From 2bce2c984a31ebcdf81f83e5b819192596cb6d0f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Xose=20P=C3=A9rez?= <xose.perez@gmail.com>
Date: Sat, 25 Nov 2017 10:07:49 +0100
Subject: [PATCH] Added I2C clean bus code

---
 code/espurna/i2c.ino | 105 +++++++++++++++++++++++++++++++++++++++----
 1 file changed, 96 insertions(+), 9 deletions(-)

diff --git a/code/espurna/i2c.ino b/code/espurna/i2c.ino
index 98499a9d..c5ccee82 100644
--- a/code/espurna/i2c.ino
+++ b/code/espurna/i2c.ino
@@ -10,33 +10,120 @@ Copyright (C) 2017 by Xose Pérez <xose dot perez at gmail dot com>
 
 #include "brzo_i2c.h"
 
+int _i2cClearbus(int sda, int scl) {
+
+    #if defined(TWCR) && defined(TWEN)
+        // Disable the Atmel 2-Wire interface so we can control the SDA and SCL pins directly
+        TWCR &= ~(_BV(TWEN));
+    #endif
+
+    // Make SDA (data) and SCL (clock) pins inputs with pullup
+    pinMode(sda, INPUT_PULLUP);
+    pinMode(scl, INPUT_PULLUP);
+
+    delay(2500);
+    // Wait 2.5 secs. This is strictly only necessary on the first power
+    // up of the DS3231 module to allow it to initialize properly,
+    // but is also assists in reliable programming of FioV3 boards as it gives the
+    // IDE a chance to start uploaded the program
+    // before existing sketch confuses the IDE by sending Serial data.
+
+    // If it is held low the device cannot become the I2C master
+    // I2C bus error. Could not clear SCL clock line held low
+    boolean scl_low = (digitalRead(scl) == LOW);
+    if (scl_low) return 1;
+
+
+    boolean sda_low = (digitalRead(sda) == LOW);
+    int clockCount = 20; // > 2x9 clock
+
+    // While SDA is low for at most 20 cycles
+    while (sda_low && (clockCount > 0)) {
+
+        clockCount--;
+
+        // Note: I2C bus is open collector so do NOT drive SCL or SDA high
+        pinMode(scl, INPUT);        // release SCL pullup so that when made output it will be LOW
+        pinMode(scl, OUTPUT);       // then clock SCL Low
+        delayMicroseconds(10);      // for >5uS
+        pinMode(scl, INPUT);        // release SCL LOW
+        pinMode(scl, INPUT_PULLUP); // turn on pullup resistors again
+                                    // do not force high as slave may be holding it low for clock stretching
+
+        delayMicroseconds(10);      // The >5uS is so that even the slowest I2C devices are handled
+
+        //  loop waiting for SCL to become high only wait 2sec
+        scl_low = (digitalRead(scl) == LOW);
+        int counter = 20;
+        while (scl_low && (counter > 0)) {
+            counter--;
+            delay(100);
+            scl_low = (digitalRead(scl) == LOW);
+        }
+
+        // If still low after 2 sec error
+        // I2C bus error. Could not clear. SCL clock line held low by slave clock stretch for >2sec
+        if (scl_low) return 2;
+
+        sda_low = (digitalRead(sda) == LOW); //   and check SDA input again and loop
+
+    }
+
+    // If still low
+    // I2C bus error. Could not clear. SDA data line held low
+    if (sda_low) return 3;
+
+    // Pull SDA line low for "start" or "repeated start"
+    pinMode(sda, INPUT);        // remove pullup
+    pinMode(sda, OUTPUT);       // and then make it LOW i.e. send an I2C Start or Repeated start control
+
+    // When there is only one I2C master a "start" or "repeat start" has the same function as a "stop" and clears the bus
+    // A Repeat Start is a Start occurring after a Start with no intervening Stop.
+
+    delayMicroseconds(10);      // wait >5uS
+    pinMode(sda, INPUT);        // remove output low
+    pinMode(sda, INPUT_PULLUP); // and make SDA high i.e. send I2C STOP control.
+
+    delayMicroseconds(10);      // wait >5uS
+    pinMode(sda, INPUT);        // and reset pins as tri-state inputs which is the default state on reset
+    pinMode(scl, INPUT);
+
+    // Everything OK
+    return 0;
+
+}
+
 bool i2cCheck(unsigned char address) {
     brzo_i2c_start_transaction(address, I2C_SCL_FREQUENCY);
     brzo_i2c_ACK_polling(1000);
     return brzo_i2c_end_transaction();
 }
 
-void i2cScan() {
+unsigned char i2cFind(size_t size, unsigned char * addresses) {
+    for (unsigned char i=0; i<size; i++) {
+        if (i2cCheck(addresses[i]) == 0) return addresses[i];
+    }
+    return 0;
+}
 
+void i2cScan() {
     unsigned char nDevices = 0;
-
-    for (unsigned char address = 1; address < 128; address++) {
-        unsigned char response = i2cCheck(address);
-        if (response == 0) {
+    for (unsigned char address = 1; address < 127; address++) {
+        unsigned char error = i2cCheck(address);
+        if (error == 0) {
             DEBUG_MSG_P(PSTR("[I2C] Device found at address 0x%02X\n"), address);
             nDevices++;
-        } else if (response != 32) {
+        } else if (error != 32) {
             //DEBUG_MSG_P(PSTR("[I2C] Unknown error at address 0x%02X\n"), address);
         }
     }
-
     if (nDevices == 0) DEBUG_MSG_P(PSTR("[I2C] No devices found\n"));
-
 }
 
 void i2cSetup() {
+    DEBUG_MSG_P(PSTR("[I2C] Using GPIO%d for SDA and GPIO%d for SCL\n"), I2C_SDA_PIN, I2C_SCL_PIN);
+    //DEBUG_MSG_P(PSTR("[I2C] Clear bus (response: %d)\n"), _i2cClearbus(I2C_SDA_PIN, I2C_SCL_PIN));
     brzo_i2c_setup(I2C_SDA_PIN, I2C_SCL_PIN, I2C_CLOCK_STRETCH_TIME);
-    i2cScan();
 }
 
 #endif