lnxknl4
commented
1 year ago Here is an example of implementing a custom protocol on STM32 to send and receive packetized messages with a host system:
// Packet structure
typedef struct {
uint8_t start_byte; // Start byte
uint8_t msg_len; // Message length
uint8_t msg_type; // Message type
uint8_t data[64]; // Message data
uint8_t crc; // CRC checksum
} packet_t;
// Function to calculate CRC uint8_t crc_calc(packet_t *pkt) { // CRC algorithm return crc; }
// Function to send packet void send_packet(packet_t *pkt) {
pkt->crc = crc_calc(pkt);
// Add start byte USART_SendData(START_BYTE);
// Send packet bytes over USART USART_SendData(pkt->msg_len); USART_SendData(pkt->msg_type); // etc... USART_SendData(pkt->crc); }
// Function to receive packet packet_t recv_packet() {
packet_t pkt;
// Wait for start byte while(USART_ReceiveData() != START_BYTE);
// Receive packet bytes pkt.msg_len = USART_ReceiveData(); pkt.msg_type = USART_ReceiveData(); // etc...
// Verify CRC if(pkt.crc != crc_calc(&pkt)) { // Error }
return pkt; }
// Create and send status packet packet_t pkt; pkt.msg_type = 1; // Status message
pkt.data[0] = 0x01; // Led on pkt.data[1] = 0x00; // Door closed pkt.data[2] = 23; // Room temp
send_packet(&pkt);
// Receive control packet packet_t ctrl_pkt = recv_packet();
if(ctrl_pkt.msg_type == 2) { // Control message
// Process data
if(ctrl_pkt.data[0]) {
// Turn on LED
}
}
This implements a basic protocol with packet formatting, checksum, message types, and data fields. The MCU can send status packets and receive control packets from a host system over USART.
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