add I2C library

pic/MDR/I2C.c

@@ -0,0 +1,161 @@
+/* software bit banging implementation
+ * based on https://en.wikipedia.org/wiki/I2c example code
+ */
+#include "I2C.h"
+
+// Hardware-specific support functions that MUST be customized:
+#define I2CSPEED 100
+void I2C_delay()
+{
+	volatile int v = 0;
+	int i;
+	for (i=0; i < I2CSPEED/2; i++) {
+		v;
+	}
+}
+
+/* Set SCL as input and return current level of line, 0 or 1 */
+bool read_SCL(void)
+{
+	PORTB |= SCL; /* set as input */
+	WPUB |= SCL; /* enable pull-up */
+	return (PORTB&SCL);
+}
+
+/* Set SDA as input and return current level of line, 0 or 1 */
+bool read_SDA(void)
+{
+	PORTB |= SDA; /* set as input */
+	WPUB |= SDA; /* enable pull-up */
+	return (PORTB&SDA);
+}
+
+/*  Actively drive SCL signal low */
+void clear_SCL(void)
+{
+	PORTB &= ~SCL; /* set as output */
+	PORTB &= ~SDA; /* set low */
+}
+
+/* Actively drive SDA signal low */
+void clear_SDA(void)
+{
+	PORTB &= ~SCL; /* set as output */
+	PORTB &= ~SDA; /* set low */
+}
+
+void arbitration_lost(void)
+{
+	/* do nothing, since we are the only master */
+}
+ 
+bool started = false; // global data
+void i2c_start_cond(void) {
+  if (started) { // if started, do a restart cond
+    // set SDA to 1
+    read_SDA();
+    I2C_delay();
+    while (read_SCL() == 0) {  // Clock stretching
+      // You should add timeout to this loop
+    }
+    // Repeated start setup time, minimum 4.7us
+    I2C_delay();
+  }
+  if (read_SDA() == 0) {
+    arbitration_lost();
+  }
+  // SCL is high, set SDA from 1 to 0.
+  clear_SDA();
+  I2C_delay();
+  clear_SCL();
+  started = true;
+}
+ 
+void i2c_stop_cond(void){
+  // set SDA to 0
+  clear_SDA();
+  I2C_delay();
+  // Clock stretching
+  while (read_SCL() == 0) {
+    // add timeout to this loop.
+  }
+  // Stop bit setup time, minimum 4us
+  I2C_delay();
+  // SCL is high, set SDA from 0 to 1
+  if (read_SDA() == 0) {
+    arbitration_lost();
+  }
+  I2C_delay();
+  started = false;
+}
+ 
+// Write a bit to I2C bus
+void i2c_write_bit(bool bit) {
+  if (bit) {
+    read_SDA();
+  } else {
+    clear_SDA();
+  }
+  I2C_delay();
+  while (read_SCL() == 0) { // Clock stretching
+    // You should add timeout to this loop
+  }
+  // SCL is high, now data is valid
+  // If SDA is high, check that nobody else is driving SDA
+  if (bit && read_SDA() == 0) {
+    arbitration_lost();
+  }
+  I2C_delay();
+  clear_SCL();
+}
+ 
+// Read a bit from I2C bus
+bool i2c_read_bit(void) {
+  bool bit;
+  // Let the slave drive data
+  read_SDA();
+  I2C_delay();
+  while (read_SCL() == 0) { // Clock stretching
+    // You should add timeout to this loop
+  }
+  // SCL is high, now data is valid
+  bit = read_SDA();
+  I2C_delay();
+  clear_SCL();
+  return bit;
+}
+ 
+// Write a byte to I2C bus. Return 0 if ack by the slave.
+bool i2c_write_byte(bool send_start,
+                    bool send_stop,
+                    unsigned char byte) {
+  unsigned bit;
+  bool nack;
+  if (send_start) {
+    i2c_start_cond();
+  }
+  for (bit = 0; bit < 8; bit++) {
+    i2c_write_bit((byte & 0x80) != 0);
+    byte <<= 1;
+  }
+  nack = i2c_read_bit();
+  if (send_stop) {
+    i2c_stop_cond();
+  }
+  return nack;
+}
+ 
+// Read a byte from I2C bus
+unsigned char i2c_read_byte(bool nack, bool send_stop) {
+  unsigned char byte = 0;
+  unsigned bit;
+  for (bit = 0; bit < 8; bit++) {
+    byte = (byte << 1) | i2c_read_bit();
+  }
+  i2c_write_bit(nack);
+  if (send_stop) {
+    i2c_stop_cond();
+  }
+  return byte;
+}
+

