Re: [Xenomai-help] problem with rt_task_send() timeout and timer overruns

[Philippe Gerum <rpm@xenomai.org>]

On Wed, 2006-09-13 at 17:51 -0400, Vincent Levesque wrote:
> Hello all,
> 
> I ran into some problems after moving working code to a slower machine 
> and traced the problem down to the example attached at the bottom of 
> this email. I've been using rt_task_send() to implement the equivalent 
> of a function call, with an error code returned in the reply MCB's 
> opcode field. In the example below, I send a message and expect a "666" 
> opcode to be returned but I receive garbage at least on a few calls. The 
> problem seems to occur when 1) the update rate in the sender is too high 
> and 2) rt_task_send() has a timeout value (1 sec in the example.)  If I 
> increase MAIN_RATE_NS or set the TIMEOUT to TM_INFINITE everything seems 
> to be ok. I've been able to reproduce this problem with xenomai 2.2.2 
> (two PCs) and 2.1.3. In more complex versions of this code the reply 
> data buffers also seemed to be invalid or corrupted.
> 

Confirmed and reproduced, including over the simulator. The reason for
the invalid opcode is that rt_task_reply() signals an EXIO error, so the
return value is not filled in. The question is: why do we get this
error. More later.

> Looking at the docs, I'm not sure what to expect when rt_task_send() 
> times out. It is returning 0 here. If I understand correctly, there is 
> also no way to distinguish between an empty reply (with an opcode but no 
> data buffer) and a NULL reply (i.e. rt_task_reply(flowid, NULL)). Could 
> I be missing a rt_task_send() failure? If so, why would it fail here?
> 

rt_task_reply(flowid, NULL) would always force the opcode field to zero.
Therefore, you should use non-zero return codes for valid messages,
whether they are empty or not.

> Thanks,
> 
> Vincent Levesque
> vleves@domain.hid
> 
> gcc -o test main.c `/usr/xenomai-2.2/bin/xeno-config --xeno-cflags` 
> `/usr/xenomai-2.2/bin/xeno-config --xeno-ldflags` -lnative
> 
> #include <sys/mman.h>
> #include <native/task.h>
> 
> #define TIMEOUT ((RTIME)1E9)
> #define PEER_RATE_NS 100000
> #define MAIN_RATE_NS 5000000
> #define PEER_NB_ITER 50
> 
> void run_peer(void *arg)
> {
>     unsigned char buf[1024];
>     RT_TASK_MCB mcb_rcv, mcb_reply;
>     int flowid, i, rv;
> 
>     while (1)
>     {
>         mcb_rcv.data = (caddr_t)buf;
>         mcb_rcv.size = sizeof(buf);
>         flowid = rt_task_receive(&mcb_rcv,TM_INFINITE);
>         if(flowid >= 0)
>         {
>             rt_task_set_periodic(NULL,TM_NOW,PEER_RATE_NS);
>             for (i=0; i<PEER_NB_ITER; ++i)
>                 rt_task_wait_period(NULL);
>             rt_task_set_periodic(NULL,TM_NOW,TM_INFINITE);
> 
>             mcb_reply.opcode = 666;
>             mcb_reply.size = 0;
>             mcb_reply.data = NULL;
>             rt_task_reply(flowid, &mcb_reply);
>         }
>     }
> }
> 
> int main(int argc, char *argv[])
> {
>     int i, rv;
>     RT_TASK task, peer_task;
>     RT_TASK_MCB mcb_send, mcb_reply;
> 
>     mlockall(MCL_CURRENT | MCL_FUTURE);
> 
>     rt_task_spawn(&peer_task, "peer", 4096, 99, T_FPU, &run_peer, NULL);
>     rt_task_shadow(&task, "user", 50, 0);
>     
>     rt_task_set_periodic(NULL,TM_NOW,MAIN_RATE_NS);
> 
>     for (i=0; i<10; ++i)
>     {
>         rt_task_wait_period(NULL);
>         mcb_send.opcode = 0x02;
>         mcb_send.data = NULL;
>         mcb_send.size = 0;
>         mcb_reply.size = 0;
>         mcb_reply.data = NULL;
>         rv = rt_task_send(&peer_task,&mcb_send,&mcb_reply,TIMEOUT);
>         if (rv < 0) printf("rt_task_send error\n");
>         if (mcb_reply.opcode != 666)
>             printf("rv=%d, opcode=%d\n", rv, mcb_reply.opcode);
>     }
> 
>     rt_task_delete(&peer_task);
>     rt_task_delete(NULL);
> 
>     return 0;
> }
> 
> 
> 
> _______________________________________________
> Xenomai-help mailing list
> Xenomai-help@domain.hid
> https://mail.gna.org/listinfo/xenomai-help
-- 
Philippe.