Initial commit of source code.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

src/avr/serial.c

@@ -0,0 +1,137 @@
+// AVR serial port code.
+//
+// Copyright (C) 2016  Kevin O'Connor <kevin@koconnor.net>
+//
+// This file may be distributed under the terms of the GNU GPLv3 license.
+
+#include <avr/interrupt.h> // USART0_RX_vect
+#include <string.h> // memmove
+#include "autoconf.h" // CONFIG_SERIAL_BAUD
+#include "sched.h" // DECL_INIT
+#include "irq.h" // irq_save
+#include "misc.h" // console_get_input
+
+#define SERIAL_BUFFER_SIZE 96
+static char receive_buf[SERIAL_BUFFER_SIZE];
+static uint8_t receive_pos;
+static char transmit_buf[SERIAL_BUFFER_SIZE];
+static uint8_t transmit_pos, transmit_max;
+
+
+/****************************************************************
+ * Serial hardware
+ ****************************************************************/
+
+static void
+serial_init(void)
+{
+    if (CONFIG_SERIAL_BAUD_U2X) {
+        UCSR0A = 1<<U2X0;
+        UBRR0 = DIV_ROUND_CLOSEST(F_CPU, 8UL * CONFIG_SERIAL_BAUD) - 1UL;
+    } else {
+        UCSR0A = 0;
+        UBRR0 = DIV_ROUND_CLOSEST(F_CPU, 16UL * CONFIG_SERIAL_BAUD) - 1UL;
+    }
+
+    UCSR0C = (1<<UCSZ01) | (1<<UCSZ00);
+    UCSR0B = (1<<RXEN0) | (1<<TXEN0) | (1<<RXCIE0) | (1<<UDRIE0);
+}
+DECL_INIT(serial_init);
+
+#ifdef USART_RX_vect
+#define USART0_RX_vect USART_RX_vect
+#define USART0_UDRE_vect USART_UDRE_vect
+#endif
+
+// Rx interrupt - data available to be read.
+ISR(USART0_RX_vect)
+{
+    uint8_t data = UDR0;
+    if (receive_pos >= sizeof(receive_buf))
+        // Serial overflow - ignore it as crc error will force retransmit
+        return;
+    receive_buf[receive_pos++] = data;
+}
+
+// Tx interrupt - data can be written to serial.
+ISR(USART0_UDRE_vect)
+{
+    if (transmit_pos >= transmit_max)
+        UCSR0B &= ~(1<<UDRIE0);
+    else
+        UDR0 = transmit_buf[transmit_pos++];
+}
+
+
+/****************************************************************
+ * Console access functions
+ ****************************************************************/
+
+// Return a buffer (and length) containing any incoming messages
+char *
+console_get_input(uint8_t *plen)
+{
+    *plen = readb(&receive_pos);
+    return receive_buf;
+}
+
+// Remove from the receive buffer the given number of bytes
+void
+console_pop_input(uint8_t len)
+{
+    uint8_t copied = 0;
+    for (;;) {
+        uint8_t rpos = readb(&receive_pos);
+        uint8_t needcopy = rpos - len;
+        if (needcopy) {
+            memmove(&receive_buf[copied], &receive_buf[copied + len]
+                    , needcopy - copied);
+            copied = needcopy;
+        }
+        uint8_t flag = irq_save();
+        if (rpos != readb(&receive_pos)) {
+            // Raced with irq handler - retry
+            irq_restore(flag);
+            continue;
+        }
+        receive_pos = needcopy;
+        irq_restore(flag);
+        break;
+    }
+}
+
+// Return an output buffer that the caller may fill with transmit messages
+char *
+console_get_output(uint8_t len)
+{
+    uint8_t tpos = readb(&transmit_pos), tmax = readb(&transmit_max);
+    if (tpos == tmax) {
+        tpos = tmax = 0;
+        writeb(&transmit_max, 0);
+        writeb(&transmit_pos, 0);
+    }
+    if (tmax + len <= sizeof(transmit_buf))
+        return &transmit_buf[tmax];
+    if (tmax - tpos + len > sizeof(transmit_buf))
+        return NULL;
+    // Disable TX irq and move buffer
+    writeb(&transmit_max, 0);
+    barrier();
+    tpos = readb(&transmit_pos);
+    tmax -= tpos;
+    memmove(&transmit_buf[0], &transmit_buf[tpos], tmax);
+    writeb(&transmit_pos, 0);
+    barrier();
+    writeb(&transmit_max, tmax);
+    UCSR0B |= 1<<UDRIE0;
+    return &transmit_buf[tmax];
+}
+
+// Accept the given number of bytes added to the transmit buffer
+void
+console_push_output(uint8_t len)
+{
+    writeb(&transmit_max, readb(&transmit_max) + len);
+    // enable TX interrupt
+    UCSR0B |= 1<<UDRIE0;
+}