pic/MDR/I2C.h

@@ -0,0 +1,16 @@
+#define __16f1847
+#include <pic16f1847.h>
+#include <stdint.h>
+ 
+#define bool uint8_t
+#define true 1
+#define false 0
+
+#define SCL _RB6 /* pin 12, external 24LC256 I2C EEPROM memory */
+#define SDA _RB7 /* pin 13, external 24LC256 I2C EEPROM memory */
+
+// Write a byte to I2C bus. Return 0 if ack by the slave.
+bool i2c_write_byte(bool send_start, bool send_stop, unsigned char byte);
+ 
+// Read a byte from I2C bus
+unsigned char i2c_read_byte(bool nack, bool send_stop);

pic/MDR/MDR.c

@@ -19,6 +19,7 @@
 #define __16f1847
 #include <pic16f1847.h>
 #include <stdint.h>
+#include "I2C.h"
 
 /* the peripherals connected to the pins */
 #define RELAY1 _RA2 /* pin 1 */
@@ -32,8 +33,8 @@
 /* pin 9 is for a secret function, set by jumper WJ1, Vdd per default */
 /* pin 10 is not connected */
 /* pin 11 in not connected */
-#define MEMORY_CLK _RB6 /* pin 12, external 24LC256 EEPROM */
-#define MEMORY_DATA _RB7 /* pin 13, external 24LC256 EEPROM */
+/* pin 12, external 24LC256 EEPROM */
+/* pin 13, external 24LC256 EEPROM */
 /* pin 14 is Vdd (5V) */
 /* pin 15 is clonnected to external 4MHz ceramic resonator */
 /* pin 16 is clonnected to external 4MHz ceramic resonator */
@@ -72,12 +73,13 @@ uint16_t __at(_CONFIG2) __CONFIG2 = _LVP_ON & /* enable low voltage programming
 /* initialize micro-conroller */
 void init (void) {
 	/* configure IO */
+	NOT_WPUEN = 0; /* enable individual pull-ups */
 	ANSELA = 0; /* all pins are digital */
 	ANSELB = 0; /* all pins are digital */
 	TRISA |= RADIO; /* radio signal is an input */
 	TRISA &= ~(RELAY1|RELAY2); /* relays are outputs */
 	TRISB |= SWITCH1|SWITCH2; /* switches are inputs (with external pull-ups) */
-	TRISB &= ~(LED|MEMORY_CLK|MEMORY_DATA); /* LED is I2C memory are outputs */
+	TRISB &= ~(LED); /* LED is an output (used a sink) */
 	led_off(); /* starting state */
 
 	/* configure switches input */
@@ -109,6 +111,14 @@ void init (void) {
 	TMR2IE = 1; /* enable timer 2 interrupt */
 	TMR2IF = 0; /* clear timer 2 interrupt */
 
+	/* the MDR originally uses a PIC16C54A
+	 * this does does not provide hardware I2C function
+	 * they implement I2C in software (it's even a bit buggy)
+	 * it even does not used open collectors (with pull-ups), but drives the signals
+	 * this PIC16F1847 offers hardware I2C, but not on those pins
+	 * so we also have to use software bit banging I2C
+	 */
+
 	PEIE = 1; /* enable peripheral interrupt (for timer 2) */
 	GIE = 1; /* golablly enable interrupts */
 }