first working implementation of timer-based RS485

Signed-off-by: Stephan Richter <s.richter@srsoftware.de>

SoftRS485.cpp

@@ -6,30 +6,183 @@
 #include "Arduino.h"
 #include "SoftRS485.h"
 
-SoftRS485 SoftRS485::instance;
+//#define DEBUG
+#define IDLE -1
+#define START -2
+#define MSG_LEN 64
+
+int _RO, _RE, _DE, _DI;
+
+/* INCOMING */
+byte _recv_byte = 0x0;
+boolean _recv_bit = false;
+char _recv_message[MSG_LEN];
+int _recv_idx = 0; // used as bit-index for _recv_byte
+int _recv_pos = IDLE; // used as char-index for _recv_message
+
+/* OUTGOING */
+char _message_out[MSG_LEN];
+int _send_pos = IDLE;
+int _send_idx = 0;
+
+ISR(TIMER1_COMPA_vect){
+    OCR1A += 62500; // Advance The COMPA Register
+
+    _recv_bit = !digitalRead(_RO); // input line is HIGH by default
+    if (_recv_pos == IDLE){
+        if (_recv_bit) { // first 1 indicates incoming message
+            _recv_pos = 0;
+#ifdef DEBUG
+            Serial.println(F("start of message reception"));
+#endif
+        }
+    } else { // we are reading!
+        _recv_byte |= _recv_bit << _recv_idx;
+#ifdef DEBUG
+        Serial.print(F("received bit #"));
+        Serial.print(_recv_idx);
+        Serial.print(": ");
+        Serial.println(_recv_bit);
+        Serial.print(F("byte is now "));
+        Serial.println(_recv_byte,BIN);
+#endif
+        if (_recv_idx == 7){ // byte complete
+#ifdef DEBUG
+            Serial.print(F("byte complete: "));
+            Serial.println(_recv_byte);
+#endif
+            _recv_idx = 0;
+            _recv_message[_recv_pos] = _recv_byte;
+            if (_recv_byte == 0x00){ // we encountered a 0-byte! End of message!
+#ifdef DEBUG
+                Serial.print(F("got 0-byte!\nmessage reception complete: "));
+                Serial.println(_recv_message);
+#endif
+                _recv_idx = 0;
+                _recv_pos = IDLE;
+            } else {
+                _recv_byte = 0x00;
+                if (_recv_pos<MSG_LEN-1) {
+                    _recv_pos++;
+                }
+            }
+        } else _recv_idx++;
+    }
+
+    boolean bit = LOW;
+
+    if (_send_pos >= 0){
+        char c = _message_out[_send_pos];
+        if (c == 0x00) { // end of message
+            digitalWrite(_DI,HIGH);
+            digitalWrite(_DE,LOW);
+            _send_pos = IDLE;
+            _send_idx = 0;
+            _message_out[0] = 0x00;
+#ifdef DEBUG
+            Serial.println("Message transmission completed!");
+#endif
+        } else {
+            bit = !(c & 1<<_send_idx);
+            digitalWrite(_DI,bit);
+#ifdef DEBUG
+            Serial.print("Sending bit #");
+            Serial.print(_send_idx);
+            Serial.print(" (");
+            Serial.print(bit);
+            Serial.print(") of ");
+            Serial.print(c);
+            Serial.print(" (");
+            Serial.print(c,BIN);
+            Serial.println(")");
+#endif
+            _send_idx++;
+            if (_send_idx>7){
+                _send_idx =0;
+                _send_pos++;
+            }
+        }
+    }
+
+    if (_send_pos == START && _recv_pos == IDLE && _message_out[0] != 0x00) { // outgoig message awaits, line is idle
+        digitalWrite(_DE,HIGH); // enable driver
+#ifdef DEBUG
+        Serial.println(F("starting transmission"));
+#endif
+        digitalWrite(_DI,bit); // send start bit
+        _send_pos = 0;
+    }
+
+    if (_send_pos != IDLE && digitalRead(_RO) != bit){ // driver output state mismatch!
+        digitalWrite(_DE,LOW); // disable driver
+        _send_pos = START;
+#ifdef DEBUG
+        Serial.println(F("collision!"));
+#endif
+    }
 
