From 78c1f77b87d657b0db961472be175a143fdc9c16 Mon Sep 17 00:00:00 2001
From: Stephan Richter <s.richter@srsoftware.de>
Date: Thu, 2 Nov 2023 01:02:51 +0100
Subject: [PATCH] re-implemented library. needs to be tested!

Signed-off-by: Stephan Richter <s.richter@srsoftware.de>
---
 SoftRS485.cpp                              | 250 +++++++++------------
 SoftRS485.h                                |   3 +-
 examples/SendAndReceive/SendAndReceive.ino |  45 +---
 3 files changed, 116 insertions(+), 182 deletions(-)

diff --git a/SoftRS485.cpp b/SoftRS485.cpp
index 3483bcf..ca68918 100644
--- a/SoftRS485.cpp
+++ b/SoftRS485.cpp
@@ -9,136 +9,50 @@
 //#define DEBUG
 #define MSG_LEN 64
 
-#define IDLE 0
-#define START 1
-#define RECEIVING 2
-#define SENDING 3
-#define COMPLETE 4
-
 // Pins
 int _RO, _RE, _DE, _DI;
-int _idle_cycles = 0;
+long _pulse_len = 100;
 
-/* INCOMING */
-char    _recv_message[MSG_LEN];
-byte    _recv_byte = 0x00;
-byte    _recv_state = IDLE;
+// Receive vars
 boolean _recv_bit = false;
-byte    _recv_idx = 0;
-int     _recv_pos = 0;
-
-
-
-/* OUTGOING */
-char _send_message[MSG_LEN];
-boolean _send_bit = false;
-byte _send_state = IDLE;
-byte _send_wait = 0;
-byte _send_idx = 0;
-int  _send_pos = 0;
-
-ISR(TIMER1_COMPA_vect){
-    OCR1A += 3228; // Advance The COMPA Register
-
-    if (_send_state == SENDING){
-        char c = _send_message[_send_pos];
-        _send_bit = c & 1<<_send_idx;
-        digitalWrite(_DI,!_send_bit);
-#ifdef DEBUG
-        Serial.print("Sending bit "); Serial.print(_send_idx); Serial.print(" of "); Serial.print(c); Serial.print(": "); Serial.print(_send_bit); Serial.print(" / ");
-#endif
-        _send_idx++;
-        if (_send_idx==8){ // byte completed
-            _send_pos++;  // advance to next byte
-            _send_idx = 0; // start with first bit
-            if (c == 0x00 || _send_idx == MSG_LEN){ // we just send a 0-byte
-                _send_state = COMPLETE;
-            }
-        }
-    }
-    if (_send_state == START && _idle_cycles > 9){
-        _send_bit = HIGH;
-        digitalWrite(_DE,HIGH);
-        digitalWrite(_DI,!_send_bit);
-        _send_state = SENDING;
-        _send_idx = 0;
-        _send_pos = 0;
+long _last_flip; // this is the time when the bus switched to logical zero
+byte _recv_msg[MSG_LEN];
+int _recv_pos = 0;
+int _recv_idx = 0;
+boolean _avail = false;
+
+void interrupt485(){
+    _recv_bit = !digitalRead(_RO); // HIGH level = logical zero and vice versa
+    long now = micros();
+    long diff = now - _last_flip;
+    _last_flip = now;
+    if (diff > 20*_pulse_len){ // we received a start bit
 #ifdef DEBUG
-        Serial.print("Sent start bit: "); Serial.print(_send_bit); Serial.print(" / ");
+        Serial.print(F("State changed to ")); Serial.println(_recv_bit);
+        Serial.println(F("received start bit"));
 #endif
-    }
-
-    _recv_bit = !digitalRead(_RO); // LOW = 1
-
-    if (_recv_bit) {
-        _idle_cycles = 0;
-    } else if (_idle_cycles<1000) {
-        _idle_cycles++;
-    }
-#ifdef DEBUG
-    Serial.print("idle cycles: "); Serial.print(_idle_cycles); Serial.print(" / ");
-    Serial.print("received: "); Serial.print(_recv_bit); Serial.print(" / ");
-#endif
-
-    if (_send_bit != _recv_bit && _send_state == SENDING){ // collision while sending
-        digitalWrite(_DE,LOW); // disable driver
-        _send_state = START;   // start over
-        _idle_cycles = 0;
-#ifdef DEBUG
-        Serial.println("\nCOLLISION");
-#endif
-    }
-
-    if (_send_state == COMPLETE){
-        digitalWrite(_DE,LOW); // disable driver
-        _send_message[0]=0x00; // clear message
-        _send_state = IDLE;
-        _idle_cycles =0;
-#ifdef DEBUG
-        Serial.print("transmission complete / ");
-#endif
-    }
-
-
-
-    if (_recv_state == START){
-        _recv_byte = 0x00;
         _recv_pos = 0;
         _recv_idx = 0;
-        _recv_state = RECEIVING;
-#ifdef DEBUG
-        Serial.print("Start reception / ");
-#endif
-    }
-
-    if (_recv_bit && _recv_state == IDLE){
-        _recv_state = START;
-    }
-
-    if (_recv_state == RECEIVING){
-        _recv_byte |= _recv_bit << _recv_idx;           // set bit
-        _recv_idx++;                                    // increase bit index
-        if (_recv_idx == 8){                            // byte full
-#ifdef DEBUG
-            Serial.print("pushing "); Serial.print((char)_recv_byte); Serial.print(" / ");
-#endif
-
-            _recv_message[_recv_pos] = _recv_byte;      // push character to string
-            if (_recv_byte == 0x00) {                   // end of message
-                _recv_state = IDLE;
-#ifdef DEBUG
-                Serial.print("reception complete: "); Serial.print(_recv_message);
-#endif
+        _last_flip+=_pulse_len;
+    } else {
+        long count = diff/_pulse_len;
+        for (int i=0; i<count; i++){
+            if (_recv_idx == 0) {
+                _recv_msg[_recv_pos] = (!_recv_bit);
+            } else {
+                _recv_msg[_recv_pos] |= (!_recv_bit)<<_recv_idx;
+            }
+            _recv_idx++;
+            if (_recv_idx == 8){
+                _recv_idx = 0;
+                if (_recv_msg[_recv_pos] == 0x00){
+                    _avail = _recv_pos != 0;
+                    return;
+                }
+                _recv_pos++;
             }
-            _recv_idx=0;                                // start new byte
-            _recv_byte = 0;
-            _recv_pos++;                                // goto next string pos
-            if (_recv_pos == MSG_LEN) _recv_pos--;      // avoid overflow
         }
     }
-#ifdef DEBUG
-    Serial.println();
-#endif
 }
 
