From d79c4c3a209e09757c3b0bb541e21eabd52ad6e5 Mon Sep 17 00:00:00 2001
From: Stephan Richter <s.richter@srsoftware.de>
Date: Mon, 13 Nov 2023 08:22:23 +0100
Subject: [PATCH] Reverted back to delay-based send. Seems to work with single
 master. Needs to be tested in multi-drop environment

Signed-off-by: Stephan Richter <s.richter@srsoftware.de>
---
 SoftRS485.cpp | 211 ++++++++++++--------------------------------------
 SoftRS485.h   |   2 +-
 2 files changed, 52 insertions(+), 161 deletions(-)

diff --git a/SoftRS485.cpp b/SoftRS485.cpp
index 3339dfb..2ecb200 100644
--- a/SoftRS485.cpp
+++ b/SoftRS485.cpp
@@ -7,18 +7,11 @@
 #include "SoftRS485.h"
 
 //#define DEBUG
-
 #define MSG_LEN 64
-#define IDLE 0
-#define WAIT 1
-#define SEND 2
-#define SENT 3
 
-#define TIMER 250
 // Pins
 int _RO, _RE, _DE, _DI;
-long _pulse_len = 850;
-
+long _pulse_len = 105;
 
 // Receive vars
 boolean _recv_bit = false;
@@ -28,28 +21,6 @@ int _recv_pos = 0;
 int _recv_idx = 0;
 boolean _avail = false;
 
-// Send vars
-char _send_message[MSG_LEN];
-int _send_state = IDLE;
-int _send_pos = 0;
-int _send_idx = 0;
-boolean _send_bit = false;
-
-void enableSendTimer(){
-#ifdef DEBUG
-    Serial.print(F("Enabling send timer. Old Value: b"));
-    Serial.println(TIMSK1,BIN);
-#endif
-    TIMSK1 |= B00000010;  // Enable Timer COMPA Interrupt
-}
-
-void disableSendTimer(){
-#ifdef DEBUG
-    Serial.println("Disable send timer");
-#endif
-    TIMSK1 = TIMSK1 & ~B00000010;  // Enable Timer COMPA Interrupt
-}
-
 void interrupt485(){
     _recv_bit = !digitalRead(_RO); // HIGH level = logical zero and vice versa
     long now = micros();
@@ -57,36 +28,22 @@ void interrupt485(){
     _last_flip = now;
     if (diff > 20*_pulse_len){ // we received a start bit
 #ifdef DEBUG
+        Serial.print(F("State changed to ")); Serial.println(_recv_bit);
         Serial.println(F("received start bit"));
 #endif
         _recv_pos = 0;
         _recv_idx = 0;
         _last_flip+=_pulse_len;
     } else {
-#ifdef DEBUG
-        Serial.print(diff);
-        Serial.println("µs");
-#endif
-
         long count = diff/_pulse_len;
         for (int i=0; i<count; i++){
-#ifdef DEBUG
-            Serial.print(_recv_bit);
-            Serial.println(" <=");
-#endif
             if (_recv_idx == 0) {
-                _recv_msg[_recv_pos] = (_recv_bit);
+                _recv_msg[_recv_pos] = (!_recv_bit);
             } else {
-                _recv_msg[_recv_pos] |= (_recv_bit)<<_recv_idx;
+                _recv_msg[_recv_pos] |= (!_recv_bit)<<_recv_idx;
             }
             _recv_idx++;
             if (_recv_idx == 8){
-#ifdef DEBUG
-                Serial.print("0x");
-                Serial.print(_recv_msg[_recv_pos],HEX);
-                Serial.print(" recevied / ");
-                Serial.println((char)_recv_msg[_recv_pos]);
-#endif
                 _recv_idx = 0;
                 if (_recv_msg[_recv_pos] == 0x00){
                     _avail = _recv_pos != 0;
@@ -98,102 +55,6 @@ void interrupt485(){
     }
 }
 
