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Rui Loureiro
Rui Loureiro
Associate II
June 14, 2017
Question

Correct way to send CAN message inside interrupt

  • June 14, 2017
  • 5 replies
  • 1725 views
Posted on June 14, 2017 at 12:45

I'm using an STM32F4 Discovery and an MCP2562 transceiver. I have CAN working using the CAN2 port.

In my implementation, I'm sending several CAN messages inside a timer interrupt. I'm using the HAL function HAL_CAN_TRANSMIT_IT.  It works fine until I try to send 3 or more messages in a row, in that case HAL_CAN_TRANSMIT_IT returns an error. How should I work around this?

I thought about using HAL_CAN_TRANSMIT, which has the option to use a timeout, but since this is called inside an interrupt, this should be avoided.

Any help will be greatly appreciated.

#hal #can #stm32f4-discovery
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5 replies

Nicolas Cmb
Nicolas Cmb
Associate III
June 14, 2017
Posted on June 14, 2017 at 13:23

Hi

Loureiro.Rui

,

Did you try to see some exmples on theSTM32_F4_*** files, wich probably has projects using the CAN communication ?

Regards ,

Nicolas

Kraal
Senior III
June 14, 2017
Posted on June 14, 2017 at 13:34

Hi !

I can't comment on the F4 but if the peripheral is the same as F0, then you have only 3 Tx mailboxes. So if you want to send more than 3 CAN messages in a row, you can either poll the mailboxes until one becomes free again or use a circular buffer with interrupts if you don't want to waste CPU cycles.

Nicolas Cmb
Nicolas Cmb
Associate III
June 14, 2017
Posted on June 14, 2017 at 13:55

I'm using the STM32F1 family and it's the same things (3 Tx Mailboxes), so maybe the STM32 F4 has the same abilities.

AvaTar
AvaTar
Senior III
June 14, 2017
Posted on June 14, 2017 at 14:24

Didn't check it, but I'm pretty sure it's the same peripheral.

IMHO another case where the Cube SW structure clashes with the application requirements.

I would organize CAN send receive and send in a SW queue, and just trigger the send from an interrupt (i.e. setting a flag for the queue to start the send).

The queue could be polled/processed at regular intervals (timer interrupt), or event driven, depending on your requirements.

Advantage is, this SW queue can be arbitrary long, not restricted to the implemented hardware.

I have no implementation for STM32 here, though.

Jeroen3
Jeroen3
Senior
June 15, 2017
Posted on June 15, 2017 at 09:31

Add more mailboxes in software. See if there are any software mailboxes marked for transmit on tx complete irq.

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