Re: [Xenomai-core] Re: RT-Socket-CAN bus error rate and latencies
Jan Kiszka wrote: Wolfgang Grandegger wrote: OK, I have just commited the following changes: 2007-04-02 Wolfgang Grandegger <[EMAIL PROTECTED]> * ksrc/drivers/can/*: The option CONFIG_XENO_DRIVERS_CAN_BUS_ERR now enables bus error interrupts when an application is calling a receive function on a socket listening on bus errors. After one bus error has occured, the interrupt will be disabled to allow the application time for error processing and to efficiently avoid bus error interrupt flooding. This option is automatically selected for CAN controllers supporting bus error interrupts like the SJA1000. Just one final nitpicking question: Who's to read the help text of CONFIG_XENO_DRIVERS_CAN_BUS_ERR - except people reading Kconfig directly? (My point is that this explanation may rather become a code comment.) Good hint. Patch comes soon. At least it's already documented in the API doc. Wolfgang. ___ Xenomai-core mailing list Xenomai-core@gna.org https://mail.gna.org/listinfo/xenomai-core
Re: [Xenomai-core] Re: RT-Socket-CAN bus error rate and latencies
Wolfgang Grandegger wrote: > OK, I have just commited the following changes: > > 2007-04-02 Wolfgang Grandegger <[EMAIL PROTECTED]> > > * ksrc/drivers/can/*: The option CONFIG_XENO_DRIVERS_CAN_BUS_ERR now > enables bus error interrupts when an application is calling a receive > function on a socket listening on bus errors. After one bus error has > occured, the interrupt will be disabled to allow the application time > for error processing and to efficiently avoid bus error interrupt > flooding. This option is automatically selected for CAN controllers > supporting bus error interrupts like the SJA1000. Just one final nitpicking question: Who's to read the help text of CONFIG_XENO_DRIVERS_CAN_BUS_ERR - except people reading Kconfig directly? (My point is that this explanation may rather become a code comment.) Jan signature.asc Description: OpenPGP digital signature ___ Xenomai-core mailing list Xenomai-core@gna.org https://mail.gna.org/listinfo/xenomai-core
Re: [Xenomai-core] Re: RT-Socket-CAN bus error rate and latencies
Hello,
Jan Kiszka wrote:
Wolfgang Grandegger wrote:
...
Attached is the patch and it works fine. The key function
rtcan_sja_enable_bus_err() is called from sendmsg():
void rtcan_sja_enable_bus_err(struct rtcan_device *dev)
{
struct rtcan_sja1000 *chip = (struct rtcan_sja1000 *)dev->priv;
if (chip->bus_err_on < 2) {
if (chip->bus_err_on < 1)
chip->read_reg(dev, SJA_ECC);
chip->bus_err_on = 2;
}
}
And I do also do not see a real problem with multiple readers. I would
commit this solution. I'm just unsure if we should select it silently or
if the user should have the choice.
I would say no to user-selectability unless someone comes up with a
serious downside of this approach.
Are there any other error interrupt sources we should treat the same
way? Or all? Just to make the behaviour as regular as reasonable. I have
no opinion yet, I only want to make sure we have considered this as well
before we set the change API in stone.
Nice work!
OK, I have just commited the following changes:
2007-04-02 Wolfgang Grandegger <[EMAIL PROTECTED]>
* ksrc/drivers/can/*: The option CONFIG_XENO_DRIVERS_CAN_BUS_ERR now
enables bus error interrupts when an application is calling a receive
function on a socket listening on bus errors. After one bus error has
occured, the interrupt will be disabled to allow the application time
for error processing and to efficiently avoid bus error interrupt
flooding. This option is automatically selected for CAN controllers
supporting bus error interrupts like the SJA1000.
* include/rtdm/rtcan.h: Add some doc on bus-off and bus-error error
conditions and the restart policy.
* src/utils/can/rtcanconfig.c: Controller mode settings and doc
has been corrected.
Wolfgang.
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Re: [Xenomai-core] Re: RT-Socket-CAN bus error rate and latencies
Wolfgang Grandegger wrote:
> ...
> Attached is the patch and it works fine. The key function
> rtcan_sja_enable_bus_err() is called from sendmsg():
>
> void rtcan_sja_enable_bus_err(struct rtcan_device *dev)
> {
> struct rtcan_sja1000 *chip = (struct rtcan_sja1000 *)dev->priv;
>
> if (chip->bus_err_on < 2) {
> if (chip->bus_err_on < 1)
> chip->read_reg(dev, SJA_ECC);
> chip->bus_err_on = 2;
> }
> }
>
> And I do also do not see a real problem with multiple readers. I would
> commit this solution. I'm just unsure if we should select it silently or
> if the user should have the choice.
