Add I2C support functions

Add new read/write functions to I2CManager class, and modify the LCD, OLED and PWM classes to use them effectively.

I2CManager.cpp

@@ -17,6 +17,8 @@
  *  along with CommandStation.  If not, see <https://www.gnu.org/licenses/>.
  */
 
+#include <stdarg.h>
+#include <Wire.h>
 #include "I2CManager.h"
 
 // If not already initialised, initialise I2C (wire).
@@ -48,10 +50,80 @@ void I2CManagerClass::forceClock(uint32_t speed) {
 
 // Check if specified I2C address is responding.
 // Returns 0 if OK, or error code.
-uint8_t I2CManagerClass::exists(uint8_t address) {
+uint8_t I2CManagerClass::checkAddress(uint8_t address) {
   begin();
   Wire.beginTransmission(address);
   return Wire.endTransmission();
 }
 
+bool I2CManagerClass::exists(uint8_t address) {
+  return checkAddress(address)==0;
+}
+
+// Write a complete transmission to I2C using a supplied buffer of data
+uint8_t I2CManagerClass::write(uint8_t address, const uint8_t buffer[], uint8_t size) {
+  Wire.beginTransmission(address);
+  Wire.write(buffer, size);
+  return Wire.endTransmission();
+}
+
+// Write a complete transmission to I2C using a supplied buffer of data in Flash
+uint8_t I2CManagerClass::write_P(uint8_t address, const uint8_t buffer[], uint8_t size) {
+  uint8_t ramBuffer[size];
+  memcpy_P(ramBuffer, buffer, size);
+  return write(address, ramBuffer, size);
+}
+  
+
+// Write a complete transmission to I2C using a list of data 
+uint8_t I2CManagerClass::write(uint8_t address, int nBytes, ...) {
+  uint8_t buffer[nBytes];
+  va_list args;
+  va_start(args, nBytes);
+  for (uint8_t i=0; i<nBytes; i++)
+    buffer[i] = va_arg(args, int);
+  va_end(args);
+  return write(address, buffer, nBytes);
+}
+
+// Write a command and read response, returns number of bytes received.
+//  Different modules use different ways of accessing registers: 
+//    PCF8574 I/O expander justs needs the address (no data);
+//    PCA9685 needs a two byte command to select the register(s) to be read;
+//    MCP23016 needs a one-byte command to select the register.
+// Some devices use 8-bit registers exclusively and some have 16-bit registers.
+// Therefore the following function is general purpose, to apply to any
+// type of I2C device.
+//
+uint8_t I2CManagerClass::read(uint8_t address, uint8_t readBuffer[], uint8_t readSize,
+                              uint8_t writeBuffer[], uint8_t writeSize) {
+  if (writeSize > 0) {
+    Wire.beginTransmission(address);
+    Wire.write(writeBuffer, writeSize);
+    Wire.endTransmission(false); // Don't free bus yet
+  }
+  Wire.requestFrom(address, readSize);
+  uint8_t nBytes = 0;
+  while (Wire.available() && nBytes < readSize) 
+    readBuffer[nBytes++] = Wire.read();
+  return nBytes;
+}
+
+// Overload of read() to allow command to be specified as a series of bytes.
+uint8_t I2CManagerClass::read(uint8_t address, uint8_t readBuffer[], uint8_t readSize, 
+                                  uint8_t writeSize, ...) {
+  va_list args;
+  // Copy the series of bytes into an array.
+  va_start(args, writeSize);
+  uint8_t writeBuffer[writeSize];
+  for (uint8_t i=0; i<writeSize; i++)
+    writeBuffer[i] = va_arg(args, int);
+  va_end(args);
+  return read(address, readBuffer, readSize, writeBuffer, writeSize);
+}
+
+uint8_t I2CManagerClass::read(uint8_t address, uint8_t readBuffer[], uint8_t readSize) {
+  return read(address, readBuffer, readSize, NULL, 0);
+}
+
 I2CManagerClass I2CManager = I2CManagerClass();