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Description
I have two devices connected by a CAN
line, based on SN65HVD230DR
.
One device, let's call it device B
, transmits CORRECTION_ID
to the CAN
bus, device B
also receives data on the CORRECTION_ID
change via the CAN
line and writes it to the EEPROM
, after the CORRECTION_ID
has changed in the EEPROM
, it starts transmitting the updated value to the CAN
bus.
Here we are not interested in device B
, we are more interested in device A
, which receives the CORRECTION_ID
value via the CAN
bus and displays it on the display.
Device A
is based on the esp32
and uses the esp32_can
library for the CAN
bus.
The code for reading the CAN0
bus is as follows:
CAN_FRAME message;
void printCANFrame(CAN_FRAME &frame) {
if (frame.id == CORRECTION_ID) {
if (frame.length == 8) {
CORR_ID= (static_cast<int>(frame.data.uint8[2]) << 8) |
(static_cast<int>(frame.data.uint8[1]));
}
}
void canTask(void *pvParameters) {
Serial.println("Start CAN bus setup");
CAN0.setCANPins(GPIO_NUM_21, GPIO_NUM_18);
if(CAN0.begin(500000))
{
Serial.println("Builtin CAN Init OK");
} else {
Serial.println("BuiltIn CAN Init Failed");
}
CAN0.watchFor(CORRECTION_ID, 0x7FF);
Serial.println("CAN bus Ready");
while (true) {
if (CAN0.read(message)) {
printCANFrame(message);
}
vTaskDelay(2 / portTICK_PERIOD_MS);
}
}
void setup()
{
xTaskCreate(canTask, "CAN Task", 2048 + 1024, NULL, 2, &canTaskHandle);
}
void loop()
{
}
This code perfectly receives and filters messages from the CAN
broadcast bus and on the display of the device A
I see the value CORRECTION_ID
.
Now I needed to send an updated value of CORRECTION_ID
from device A
to the CAN
bus.
The code is as follows:
if (CAN0.read(message)) {
frame_tx.id = CORRECTION_ID;
frame_tx.length = 3;
frame_tx.extended = false;
frame_tx.data.uint8[0] = 0x00;
frame_tx.data.uint8[1] = CORR_ID;
frame_tx.data.uint8[2] = CORR_ID>> 8;
CAN0.sendFrame(message);
printCANFrame(message);
}
But after loading such code into device A,
it stops receiving anything from the CAN
bus, and does not transmit anything to the CAN
bus either.
Consider this code as pseudo-code
😀
I understand that in the while (true) {}
loop, data will be transmitted and received to the CAN
bus almost simultaneously, but I tried adding millis, like in the example:
In general, for some reason, there are no normal modern examples for the esp32_can
library, there are many examples in the due_can
library, but they also cannot boast of completeness and novelty.
It would be great to update the examples or fill the WIKI
, without this the library is very difficult to use🙄