From e15a7e1267a6f733d734c5d3b59f3acc28bb4b29 Mon Sep 17 00:00:00 2001
From: Jakob Odersky <jodersky@gmail.com>
Date: Mon, 25 Feb 2013 19:39:53 +0100
Subject: initial commit

---
 arduino/ace/arq.c | 122 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 122 insertions(+)
 create mode 100644 arduino/ace/arq.c

(limited to 'arduino/ace/arq.c')

diff --git a/arduino/ace/arq.c b/arduino/ace/arq.c
new file mode 100644
index 0000000..9d4a08c
--- /dev/null
+++ b/arduino/ace/arq.c
@@ -0,0 +1,122 @@
+#include "arq.h"
+
+#include <stdlib.h>
+/* Expected frame data for ARQ
+ * 
+ * +-----+-----+------+
+ * | seq | cmd | data |
+ * +-----+-----+------+
+ * 
+ * seq: sequence number of frame (1 byte)
+ * cmd: command id of frame (1 byte), currently either ACK or DATA
+ * data: actual data of frame (arbitraty length, respecting frame limitations)
+ * 
+ * Note: frame checking, headers and footers are not handled by arq, see 'framing' instead
+ *
+*/
+
+#define MAX_RESENDS 5 //number of resends before a timeout is generated
+#define MAX_SEQ 255 //maximum sequence number of frames
+#define DATA 0x05
+#define ACK 0x06
+
+#define SEQ_INDEX 0
+#define CMD_INDEX 1
+#define MESSAGE_OFFSET 2
+#define MAX_MESSAGE_SIZE MAX_FRAME_SIZE - MESSAGE_OFFSET
+
+
+typedef enum {
+  RECEIVED_FRAME,
+  TIMEOUT
+} arq_event;
+
+static void send_ack(arq* a, uint8_t seq) {
+  uint8_t data[] = {seq, ACK};
+  a->sender(2, data);
+}
+
+static void process_event(arq* a, arq_event event, int16_t data_size, uint8_t* data) {
+  if (event == RECEIVED_FRAME) {
+    uint8_t seq = data[SEQ_INDEX];
+    uint8_t cmd = data[CMD_INDEX];
+    uint8_t* message = &(data[MESSAGE_OFFSET]);
+    int16_t message_size = data_size - MESSAGE_OFFSET;
+    
+    if (!a->awaiting_ack) { //ready to receive
+      if (cmd == DATA) {
+        if (a->last_received_seq != seq) {
+          a->last_received_seq = seq;
+          a->event_handler(RECEIVED, message_size, message);
+        }
+        send_ack(a, seq);
+      }
+      //ignore case in which an ack is received even though none is awaited
+    } else { //awaiting ack
+      a->awaiting_ack = false;
+       a->stop_timer();
+      
+      if (cmd == ACK && seq == a->last_sent_buffer[SEQ_INDEX]) {
+        a->event_handler(SEND_SUCCESS, a->last_sent_size - MESSAGE_OFFSET, &(a->last_sent_buffer[MESSAGE_OFFSET]));
+      } else {
+        a->event_handler(BAD_ACK, a->last_sent_size - MESSAGE_OFFSET, &(a->last_sent_buffer[MESSAGE_OFFSET]));
+      }
+    }
+    
+  } else if (event == TIMEOUT) {
+    if (a->resends > MAX_RESENDS) {
+      a->awaiting_ack = false;
+      a->stop_timer();
+      a->event_handler(NO_ACK, a->last_sent_size - MESSAGE_OFFSET, &(a->last_sent_buffer[MESSAGE_OFFSET]));
+    } else {
+      a->resends += 1;
+      a->sender(a->last_sent_size, a->last_sent_buffer);
+      a->awaiting_ack = true;
+      a->start_timer();
+    } 
+  }
+}
+
+void receive_frame(arq* a, int16_t size, uint8_t* data) {
+  process_event(a, RECEIVED_FRAME, size, data);
+}
+
+void timeout(arq* a) {
+  process_event(a, TIMEOUT, 0, NULL);
+}
+
+void send_message(arq* a, int16_t size, const uint8_t * const message) {
+  if (a->awaiting_ack) {
+    a->event_handler(BUSY, size, message);
+    return;
+  }
+  
+  if (size > MAX_MESSAGE_SIZE) {
+    a->event_handler(SIZE_ERROR, size, message);
+    return;
+  }
+    
+  
+  a->last_sent_buffer[SEQ_INDEX] += 1; //increment seq
+  a->last_sent_buffer[CMD_INDEX] = DATA;
+  int i;
+  for (i = 0; i < size; ++i) {
+    a->last_sent_buffer[i + MESSAGE_OFFSET] = message[i];
+  }
+  
+  a->last_sent_size = MESSAGE_OFFSET + size;
+  
+  a->sender(a->last_sent_size, a->last_sent_buffer);
+  a->awaiting_ack = true;
+  a->resends = 0;
+  a->start_timer();
+}
+
+void init_arq(arq* a) {
+  a->last_sent_size = 0;
+  a->last_received_seq = 0;
+  a->resends = 0;
+  a->awaiting_ack = false;
+}
+
+
-- 
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