1 files changed, 61 insertions, 0 deletions
diff --git a/arduino/ace_old/physical.c b/arduino/ace_old/physical.c
new file mode 100644
index 0000000..17e15d7
--- /dev/null
+++ b/arduino/ace_old/physical.c
@@ -0,0 +1,61 @@
+#include "physical.h"
+#include "link.h"
+
+#include <avr/interrupt.h>
+
+typedef struct {
+  uint8_t buffer[SERIAL_BUFFER_SIZE];
+  volatile uint16_t head;
+  volatile uint16_t tail;
+} ring_buffer;
+
+static ring_buffer tx_buffer = {{0}, 0, 0};
+
+
+void init_physical_layer(uint32_t baud) {
+  //enable double speed transmission
+  UCSR0A |= (1 << U2X0);
+
+  uint16_t baud_setting = (F_CPU / 4 / baud - 1) / 2;
+  // assign the baud_setting, a.k.a. ubbr (USART Baud Rate Register)
+  UBRR0H = baud_setting >> 8;
+  UBRR0L = baud_setting;
+  
+  // defaults to 8-bit, no parity, 1 stop bit
+  UCSR0B |= (1 << RXEN0) | (1 << TXEN0) | (1 << RXCIE0);
+  UCSR0B &= ~(1 << UDRIE0) | (1 << TXEN0) | (1 << RXCIE0);
+}
+
+
+//receive
+ISR(USART0_RX_vect) {
+  uint8_t c = UDR0;
+  from_physical_layer(c);
+}
+
+//data register empty
+ISR(USART0_UDRE_vect) {
+  if (tx_buffer.head == tx_buffer.tail) {
+    //buffer empty, disable interruot
+    UCSR0B &= ~(1 << UDRIE0);
+  } else {
+    uint8_t c = tx_buffer.buffer[tx_buffer.tail];
+    tx_buffer.tail = (tx_buffer.tail + 1) % SERIAL_BUFFER_SIZE;
+    UDR0 = c; //write next byte
+  }
+}
+
+void to_physical_layer(uint8_t byte) {
+  uint16_t i = (tx_buffer.head + 1) % SERIAL_BUFFER_SIZE;
+	
+  // If the output buffer is full, there's nothing for it other than to 
+  // wait for the interrupt handler to empty it a bit
+if (i == tx_buffer.tail) return;
+  //while (i == tx_buffer.tail) {};
+	
+  tx_buffer.buffer[tx_buffer.head] = byte;
+  tx_buffer.head = i;
+	
+	//enable data register empty interrupt
+	UCSR0B |= (1 << UDRIE0);
+};