avr: Initial support for Atmel AT90USB1286 mcu

Add GPIO definitions for the AT90USB1286.  Add code for communicating
over USB port on AT90USB1286.

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

src/avr/usbserial.c

@@ -0,0 +1,65 @@
+// Wrappers for AVR usb serial.
+//
+// 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 "../lib/pjrc_usb_serial/usb_serial.h"
+#include "sched.h" // DECL_INIT
+
+#define USBSERIAL_BUFFER_SIZE 64
+static char receive_buf[USBSERIAL_BUFFER_SIZE];
+static uint8_t receive_pos;
+static char transmit_buf[USBSERIAL_BUFFER_SIZE];
+
+static void
+usbserial_init(void)
+{
+    usb_init();
+}
+DECL_INIT(usbserial_init);
+
+// Return a buffer (and length) containing any incoming messages
+char *
+console_get_input(uint8_t *plen)
+{
+    for (;;) {
+        if (receive_pos >= sizeof(receive_buf))
+            break;
+        int16_t ret = usb_serial_getchar();
+        if (ret == -1)
+            break;
+        receive_buf[receive_pos++] = ret;
+    }
+    *plen = receive_pos;
+    return receive_buf;
+}
+
+// Remove from the receive buffer the given number of bytes
+void
+console_pop_input(uint8_t len)
+{
+    uint8_t needcopy = receive_pos - len;
+    if (needcopy)
+        memmove(receive_buf, &receive_buf[len], needcopy);
+    receive_pos = needcopy;
+}
+
+// Return an output buffer that the caller may fill with transmit messages
+char *
+console_get_output(uint8_t len)
+{
+    if (len > sizeof(transmit_buf))
+        return NULL;
+    return transmit_buf;
+}
+
+// Accept the given number of bytes added to the transmit buffer
+void
+console_push_output(uint8_t len)
+{
+    usb_serial_write((void*)transmit_buf, len);
+    usb_serial_flush_output();
+}