Rebroadcasting existing CAN msg on network issue

[pulsar]

I'm working with an existing CAN network on which I want to read a msg, modify it slightly and rebroadcast.

I'm running into an issue where the code seems to crash/freeze if I broadcast the new message too close to the original one thats on the network.

Inside HAL_CAN_RxFifo0MsgPendingCallback() I listen for the msg I want to modify and do a HAL_CAN_AddTxMessage() call as soon as it arrives with the updated msg data.  This seems to be working fine. 

I then want to repeat identical msg just before the next time the original msg is broadcast on the network which is on a 30ms interval.  I use HAL_GetTick() to track when the last msg was received inside HAL_CAN_RxFifo0MsgPendingCallback() and then in the main while(1) loop again I use HAL_GetTick() to count down the ms to just before the next msg is expected to be and do a HAL_CAN_AddTxMessage() with the custom data.  This seems to be working fine unless I get within 4ms of the original msg at which point everything hangs.  I'd like to get as close as possible to the original msg.

Any suggestion how I can accomplish this or a better way of doing it?  I cannot modify the original CAN network, I can only read and broadcast messages.

[SofLit]

Hello @pulsar and welcome to the community,

Need to share your code to understand what you are intending to do.

[pulsar]

So this code is very crude...

void HAL_CAN_RxFifo0MsgPendingCallback_(CAN_HandleTypeDef *hcan_)
{
	HAL_CAN_GetRxMessage(&hcan, CAN_RX_FIFO0, &RxHeader, (uint8_t*)RxData);

	if(RxHeader.StdId == 0x250)
	{
		RxData[0] = 0;
		HAL_CAN_AddTxMessage(&hcan, &TxHeader, (uint8_t*)RxData, &TxMailbox);
		last_received_tick = HAL_GetTick();
		process_msg = 1;
	}
}

while (1)
{
	if (process_msg && (HAL_GetTick() - last_received_tick) >= 27) {
		HAL_CAN_AddTxMessage(&hcan, &TxHeader, (uint8_t*)our_msg, &TxMailbox);
		process_msg = 0;
	}
}

[SofLit]

Sorry I didn't understand this statement:

---

@pulsar wrote:

This seems to be working fine unless I get within 4ms of the original msg at which point everything hangs.  I'd like to get as close as possible to the original msg.

---

I think better to put a sketch or figure of what your program is intended to work and what the problem is ... 

[pulsar]

I'm listing to an existing network for a specific msg id which is broadcast on 30ms interval. When that message is detected/received, I want to right away broadcast my own msg that's on the same id. Then I want to repeat this custom message broadcast before the next original version is broadcast on the network, as late as possible before its next 30ms cycle.