-ISR(TIMER1_COMPA_vect){
-    OCR1A += TIMER; // Advance The COMPA Register
-
-    boolean echo = digitalRead(_RO);
-
-    if (_send_state == SENT){
-        if (echo != _send_bit){
-            digitalWrite(_DE,LOW);
-            _send_state = WAIT;
-#ifdef DEBUG
-            Serial.println(F("Collision"));
-#endif
-        } else {
-            digitalWrite(_DE,LOW);
-            _send_message[0] = 0x00;
-            _send_state = IDLE;
-            disableSendTimer();
-#ifdef DEBUG
-            Serial.println(F("Transmission complete"));
-#endif
-        }
-        return;
-    }
-
-    if (_send_state == SEND){
-        if (echo != _send_bit){
-            digitalWrite(_DE,LOW);
-            _send_state = WAIT;
-    #ifdef DEBUG
-            Serial.println(F("Collision"));
-    #endif
-            return;
-        }
-
-        char c = _send_message[_send_pos];
-        _send_bit = c & (1 << _send_idx);
-        digitalWrite(_DI,_send_bit);
-
-#ifdef DEBUG
-        if (!_send_idx) {
-            Serial.print("Sending "); Serial.print(c); Serial.print(" / 0x"); Serial.println(c,HEX);
-        }
-        Serial.print("<--- "); Serial.println(_send_bit);
-#endif
-        _send_idx++;
-        if (_send_idx == 8) {
-            _send_idx = 0;
-            _send_pos++;
-            if (c == 0x00 || _send_pos == MSG_LEN){
-                _send_state = SENT;
-            }
-        }
-    }
-
-    if (_send_state == WAIT){
-        long diff = micros() - _last_flip; // µs
-        long idle_count = diff / _pulse_len;
-        if (idle_count > MSG_LEN){
-            _send_bit = LOW;
-            digitalWrite(_DE,HIGH);
-            digitalWrite(_DI,_send_bit);
-            _send_state = SEND;
-            _send_idx = 0;
-            _send_pos = 0;
-#ifdef DEBUG
-            Serial.println(F("Sending start bit (1)"));
-#endif
-        } else {
-#ifdef DEBUG
-            Serial.println(F("Bus busy"));
-#endif
-            return;
-        }
-    }
-
-    echo = digitalRead(_RO);
-    if (echo != _send_bit){
-        digitalWrite(_DE,LOW);
-        _send_state = WAIT;
-#ifdef DEBUG
-        Serial.println(F("Collision"));
-#endif
-        return;
-    }
-
-}
-
-void configureSendTimer(){
-    TCCR1A = 0;           // Init Timer1A
-    TCCR1B = 0;           // Init Timer1B
-    TCCR1B |= B00000011;  // Prescaler = 1
-    OCR1A = TIMER;        // Timer Compare1A Register
-}
-
-
-
 void init485(int RO, int nRE, int DE, int DI){
     _RO=RO;
     _RE=nRE;
@@ -212,7 +73,7 @@ void init485(int RO, int nRE, int DE, int DI){
     digitalWrite(_DI,LOW); // output line = LOW
 
     attachInterrupt(digitalPinToInterrupt(_RO),interrupt485,CHANGE);
-    configureSendTimer();
+
 #ifdef DEBUG
     Serial.begin(115200);
     Serial.print(F("RO = "));
@@ -236,29 +97,59 @@ String get485message(){
     return String((char*)_recv_msg);
 }
 
-
-boolean send485(String message){
-    if (_send_message[0] != 0x00) {
+boolean writeBit(boolean bit){
+    digitalWrite(_DI,!bit);
+    delayMicroseconds(5);
+    if (_recv_bit != bit){ // collision!
+       digitalWrite(_DE,LOW);
 #ifdef DEBUG
-        Serial.println("Busy!");
+       Serial.println(F("Collision!"));
 #endif
-        return false; // we already have a queued message, abort!
+       return false;
     }
+    delayMicroseconds(_pulse_len-12);
+    return true;
+}
 
+boolean send485(char message[]){
 #ifdef DEBUG
-    Serial.print(F("Preparing to send ")); Serial.println(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
-    const char* buf = message.c_str();
-    for (int idx = 0; idx<MSG_LEN; idx++){
-        _send_message[idx] = buf[idx]; // copy message
-        if (_send_message[idx] == 0x00) break;
+    while (_recv_bit || (micros() - _last_flip) < (20 * _pulse_len)) {
+        delayMicroseconds(20*_pulse_len);
     }
-    if (_send_message[0] == 0x00) return false; // message is empty
 #ifdef DEBUG
-    Serial.print(F("Message copied to send buffer: "));
-    Serial.println(_send_message);
+    Serial.println(F("enabling driver…"));
 #endif
-    _send_state = WAIT;
-    enableSendTimer();
-    return true;
+    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 4b6b1cf..70e7d0b 100644
--- a/SoftRS485.h
+++ b/SoftRS485.h
@@ -11,5 +11,5 @@
 extern void init485(int RO, int nRE, int DE, int DI);
 extern boolean available485();
 extern String get485message();
-extern boolean send485(String message);
+extern boolean send485(char message[]);
 #endif