 void init485(int RO, int nRE, int DE, int DI){
@@ -146,8 +60,7 @@ void init485(int RO, int nRE, int DE, int DI){
     _RE=nRE;
     _DE=DE;
     _DI=DI;
-    _recv_message[0] = 0x00; // empty
-    _send_message[0] = 0x00; // empty
+
     pinMode(_RO,INPUT);
 
     pinMode(_RE,OUTPUT);
@@ -159,46 +72,93 @@ void init485(int RO, int nRE, int DE, int DI){
     pinMode(_DI,OUTPUT);
     digitalWrite(_DI,LOW); // output line = LOW
 
-    TCCR1A = 0;           // Init Timer1A
-    TCCR1B = 0;           // Init Timer1B
-    TCCR1B |= B00000001;  // Prescaler = 1
-    OCR1A = 3328;        // Timer Compare1A Register
-    TIMSK1 |= B00000010;  // Enable Timer COMPA Interrupt
+    attachInterrupt(digitalPinToInterrupt(_RO),interrupt485,CHANGE);
+
 #ifdef DEBUG
     Serial.begin(115200);
-    Serial.println("Started timer!");
-    Serial.print("RO = ");
+    Serial.print(F("RO = "));
     Serial.println(_RO);
-    Serial.print("^RE = ");
+    Serial.print(F("^RE = "));
     Serial.println(_RE);
-    Serial.print("DE = ");
+    Serial.print(F("DE = "));
     Serial.println(_DE);
-    Serial.print("DI = ");
+    Serial.print(F("DI = "));
     Serial.println(_DI);
+#endif
+    _last_flip = micros();
+}
+
+void speed485(long baudrate){
+#ifndef DEBUG
+    _pulse_len = 1e6 / baudrate;
+#else
+    _pulse_len = 1000;
+    Serial.print(F("Set pulse_len to ")); Serial.print(_pulse_len); Serial.println(F("µs"));
 #endif
 }
 
 boolean available485(){
-    return _recv_state == IDLE && _recv_message[0] != 0;
+    return _avail;
 }
 
