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 */