I would say no to user-selectability unless someone comes up with a
serious downside of this approach.
Are there any other error interrupt sources we should treat the same
way? Or all? Just to make the behaviour as regular as reasonable. I have
no opinion yet, I only want to make sure we have considered this as well
before we set the change API in stone.
Nice work!
Jan
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Re: [Xenomai-core] Re: RT-Socket-CAN bus error rate and latencies
Wolfgang Grandegger wrote:
Jan Kiszka wrote:
Oliver Hartkopp wrote:
Additionally to the written stuff below (please read that first), i want
to remark:
- Remember that we are talking about a case that is not a standard
operation mode but a (temporary) error condition that normally leads to
a bus-off state and appears only in development and hardware setup
phase!
- i would suggest to use some low resolution timestamp (like jiffies)
for this, which is very cheap in CPU usage
- the throttling should be configured as a driver module parameter (e.g.
bei_thr=0 or bei_thr=200 )due to the need of the global use-case. If you
are writing a CAN analysis tool you might want to set bei_thr=0 in other
cases a default of 200ms might be the right thing.
We are falling back to #1, i.e. where we are now already. Your
suggestion doesn't help us to provide a generic RT-stack for Xenomai.
Regards,
Oliver
Oliver Hartkopp wrote:
Wolfgang Grandegger wrote:
Jan Kiszka wrote:
Wolfgang Grandegger wrote:
Oliver Hartkopp wrote:
I would tend to reduce the notifications to the user by creating a
timer at the first bus error interrupt. The first BE irq would
lead to a CAN_ERR_BUSERROR and after a (configurable) time
(e.g.250ms) the next information about bus errors is allowed to be
passed to the user. After this time period is over a new
CAN_ERR_BUSERROR may be passed to the user containing the count of
occurred bus errors somewhere in the data[]-section of the Error
Frame. When a normal RX/TX-interrupt indicates a 'working' CAN
again, the timer would be terminated.
Instead of a fix configurable time we could also think about a
dynamic behaviour (e.g. with increasing periods).
What do you think about this?
The question is if one bus-error does provide enough information on
the cause of the electrical problem or if a sequence is better.
Furthermore, I personally regard the use of timers as to heavy. But
the solution is feasible, of course. Any other opinions?
I think Oliver's suggestions points in the right direction. But
instead
of only coding a timer into the stack, I still vote for closing the
loop
over the application:
After the first error in a potential series, the related error
frame is
queued, listeners are woken up, and BEI is disabled for now. Once
some
listener read the error frame *and* decided to call into the stack
for
further bus errors, BEI is enabled again.
That way the application decides about the error-related IRQ rate and
can easily throttle it by delaying the next receive call. Moreover,
threads of higher priority will be delayed at worst by one error IRQ.
This mechanism just needs some words in the documentation ("Be
warned:
error frames may overwhelm you. Throttle your reception!"), but no
further user-visible config options.
I understand, BEI interrupts get (re-)enabled in recvmsg() if the
socket wants to receive bus errors. There can me multiple readers,
but that's not a problem. Just some overhead in this function. This
would also simplify the implementation as my previous one with
"on-demand" bus error would be obsolete. I start to like this
solution.
Hm - to reenable the BEI on user interaction would be a nice thing
BUT i
can see several problems:
1. In socketcan you have receive queues into the userspace with a
length >1
Can you explain to me what the problem behind this is? I don't see it
yet.
2. How can we handle multiple subscribers (A reads three error frames
and reenables therefore the BEI, B reads nothing in this time). Please
remember: To have multiple applications it a vital idea from socketcan.
Same here, I don't see the issue. A and B will both find the first error
frame in their queues/ring buffers/whatever. If A has higher priority
(or gets an earlier timeslice), it may already re-enable BEI before B
was able to run as well. But that's an application-specific scheduling
issue and not a problem of the CAN stack (often it is precisely what you
want when assigning priorities...).
3. The count of occured BEIs gets lost (maybe this is unimportant)
Agreed, but I also don't consider this problematic.
Regarding (2) the solution could be not to reenable the BEI for a
device
until every subscriber has read his error frame. But this collides with
a raw-socket that's bound to 'any' device (ifindex = 0).
That can cause prio-inversion: a low-prio BEI-reader decides about when
a high-prio one gets the next message. No-go for RT.
Regarding (3) we could count the BEIs (which would not reduce the
interrupt load) or we just stop the BEI after the first occurance which
might possibly not enough for some people to implement the CAN
academical correct.
As you may see here a tight coupling of the problems on the CAN bus
with
the application(s!) is very tricky or even impossible in socketcan.
Regarding other network devices (like ethernet devices) the
notification
about Layer 1/2 problems is unusual. The concept of creating error
frames was a good comp
