1 files changed, 103 insertions, 0 deletions
diff --git a/kernel/io/usart.c b/kernel/io/usart.c
new file mode 100644
index 0000000..2046630
--- /dev/null
+++ b/kernel/io/usart.c
@@ -0,0 +1,103 @@
+
+#include <stddef.h>
+#include <stdio.h>
+#include <avr/interrupt.h>
+#include "task/sched.h"
+#include "io/usart.h"
+#include "bug/debug.h"
+#include "mcu/task/context.h"
+
+static struct usart_device_t umain = USART_DEVICE_INIT(umain);
+static int umain_putc(char c);
+static int umain_getc();
+
+FILE umain_out = FDEV_SETUP_STREAM(umain_putc, NULL, _FDEV_SETUP_WRITE);
+FILE umain_in = FDEV_SETUP_STREAM(NULL, umain_getc, _FDEV_SETUP_READ);
+
+void usart_init(unsigned long baud) {
+  UCSR0A |= (1 << U2X0);   //enable double speed transmission
+  uint16_t baud_setting = (F_CPU / 4 / baud - 1) / 2;
+  UBRR0H = baud_setting >> 8;
+  UBRR0L = baud_setting;
+  UCSR0B |= (1 << RXEN0) | (1 << TXEN0) | (1 << RXCIE0); // 8-bit, no parity, 1 stop bit
+  UCSR0B &= ~(1 << UDRIE0);
+  stdout = &umain_out;
+  stdin = &umain_in;
+}
+
+int umain_putc(char c) {
+  if (c == '\n') umain_putc('\r');
+  int r = 0;
+  do {
+    cli();
+    r = rbuffer_write_char(&umain.tx_buffer, c);
+    sei();
+    UCSR0B |= (1 << UDRIE0);
+  } while (r != 1);
+  return c;
+}
+
+int umain_getc() {
+  while (rbuffer_empty(&umain.rx_buffer)) {
+    cli();
+    sleep_queue(&umain.rx_queue);
+    yield();
+  }
+  cli();
+  char c = 0;
+  size_t r = rbuffer_read_char(&umain.rx_buffer, &c);
+  sei();
+  if (r) return (int) c;
+  else return EOF;
+}
+
+//called when byte is received
+ISR(USART0_RX_vect, ISR_NAKED) {
+  context_save();
+  char c = UDR0;
+  rbuffer_write_char(&umain.rx_buffer, c);
+  wake_all_queue(&umain.rx_queue);
+  context_restore();
+  asm volatile ("reti");
+}
+
+//called when data register is empty
+ISR(USART0_UDRE_vect) {
+  char c;
+  if (rbuffer_read_char(&umain.tx_buffer, &c)) {
+    UDR0 = c;
+  } else {
+    UCSR0B &= ~(1 << UDRIE0); //buffer empty, disable interruot
+  }
+}
+
+/*
+void serial_read() {
+  ENTER_CRITICAL();
+  list_move_tail(&current->list, &serial_rx_q);
+  EXIT_CRITICAL();
+  yield();
+}
+*/
+/*
+void serial_write_str(const char* const str) {
+  for (size_t i = 0; str[i] != '\0'; ++i) {
+    ENTER_CRITICAL();
+    rbuffer_write(&serial_dev.tx_buffer, str[i]);
+    EXIT_CRITICAL();
+    UCSR0B |= (1 << UDRIE0);
+  }
+}*/
+
+
+/*
+ISR(INT3_vect, ISR_NAKED) {
+  SAVE_CONTEXT();
+  if (!list_empty(&serial_rx_q)) {
+    list_move_tail(serial_rx_q.next, &ready);
+  }
+  schedule();
+  RESTORE_CONTEXT();
+  asm volatile ("reti");
+}
+*/