/drivers/can/sja1000/rtcan_sja1000.c 2007-03-13
10:01:47.000000000 +0100
@@ -728,6 +728,30 @@
if (chip == NULL)
return -EINVAL;
+#if 1
+ {
+ nanosecs_abs_t begin, diff;
+ volatile u8 reg;
+ int i, count = 100000;
+ begin = rtdm_clock_read();
+ for (i = 0; i < count; i++) {
+ reg = chip->read_reg(dev, 0);
+ }
+ diff = rtdm_clock_read() - begin;
+ printk("%s: register read time for %d accessed: %ld (%ld per
access)\n",
+ dev->board_name, count,
+ (unsigned long)diff, (unsigned long)diff / count);
+ begin = rtdm_clock_read();
+ for (i = 0; i < count; i++) {
+ chip->write_reg(dev, 0, reg);
+ }
+ diff = rtdm_clock_read() - begin;
+ printk("%s: register write time for %d accessed: %ld (%ld per
access)\n",
+ dev->board_name, count,
+ (unsigned long)diff, (unsigned long)diff / count);
+ }
+#endif
+
/* Set dummy state for following call */
dev->state = CAN_STATE_ACTIVE;
/* Enter reset mode */
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