sam3x8e: Add initial support for Arduino Due boards

This adds basic support for running on the Atmel SAM3x8e
micro-controllers that are found in the Arudino Due boards.

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

src/sam3x8e/serial.c

@@ -0,0 +1,148 @@
+// sam3x8e serial port
+//
+// Copyright (C) 2016  Kevin O'Connor <kevin@koconnor.net>
+//
+// This file may be distributed under the terms of the GNU GPLv3 license.
+
+#include <string.h> // memmove
+#include "autoconf.h" // CONFIG_SERIAL_BAUD
+#include "board/gpio.h" // gpio_peripheral
+#include "board/io.h" // readb
+#include "board/misc.h" // console_get_input
+#include "sam3x8e.h" // UART
+#include "sched.h" // DECL_INIT
+#include "irq.h" // irq_save
+
+#define SERIAL_BUFFER_SIZE 96
+static char receive_buf[SERIAL_BUFFER_SIZE];
+static uint32_t receive_pos;
+static char transmit_buf[SERIAL_BUFFER_SIZE];
+static uint32_t transmit_pos, transmit_max;
+
+
+/****************************************************************
+ * Serial hardware
+ ****************************************************************/
+
+static void
+serial_init(void)
+{
+    gpio_peripheral('A', PIO_PA8A_URXD, 'A', 1);
+    gpio_peripheral('A', PIO_PA9A_UTXD, 'A', 0);
+
+    // Reset uart
+    PMC->PMC_PCER0 = 1 << ID_UART;
+    UART->UART_PTCR = UART_PTCR_RXTDIS | UART_PTCR_TXTDIS;
+    UART->UART_CR = UART_CR_RSTRX | UART_CR_RSTTX | UART_CR_RXDIS | UART_CR_TXDIS;
+    UART->UART_IDR = 0xFFFFFFFF;
+
+    // Enable uart
+    UART->UART_MR = (US_MR_CHRL_8_BIT | US_MR_NBSTOP_1_BIT | UART_MR_PAR_NO
+                     | UART_MR_CHMODE_NORMAL);
+    UART->UART_BRGR = SystemCoreClock / (16 * CONFIG_SERIAL_BAUD);
+    UART->UART_IER = UART_IER_RXRDY;
+    NVIC_EnableIRQ(UART_IRQn);
+    NVIC_SetPriority(UART_IRQn, 0);
+    UART->UART_CR = UART_CR_RXEN | UART_CR_TXEN;
+}
+DECL_INIT(serial_init);
+
+void __visible
+UART_Handler(void)
+{
+    uint32_t status = UART->UART_SR;
+    if (status & UART_SR_RXRDY) {
+        uint8_t data = UART->UART_RHR;
+        if (receive_pos >= sizeof(receive_buf))
+            // Serial overflow - ignore it as crc error will force retransmit
+            return;
+        receive_buf[receive_pos++] = data;
+        return;
+    }
+    if (status & UART_SR_TXRDY) {
+        if (transmit_pos >= transmit_max)
+            UART->UART_IDR = UART_IDR_TXRDY;
+        else
+            UART->UART_THR = transmit_buf[transmit_pos++];
+    }
+}
+
+// Enable tx interrupts
+static void
+enable_tx_irq(void)
+{
+    UART->UART_IER = UART_IDR_TXRDY;
+}
+
+
+/****************************************************************
+ * 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)
+{
+    uint32_t copied = 0;
+    for (;;) {
+        uint32_t rpos = readb(&receive_pos);
+        uint32_t needcopy = rpos - len;
+        if (needcopy) {
+            memmove(&receive_buf[copied], &receive_buf[copied + len]
+                    , needcopy - copied);
+            copied = needcopy;
+        }
+        irqstatus_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)
+{
+    uint32_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);
+    enable_tx_irq();
+    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_irq();
+}