PIC18 UART Driver

include/uart.h

@@ -0,0 +1,43 @@
+#ifndef ROCKETLIB_UART_H
+#define ROCKETLIB_UART_H
+
+#include <stdbool.h>
+#include <stdint.h>
+
+#include "common.h"
+
+/*
+ * Initialize UART module. Set up rx and tx buffers, set up module,
+ * and enable the requisite interrupts
+ */
+w_status_t uart_init(uint32_t baud_rate, uint32_t fosc, bool enable_flow_control);
+
+/*
+ * A lot like transmitting a single byte, except there are multiple bytes. tx does
+ * not need to be null terminated, that's why we have the len parameter
+ *
+ * tx: pointer to an array of bytes to send
+ * len: the number of bytes that should be sent from that array
+ */
+void uart_transmit_buffer(uint8_t *tx, uint8_t len);
+
+/*
+ * returns true if there's a byte waiting to be read from the UART module
+ */
+bool uart_byte_available(void);
+
+/*
+ * pops a byte from the receive buffer and returns it. Don't call this
+ * function unless uart_byte_available is returning true. Don't call this
+ * function from an interrupt context.
+ */
+uint8_t uart_read_byte(void);
+
+/*
+ * handler for all UART1 module interrputs. That is, PIR3:U1IF, U1EIF, U1TXIF, and U1RXIF
+ * this function clears the bits in PIR3 that it handles.
+ */
+void uart_interrupt_handler(void);
+
+#endif /* ROCKETLIB_UART_H */
+

pic18f26k83/uart.c

@@ -0,0 +1,122 @@
+#include <pic18f26k83.h>
+#include <stdbool.h>
+#include <stdint.h>
+
+#include "canlib.h"
+#include "canlib/util/safe_ring_buffer.h"
+#include "common.h"
+#include "uart.h"
+
+// safe ring buffers for sending and receiving
+static srb_ctx_t rx_buffer;
+static srb_ctx_t tx_buffer;
+
+// memory pools to use for those srbs. 100 is a completely arbitrary number
+uint8_t rx_buffer_pool[100], tx_buffer_pool[100];
+
+w_status_t uart_init(uint32_t baud_rate, uint32_t fosc, bool enable_flow_control) {
+    // only 12 or 48 MHz 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 if baud rate param within range
+    if (baud_rate == 0 || baud_rate > (fosc / divisor)) {
+        return W_INVALID_PARAM;
+    }
+
+    // don't 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;
+
+    // we are go for UART
+    U1CON1bits.ON = 1;
+
+    // initialize the rx and tx buffers
+    srb_init(&rx_buffer, rx_buffer_pool, sizeof(rx_buffer_pool), sizeof(uint8_t));
+    srb_init(&tx_buffer, tx_buffer_pool, sizeof(tx_buffer_pool), sizeof(uint8_t));
+
+    // enable receive interrupt
+    IPR3bits.U1RXIP = 1;
+    PIE3bits.U1RXIE = 1;
+    // Do not enable transmit interrupt, that interrupt enable signals that
+    // there is data to be sent, which at init time is not true
+
+    return W_SUCCESS;
+}
+
+void uart_transmit_buffer(uint8_t *tx, uint8_t len) {
+    // just call uart_transmit_byte with each byte they want us to send
+    while (len--) {
+        srb_push(&tx_buffer, tx);
+        tx++;
+    }
+    // If the module isn't enabled, give it a byte to send and enable it
+    if (PIE3bits.U1TXIE == 0) {
+        srb_pop(&tx_buffer, &tx);
+        U1TXB = tx;
+        U1CON0bits.TXEN = 1;
+        // also enable the interrupt for when it's ready to send more data
+        PIE3bits.U1TXIE = 1;
+    }
+}
+
+bool uart_byte_available(void) {
+    return !srb_is_empty(&rx_buffer);
+}
+
+uint8_t uart_read_byte(void) {
+    uint8_t rcv;
+    srb_pop(&rx_buffer, &rcv);
+    return rcv;
+}
+
+void uart_interrupt_handler(void) {
+    if (PIR3bits.U1TXIF) {
+        // check if there are any bytes we still want to transmit
+        if (!srb_is_empty(&tx_buffer)) {
+            // if so, transmit them
+            uint8_t tx;
+            srb_pop(&tx_buffer, &tx);
+            U1TXB = tx;
+        } else {
+            // If we have no data to send, disable this interrupt
+            PIE3bits.U1TXIE = 0;
+            // if not, disable the TX part of the uart module so that TXIF
+            // isn't triggered again and so that we reenable the module on
+            // the next call to uart_transmit_byte
+            U1CON0bits.TXEN = 0;
+        }
+        PIR3bits.U1TXIF = 0;
+    } else if (PIR3bits.U1RXIF) {
+        // we received a byte, need to push into RX buffer and return
+        uint8_t rcv = U1RXB;
+        srb_push(&rx_buffer, &rcv);
+        PIR3bits.U1RXIF = 0;
+    } else if (PIR3bits.U1EIF) {
+        // Some sort of error, ignore for now (TODO?)
+        PIR3bits.U1EIF = 0;
+    } else if (PIR3bits.U1IF) {
+        PIR3bits.U1IF = 0;
+    }
+}