Implemented P-persistent CSMA in KISS mode

Modem/config.h

@@ -6,9 +6,13 @@
 #define PROTOCOL_SIMPLE_SERIAL 0x01
 #define PROTOCOL_KISS 0x02
 
+// Which serial protocol we want the modem to use
 #define SERIAL_PROTOCOL PROTOCOL_SIMPLE_SERIAL
 //#define SERIAL_PROTOCOL PROTOCOL_KISS
 
+// Enable P-persistent CSMA
+#define CSMA_ENABLE true
+
 // Debug & test options
 #define SERIAL_DEBUG false
 #define PASSALL true

Modem/main.c

@@ -103,7 +103,7 @@ static void init(void)
     
     #if SERIAL_PROTOCOL == PROTOCOL_KISS
         // Init KISS
-        kiss_init(&ax25, &ser);
+        kiss_init(&ax25, &afsk, &ser);
     #endif
     
     // That's all!

Modem/protocol/KISS.c

@@ -8,6 +8,7 @@
 
 static uint8_t serialBuffer[CONFIG_AX25_FRAME_BUF_LEN+1]; // Buffer for holding incoming serial data
 AX25Ctx *ax25ctx;
+Afsk *channel;
 Serial *serial;
 size_t frame_len;
 bool IN_FRAME;
@@ -16,9 +17,13 @@ uint8_t command = CMD_UNKNOWN;
 unsigned long custom_preamble = CONFIG_AFSK_PREAMBLE_LEN;
 unsigned long custom_tail = CONFIG_AFSK_TRAILER_LEN;
 
-void kiss_init(AX25Ctx *ax25, Serial *ser) {
+unsigned long slotTime = 200;
+uint8_t p = 63;
+
+void kiss_init(AX25Ctx *ax25, Afsk *afsk, Serial *ser) {
     ax25ctx = ax25;
     serial = ser;
+    channel = afsk;
 }
 
 void kiss_messageCallback(AX25Ctx *ctx) {
@@ -44,11 +49,39 @@ void fon(void) {
     while (ts--) PORTB |= BV(2);
 }
 
+void kiss_csma(AX25Ctx *ctx, uint8_t *buf, size_t len) {
+    bool sent = false;
+    while (!sent) {
+        if(!channel->hdlc.receiving) {
+            uint8_t tp = rand() & 0xFF;
+            if (tp < p) {
+                ax25_sendRaw(ctx, buf, len);
+                sent = true;
+            } else {
+                ticks_t start = timer_clock();
+                while (timer_clock() - start < ms_to_ticks(slotTime)) {
+                    cpu_relax();
+                }
+            }
+        } else {
+            while (channel->hdlc.receiving) {
+                cpu_relax();
+            }
+        }
+
+    }
+    
+}
+
 
 void kiss_serialCallback(uint8_t sbyte) {
     if (IN_FRAME && sbyte == FEND && command == CMD_DATA) {
         IN_FRAME = false;
-        ax25_sendRaw(ax25ctx, serialBuffer, frame_len);
+        #if CSMA_ENABLE
+            kiss_csma(ax25ctx, serialBuffer, frame_len);
+        #else
+            ax25_sendRaw(ax25ctx, serialBuffer, frame_len);
+        #endif
     } else if (sbyte == FEND) {
         IN_FRAME = true;
         command = CMD_UNKNOWN;
@@ -75,6 +108,10 @@ void kiss_serialCallback(uint8_t sbyte) {
             custom_preamble = sbyte * 10UL;
         } else if (command == CMD_TXTAIL) {
             custom_tail = sbyte * 10;
+        } else if (command == CMD_SLOTTIME) {
+            slotTime = sbyte * 10;
+        } else if (command == CMD_P) {
+            p = sbyte;
         } 
         
     }

Modem/protocol/KISS.h

@@ -18,9 +18,10 @@
 
 #include <net/ax25.h>
 #include <drv/ser.h>
+#include "afsk.h"
 
-void kiss_init(AX25Ctx *ax25, Serial *ser);
-
+void kiss_init(AX25Ctx *ax25, Afsk *afsk, Serial *ser);
+void kiss_csma(AX25Ctx *ctx, uint8_t *buf, size_t len);
 void kiss_messageCallback(AX25Ctx *ctx);
 void kiss_serialCallback(uint8_t sbyte);
 void fon(void);

buildrev.h

@@ -1,2 +1,2 @@
-#define VERS_BUILD 2367
+#define VERS_BUILD 2400
 #define VERS_HOST  "shard"