-String get485Message(){
-    String res = String(_recv_message);
-    _recv_message[0] = 0;
-    return res;
+String get485message(){
+    _avail = false;
+    return String((char*)_recv_msg);
 }
 
-boolean send485(char message[]){
-    if (_send_message[0] != 0x00) return false; // we already have a queued message, abort!
-    for (int idx = 0; idx<MSG_LEN; idx++){
-        _send_message[idx] = message[idx]; // copy message
-        if (message[idx] == 0x00) break;
+boolean writeBit(boolean bit){
+    digitalWrite(_DI,!bit);
+    delayMicroseconds(5);
+    if (_recv_bit != bit){ // collision!
+       digitalWrite(_DE,LOW);
+#ifdef DEBUG
+       Serial.println(F("Collision!"));
+#endif
+       return false;
     }
-    if (_send_message[0] == 0x00) return false; // message is empty! abort
-    _send_state = START;
+    delayMicroseconds(_pulse_len-5);
+    return true;
+}
 
+boolean send485(char message[]){
 #ifdef DEBUG
-    Serial.print("sending "); Serial.println(_send_message);
+    Serial.print(F("preparing to send "));
+    Serial.print(message);
+    Serial.print(F(": line state = "));
+    Serial.print(_recv_bit);
+    Serial.print(F(" / last_flip = "));
+    Serial.print(_last_flip);
+    Serial.print(F(" / micros = "));
+    Serial.println(micros());
 #endif
-    return true;
+    while (_recv_bit || (micros() - _last_flip) < (20 * _pulse_len)) {
+        delayMicroseconds(20*_pulse_len);
+    }
+#ifdef DEBUG
+    Serial.println(F("enabling driver…"));
+#endif
+    digitalWrite(_DE,HIGH); // enable driver
+    if (!writeBit(HIGH)) return false;
+    int pos = -1;
+    boolean good = true;
+    do {
+        pos++;
+#ifdef DEBUG
+        Serial.print(F("sending character ")); Serial.println(message[pos]);
+#endif
+        good = writeBit(message[pos] & 0x01)
+            && writeBit(message[pos] & 0x02)
+            && writeBit(message[pos] & 0x04)
+            && writeBit(message[pos] & 0x08)
+            && writeBit(message[pos] & 0x10)
+            && writeBit(message[pos] & 0x20)
+            && writeBit(message[pos] & 0x40)
+            && writeBit(message[pos] & 0x80);
+    } while (good && message[pos]);
+    if (good) writeBit(1);
+    digitalWrite(_DE,LOW); // disable driver
+#ifdef DEBUG
+    Serial.println(F("disabled driver…"));
+#endif
+    return good;
 }
diff --git a/SoftRS485.h b/SoftRS485.h
index 5df46e1..daf9344 100644
--- a/SoftRS485.h
+++ b/SoftRS485.h
@@ -9,7 +9,8 @@
 #include "Arduino.h"
 
 extern void init485(int RO, int nRE, int DE, int DI);
+extern void speed485(long pulse_length);
 extern boolean available485();
-extern String get485Message();
+extern String get485message();
 extern boolean send485(char message[]);
 #endif
diff --git a/examples/SendAndReceive/SendAndReceive.ino b/examples/SendAndReceive/SendAndReceive.ino
index 0d6aefa..5ad30b7 100644
--- a/examples/SendAndReceive/SendAndReceive.ino
+++ b/examples/SendAndReceive/SendAndReceive.ino
@@ -1,45 +1,18 @@
-/*
- 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!");
+  init485(2,3,4,5);
+  speed485(8000);
+  boolean sent = false;
+  while (!sent) {
+    sent = send485("This message is sent and received!");
   }
 }
 
-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);
-    if (!send485(msg)){
-      Serial.print("Sending ");
-      Serial.print(msg);
-      Serial.println(" failed!");
-    }
+void loop() {
+  // put your main code here, to run repeatedly:
+  if (available485()){
+    Serial.println("Received "+get485message());
   }
 }