PIC18 UART Driver

include/uart.h

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+#ifndef ROCKETLIB_UART_H
+#define ROCKETLIB_UART_H
+
+#include <stdbool.h>
+#include <stdint.h>
+
+#include "common.h"
+
+/*
+ * Initializes the UART1 module.
+ *
+ * baud_rate: Desired baud rate (e.g., 9600, 115200)
+ * fosc: Clock frequency (must be 12 MHz or 48 MHz)
+ * enable_flow_control: true to enable RTS flow control, false to disable
+ *
+ * Returns: W_SUCCESS if setup is successful, otherwise W_INVALID_PARAM
+ */
+w_status_t uart_init(uint32_t baud_rate, uint32_t fosc, bool enable_flow_control);
+
+/*
+ * Transmits a single byte over UART (blocking).
+ *
+ * waits until the transmit buffer is empty, then sends the byte.
+ */
+void uart_transmit_byte(uint8_t byte);
+// void uart_transmit_buffer(uint8_t *tx, uint8_t len);
+
+/*
+ * Interrupt handler for UART1.
+ *
+ * Handles RX and optional TX,
+ * and calls user-defined uart_rx_callback() on received bytes.
+ */
+void uart_interrupt_handler(void);
+
+/*
+ * Internal callback function called when a byte is received via UART1.
+ *
+ * This is implemented in uart.c and currently echoes the received byte back.
+ * It is not intended to be overridden by user code due to MPLAB limitations.
+ */
+void uart_rx_callback(uint8_t byte);
+
+#endif /* ROCKETLIB_UART_H */
+

pic18f26k83/uart.c

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+#include <stdbool.h>
+#include <stdint.h>
+#include <xc.h>
+
+#include "common.h"
+#include "uart.h"
+
+void uart_rx_callback(uint8_t byte) {
+    uart_transmit_byte(byte); // echos back recieved byte
+}
+
+w_status_t uart_init(uint32_t baud_rate, uint32_t fosc, bool enable_flow_control) {
+    // make sure to Configure UART1 pins before running!!!
+
+    // only 12 or 48 MHz support for pic
+    if (fosc != 12000000UL && fosc != 48000000UL) {
+        return W_INVALID_PARAM;
+    }
+
+    // bool controlled flow control.
+    U1CON2bits.FLO = enable_flow_control ? 0b10 : 0b00;
+
+    // low speed
+    U1CON0bits.BRGS = 0;
+    uint32_t divisor = (U1CON0bits.BRGS == 1) ? 4 : 16;
+
+    // checks for valid baud rate
+    if (baud_rate == 0 || baud_rate > (fosc / divisor)) {
+        return W_INVALID_PARAM;
+    }
+
+    // disable autodetect baudrate
+    U1CON0bits.ABDEN = 0;
+    // normal mode (8 bit, no parity, no 9th bit)
+    U1CON0bits.MODE = 0;
+    // enable transmit
+    U1CON0bits.TXEN = 1;
+    // enable receive
+    U1CON0bits.RXEN = 1;
+
+    // keep running on overflow, never stop receiving
+    U1CON2bits.RUNOVF = 1;
+
+    // dynamic baud rate
+    uint16_t brg = (fosc / (divisor * baud_rate)) - 1;
+    U1BRGH = (brg >> 8) & 0xFF;
+    U1BRGL = brg & 0xFF;
+
+    // enable UART module
+    U1CON1bits.ON = 1;
+
+    // enable receive interrupt
+    IPR3bits.U1RXIP = 1;
+    PIE3bits.U1RXIE = 1;
+
+    // do not enable TX interrupt initially; only needed when there's queued data
+
+    return W_SUCCESS;
+}
+
+void uart_transmit_byte(uint8_t byte) {
+    while (!PIR3bits.U1TXIF)
+        ; // blocking wait
+    U1TXB = byte;
+}
+
+void uart_interrupt_handler(void) {
+    // TX interrupt
+    if (PIR3bits.U1TXIF) {
+        PIR3bits.U1TXIF = 0;
+    }
+
+    // RX interrupt
+    if (PIR3bits.U1RXIF) {
+        PIR3bits.U1RXIF = 0;
+        uint8_t rcv = U1RXB;
+        uart_rx_callback(rcv); // invoke user callback
+    }
+
+    // UART error interrupt
+    if (PIR3bits.U1EIF) {
+        PIR3bits.U1EIF = 0;
+        // optionally handle framing/parity/overflow errors
+    }
+
+    // global UART interrupt
+    if (PIR3bits.U1IF) {
+        PIR3bits.U1IF = 0;
+    }
+}
+