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Mailbox for transfer large amounts of data
Posted: Wed Nov 25, 2015 2:23 pm
by kab
Hello!
I'm using stm32f103ret6 custom board (running at 72 Mzh) and have question.
I need to transfer large amounts of data between ICU and thread, which parse this data.
I choose mailbox for that purpose.
I create interrupt handler for ICU using TIM4 (with frequency 1 mhz), which catch pulses width (minimal pulse width around 30-50 uS):
Code: Select all
static void icu_width_callback(ICUDriver *icup)
{
msg_t msg;
pulse_width = icuGetWidthX(icup);
msg = pulse_width;
chSysLockFromISR();
if (chMBPostI(&mailbox, msg)!=MSG_OK)
{
// mailbox full, switch led on
palSetPad(IOPORT2, GPIOB_LED);
}
chSysUnlockFromISR();
...
}
And also casual thread is created, which catch this data:
Code: Select all
static THD_FUNCTION(mParseThread, arg) {
(void) arg;
msg_t msg;
/* Thread loop, until terminated.*/
while (chThdShouldTerminateX() == false) {
/* Waiting for a message.*/
chMBFetch(&mailbox, &msg, TIME_INFINITE);
...
In general all working fine, but from time to time i have 'mailbox full' case.
So, my question is: is it good idea to use mailbox for fast trasfer between ISR and Thread or not?
May be simple shared circle buffer is better (less overhead)?
Re: Mailbox for transfer large amounts of data
Posted: Wed Nov 25, 2015 2:35 pm
by Giovanni
Hi,
Mailboxes are simple circular buffers
and are meant for ISR->Thread data exchange. Your use case is correct.
Is your thread at higher priority than other threads? scheduling could delay it enough to cause the overflow. You may also increase the mailbox size so you would have more buffer (size is not shown in your example).
Giovanni
Re: Mailbox for transfer large amounts of data
Posted: Wed Nov 25, 2015 3:01 pm
by kab
Hello!
Thanks for an answer! Seems that i'm on right way.
I've start with 256 msg_t buffer, but even 1024 did not helps, in some rare cases 'mailbox full led' is turn on.
Thread have normal prio, because there is also communication thread (usb now for debug, casual serial in real device) and i worry, that higher prio can block communication thread.
Total i have 4 threads:
* usb/serial for communication (i'm using simple shell from your example)
* ICU interrupt handler
* parser
* sleeping thread which blink another led on event
Also, i'm using tickless mode, but power saving is not important.
Re: Mailbox for transfer large amounts of data
Posted: Wed Nov 25, 2015 3:08 pm
by Giovanni
Hi,
Try putting it at highest priority, other threads should not be much affected. If a buffer of 1024 does not help then there is an issue with priorities, other threads are preventing it from empting the queue.
Giovanni
Re: Mailbox for transfer large amounts of data
Posted: Wed Nov 25, 2015 3:11 pm
by kab
Hello!
And which mode is faster (less overhead for switching) - tickless or casual?
Re: Mailbox for transfer large amounts of data
Posted: Wed Nov 25, 2015 3:50 pm
by Giovanni
No impact on switching. Tickless is only heavier on virtual timers and everything else is generally faster because much less interrupts are served.
Giovanni
Re: Mailbox for transfer large amounts of data
Posted: Wed Nov 25, 2015 5:50 pm
by kab
Hello!
Thanks again for detailed answers!
Will try to play with prio.
Re: Mailbox for transfer large amounts of data
Posted: Thu Dec 10, 2015 7:42 am
by samtatasurya
kab wrote:Hello!
Thanks again for detailed answers!
Will try to play with prio.
Hi kab,
I wonder if you have any update regarding your progress. I'm currently bump into similar problem in my system, so it'd be great if you can share your solution to this problem.
Thank you!
Re: Mailbox for transfer large amounts of data
Posted: Mon Dec 21, 2015 1:28 pm
by kab
Hi!
Giovanni tell everything, set prio to high and that's works.
I'm also lower frequency from 1 mhz to 500 khz (in my case this is acceptable).
However, all depends from your worker thread, if it make some huge calculations, some messages can be missed.
Re: Mailbox for transfer large amounts of data
Posted: Mon Dec 21, 2015 4:01 pm
by samtatasurya
Thanks for your reply!
Yes, after tracking down my issue, I found out that my worker thread delayed the acquisition from the mailbox.