Sebastian Smolorz wrote:
Wolfgang Grandegger wrote:
Access to the parallel port is slow, indeed. Looking to
rtcan_peak_dng_epp_readreg tells me, that 6 inb/outb are required to
read one register and if every inb/outb takes up 1-2 us ... puh ... the
problem gets obvious. Nevertheless, this problem is special for the PCAN
dongle and it seems to be a bad choice for RT-Socket-CAN. All other
devices can read/write registers much faster. I'm going to do some more
tests next week, also with other CAN hardware. Sebastian, have you
realized similar latency problems with SJA1000 on the ISA bus (which is
slow as well)?
No, I didn't realize any latency problems with the ISA CAN controller.
However, I didn't made any discrete latency measure tests. But the fact that
the SJA1000 driver is used on all robots of the RTS with 1 MB/s laser
scanners and a few more CAN nodes shows me that the latency impact is not
critical.
OK, I did'nt expected that reading approx. 15 bytes is really critical.
But the problem exists and reading these from the ISA bus likely also
takes 10..20 us.
Sebastian's opinion is that making it interruptible would be "the
start of chaos". I am sure he knows more about this than I ever will
but only out of academic interest before I sort this problem out
outside the realm of rtcan, I would like to know why.
As I see it, the right solution would be to handle the CAN interrupts by
a service task and disabled the corresponding IRQ till it's handled. I
do not see a real problem with this method,
I didn't say it's impossible. My point was that making the CAN ISR just
interruptible with no other changes is not enough.
but it requires substantial
implementation effort.
Right, and for users who don't have such hardware limits like Roland it is
probably more important that CAN interrupts are processed with no deferral.
So we would have to deal with both needs. Therefore my statement in a
previous mail that all the necessary work won't be done in five minutes.
Well, I know but it already got a rather high position on the wish list.
Wolfgang,
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