-SoftRS485 SoftRS485::singleton(){
-    return instance;
-}
 
-void SoftRS485::isr(){
-    instance.bam();
 }
 
-void SoftRS485::begin(int RO, int nRE, int DE, int DI){
-  _RO = RO;
-  _RE = nRE;
-  _DE = DE;
-  _DI = DI;
+void init485(int RO, int nRE, int DE, int DI){
+    _RO=RO;
+    _RE=nRE;
+    _DE=DE;
+    _DI=DI;
+    _recv_message[0] = 0x00; // empty
+    _message_out[0] = 0x00; // empty
+    pinMode(_RO,INPUT);
+
+    pinMode(_RE,OUTPUT);
+    digitalWrite(_RE,LOW); // enable reading
+
+    pinMode(_DE,OUTPUT);
+    digitalWrite(_DE,LOW); // disable writing
+
+    pinMode(_DI,OUTPUT);
+    digitalWrite(_DI,LOW); // output line = LOW
+
+    TCCR1A = 0;           // Init Timer1A
+    TCCR1B = 0;           // Init Timer1B
+    TCCR1B |= B00000001;  // Prescaler = 512
+    OCR1A = 500;        // Timer Compare1A Register
+    TIMSK1 |= B00000010;  // Enable Timer COMPA Interrupt
+#ifdef DEBUG
     Serial.begin(115200);
-  pinMode(_RE, OUTPUT);
-  pinMode(_DE, OUTPUT);
-  pinMode(_DI, OUTPUT);
-  pinMode(_RO, INPUT);
-  attachInterrupt(digitalPinToInterrupt(_RO),isr,CHANGE);
-  Serial.println("attached to interrupt!");
+    Serial.println("Started timer!");
+    Serial.print("RO = ");
+    Serial.println(_RO);
+    Serial.print("^RE = ");
+    Serial.println(_RE);
+    Serial.print("DE = ");
+    Serial.println(_DE);
+    Serial.print("DI = ");
+    Serial.println(_DI);
+#endif
 }
 
-void SoftRS485::bam(){
-    Serial.println("bam!");
+boolean available485(){
+    return _recv_pos == IDLE && _recv_message[0] != 0;
+}
+
+String get485Message(){
+    String res = String(_recv_message);
+    _recv_message[0] = 0;
+    return res;
+}
+
+boolean send485(char message[]){
+    if (_message_out[0] != 0x00) return false; // we already have a queued message, abort!
+    for (int idx = 0; idx<MSG_LEN; idx++){
+        _message_out[idx] = message[idx]; // copy message
+        if (message[idx] == 0x00) break;
+    }
+    if (_message_out[0] == 0x00) return false; // message is empty! abort
+    _send_pos = START;
+
+#ifdef DEBUG
+    Serial.print("sending ");
+    Serial.println(_message_out);
+#endif
+    return true;
 }

SoftRS485.h

@@ -8,15 +8,8 @@
 
 #include "Arduino.h"
 
-class SoftRS485{
-  public:
-    void begin(int RO, int nRE, int DE, int DI);
-    void bam();
-    static SoftRS485 singleton();
-  private:
-    static void isr();
-    static SoftRS485 instance;
-    int _RO, _RE, _DE, _DI;
-};
-
+extern void init485(int RO, int nRE, int DE, int DI);
+extern boolean available485();
+extern String get485Message();
+extern boolean send485(char message[]);
 #endif

examples/SendAndReceive/SendAndReceive.ino

@@ -0,0 +1,44 @@
+/*
+ This sketch demonstrates, how to use the SoftRS485 library.
+ This library makes use of Arduinos timer 1
+ */
+
+#include <SoftRS485.h>
+
+int count = 0;
+String message = "Message ";
+
+void setup() {
+  Serial.begin(115200);
+
+  init485(2,3,4,5); // library initialization:
+  // connect pin 2 to RO of Max485
+  // connect pin 3 to ^RE of Max485
+  // connect pin 4 to DE of Max485
+  // connect pin 5 to DI of Max485
+
+  if (send485("Test")) {
+    // This should send "Test" if the line is free.
+    Serial.println("Test sent!");
+  }
+  if (!send485("Test2")) {
+    // This shoult fail, as transmission of "Test" should still be on the way
+    Serial.println("Test2 failed!");
+  }
+}
+
+void messageReceived(String message){
+}
+
+void loop(){
+  if (available485()){ // check if we have received anything
+    Serial.print("messageReceived: ");
+    Serial.println(get485Message()); // read the received message
+
+    // send another message everytime we have received one
+    count++;
+    char msg[128];
+    (message+count).toCharArray(msg,128);
+    send485(msg);
+  }
+}