Hey folks. So for a beginner DIY fixed-wing flight controller, I am trying to incorporate servo values from an external receiver via SBUS [by FrSky (0-> Low, 1-> High; contrary to the standard SBUS by Futaba)] into my software.
I found a good amount of code for the sum frame decoding, but appear to not receive any UART communication at all from the receiver.
A UART RX Callback function generates an interrupt whenever there's a new frame received. The function is supposed to write a message via another UART to my Putty-terminal (which works fine), upon calling.
Further into it, the SBUS frame gets torn apart and the individual channel values generated - but I'm not even at this stage, and by the looks of it, it should work fine. My code:
/* Private user code ---------------------------------------------------------*/
/* USER CODE BEGIN 0 */
uint16_t failsafe_status;
uint8_t buf[25];
uint16_t CH[18];
int lenght=0;
uint16_t USB_Send_Data[]={0};
char msg[25];
void HAL_UART_RxCpltCallback(UART_HandleTypeDef *huart1)
{
sprintf(msg, "FRAME AQCUIRED\r\n");
HAL_UART_Transmit(&huart2, (uint8_t*)msg, strlen(msg), HAL_MAX_DELAY);
if (buf[0] == 0x0F) {
CH[0] = (buf[1] >> 0 | (buf[2] << 8)) & 0x07FF;
CH[1] = (buf[2] >> 3 | (buf[3] << 5)) & 0x07FF;
CH[2] = (buf[3] >> 6 | (buf[4] << 2) | buf[5] << 10) & 0x07FF;
CH[3] = (buf[5] >> 1 | (buf[6] << 7)) & 0x07FF;
CH[4] = (buf[6] >> 4 | (buf[7] << 4)) & 0x07FF;
CH[5] = (buf[7] >> 7 | (buf[8] << 1) | buf[9] << 9) & 0x07FF;
CH[6] = (buf[9] >> 2 | (buf[10] << 6)) & 0x07FF;
CH[7] = (buf[10] >> 5 | (buf[11] << 3)) & 0x07FF;
CH[8] = (buf[12] << 0 | (buf[13] << 8)) & 0x07FF;
CH[9] = (buf[13] >> 3 | (buf[14] << 5)) & 0x07FF;
CH[10] = (buf[14] >> 6 | (buf[15] << 2) | buf[16] << 10) & 0x07FF;
CH[11] = (buf[16] >> 1 | (buf[17] << 7)) & 0x07FF;
CH[12] = (buf[17] >> 4 | (buf[18] << 4)) & 0x07FF;
CH[13] = (buf[18] >> 7 | (buf[19] << 1) | buf[20] << 9) & 0x07FF;
CH[14] = (buf[20] >> 2 | (buf[21] << 6)) & 0x07FF;
CH[15] = (buf[21] >> 5 | (buf[22] << 3)) & 0x07FF;
if (buf[23] & (1 << 0)) {
CH[16] = 1;
} else {
CH[16] = 0;
}
if (buf[23] & (1 << 1)) {
CH[17] = 1;
} else {
CH[17] = 0;
}
// Failsafe
failsafe_status = SBUS_SIGNAL_OK;
if (buf[23] & (1 << 2)) {
failsafe_status = SBUS_SIGNAL_LOST;
}
if (buf[23] & (1 << 3)) {
failsafe_status = SBUS_SIGNAL_FAILSAFE;
}
// SBUS_footer=buf[24];
}
}
/* USER CODE END 0 */This snippet is not mine, and I've got the feeling that the translation from the values into the buffer is missing. Could that be? If so, how would that look? To keep things simple I would like to avoid DMA in the beginning.
The while-loop is basically just the channel values 1-6 being printed to the serial terminal repeatedly.
CONCLUSION: Since the serial communication itself works, but neither gets any values nor notifies for a new frame, I think the issue lies within the SBUS -> UART part of it. Means, the Callback doesnt get executed for whatever reason. Additionally, here's my .ioc:
Iv'e tried it with 9 or 8 bits word length, but that doesnt change anything. Since FrSky is using the Inverted-SBUS, which is inverted itself (0->H, 1->L), I figured the data polarity is correct aswell as the jumper wires and config settings on the RX.
Regarding the transfer to the buffer AND/OR the Callback, what are your thoughts?
Thank you for explaining how to use the Interrupt structure, I think I understood it a little deeper now. Out of curiosity, is there a document that explains the functionalities and especially their structures (when to incorporate what or which purpose) of the HAL library a little better than the "Description of STM32F4 HAL and low-layer drivers (UM1725)" ? Had several issues when it comes to applying stuff I read in there.
Moving on - I copied your code, inserted my conversion snippet and tried it out:
It seems like most of the time, nothing changed too much - it's still picking up mostly random values. But by moving the sticks on the transmitter, I can occasionally (and not repeatedly) provoke a "valid" frame that leads to conversion and value output. To be fair, that worked before, too.
What I don't understand is this: SBUS is originally "inverted" to 1=LOW (confirmed by two independent sources, yet another one says the opposite). FrSky apparently chose to invert SBUS again to what I figure is 1=HIGH. As per definition, UART is 1=HIGH aswell so I should not need an inverter. It seems like the MCU does receive frames via UART, it just somehow is missing the "00001111" flag as Byte1 of the frame or buf[0] in my code. Is there anything to this I am still missing?
A variant that doesn't check for the start flag and just converts the input to its according SBUS values doesnt give me conclusive behavior:
If filtered by buf[0]=0x0F, the occasional result yields no better values.
Is it maybe signal degradation due to the baud rate being 100k and the bread-board cable I use between the Rx and the STM32 being 20cm long?
Am I totally wrong about UART and indeed do need to use an inverter?
