test I2C: fails. same code produce similar result every 9 times

pic/MDR/I2C.c

@@ -1,47 +1,44 @@
 /* software bit banging implementation
  * based on https://en.wikipedia.org/wiki/I2c example code
+ *
+ * there is no external pull-up on SCL, and the internal one is too weak
+ * SCL must be driven
+ * but that is ok as we are the only master
+ * there is an external pull-up on SDA, and the internal one is too weak
+ * SDA goes to 3V instead of 5V due to the external pull-up
+ * but the 24LC256 still seems to work
  */
 #include "I2C.h"
 
 // Hardware-specific support functions that MUST be customized:
-#define I2CSPEED 100
+/* even when doing nothing, the max speed will be 100kHz, while the chip supports 400kHz */
-void I2C_delay()
+#define 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 */
+	LATB |= SCL; /* set high (must be driven because no pull-up */
-	WPUB |= SCL; /* enable pull-up */
+	return 1;
-	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 */
+	TRISB |= SDA; /* set as input */
-	WPUB |= SDA; /* enable pull-up */
+	return (PORTB&SDA)!=0;
-	return (PORTB&SDA);
 }
 
 /*  Actively drive SCL signal low */
 void clear_SCL(void)
 {
-	PORTB &= ~SCL; /* set as output */
+	LATB &= ~SCL; /* set low */
-	PORTB &= ~SDA; /* set low */
 }
 
 /* Actively drive SDA signal low */
 void clear_SDA(void)
 {
-	PORTB &= ~SCL; /* set as output */
+	TRISB &= ~SDA; /* set as output */
-	PORTB &= ~SDA; /* set low */
+	LATB &= ~SDA; /* set low */
 }
 
 void arbitration_lost(void)
@@ -111,51 +108,52 @@ void i2c_write_bit(bool bit) {
  
 // Read a bit from I2C bus
 bool i2c_read_bit(void) {
-  bool bit;
+	bool bit;
-  // Let the slave drive data
+	// Let the slave drive data
-  read_SDA();
+	read_SDA();
-  I2C_delay();
+	I2C_delay();
-  while (read_SCL() == 0) { // Clock stretching
+	while (read_SCL() == 0) { // Clock stretching
-    // You should add timeout to this loop
+
-  }
+	// You should add timeout to this loop
-  // SCL is high, now data is valid
+	}
-  bit = read_SDA();
+	// SCL is high, now data is valid
-  I2C_delay();
+	bit = read_SDA();
-  clear_SCL();
+	I2C_delay();
-  return bit;
+	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 i2c_write_byte(bool send_start, bool send_stop, unsigned char byte)
-                    bool send_stop,
+{
-                    unsigned char byte) {
+	unsigned bit;
-  unsigned bit;
+	bool nack;
-  bool nack;
+	if (send_start) {
-  if (send_start) {
+		i2c_start_cond();
-    i2c_start_cond();
+	}
-  }
+	for (bit = 0; bit < 8; bit++) {
-  for (bit = 0; bit < 8; bit++) {
+		i2c_write_bit((byte & 0x80) != 0);
-    i2c_write_bit((byte & 0x80) != 0);
+		byte <<= 1;
-    byte <<= 1;
+	}
-  }
+	nack = i2c_read_bit();
-  nack = i2c_read_bit();
+	if (send_stop) {
-  if (send_stop) {
+		i2c_stop_cond();
-    i2c_stop_cond();
+	}
-  }
+	return nack;
-  return nack;
 }
  
 // Read a byte from I2C bus
-unsigned char i2c_read_byte(bool nack, bool send_stop) {
+unsigned char i2c_read_byte(bool nack, bool send_stop)
-  unsigned char byte = 0;
+{
-  unsigned bit;
+	unsigned char byte = 0;
-  for (bit = 0; bit < 8; bit++) {
+	unsigned bit;
-    byte = (byte << 1) | i2c_read_bit();
+	for (bit = 0; bit < 8; bit++) {
-  }
+		byte = (byte << 1) | i2c_read_bit();
-  i2c_write_bit(nack);
+	}
-  if (send_stop) {
+	i2c_write_bit(nack);
-    i2c_stop_cond();
+	if (send_stop) {
-  }
+		i2c_stop_cond();
-  return byte;
+	}
+	return byte;
 }
 

pic/MDR/MDR.c

@@ -42,8 +42,8 @@
 /* pin 18 is for a secret function, set by jumper WJ2, Vdd per default */
 
 /* simple functions */
-#define led_off() PORTB |= LED
+#define led_off() LATB |= LED
-#define led_on() PORTB &= ~(LED)
+#define led_on() LATB &= ~(LED)
 #define sleep() __asm sleep __endasm
 
 /* variables */
@@ -69,11 +69,9 @@ uint16_t __at(_CONFIG2) __CONFIG2 = _LVP_ON & /* enable low voltage programming
                                     _PLLEN_OFF & /* don't use 4X PLL, for longer timer */
                                     _WRT_OFF; /* no flash write protect */
 
-
 /* 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 */
@@ -118,6 +116,8 @@ void init (void) {
 	 * this PIC16F1847 offers hardware I2C, but not on those pins
 	 * so we also have to use software bit banging I2C
 	 */
+	TRISB &= ~SCL; /* set as output (it must be driven because there is no pull-up */
+	LATB |= SCL; /* set clock as high (default pull-up state) */ 
 
 	PEIE = 1; /* enable peripheral interrupt (for timer 2) */
 	GIE = 1; /* golablly enable interrupts */
@@ -161,6 +161,11 @@ static void interrupt(void) __interrupt 0
 			if (switches&SWITCH1) { /* switch 1 changed */
 				if (PORTB&SWITCH1) { /* switch 1 released */
 					led_off(); /* reset LED */
+					i2c_write_byte(1,0,0xa0);
+					i2c_write_byte(0,1,0xa0);
+//					i2c_write_byte(0,1,0x17);
+//					i2c_write_byte(1,0,0xa1);
+//					i2c_read_byte(0,0);
 				} else { /* switch 1 pressed */
 					led_on(); /* test LED */
 				}

pic/MDR/Makefile

@@ -15,9 +15,9 @@ OBJ := $(patsubst %.c,%.o,$(SRC))
 
 all: compile flash
 
-# flash program
+# flash program (the board needs to power externally)
 flash: $(TARGET).hex
-	pk2cmd -PPIC$(PIC) -F$< -M -W -R
+	pk2cmd -P PIC$(PIC) -F $< -M -W -R
 
 # compile stages
 assembly: $(ASM)
@@ -36,7 +36,7 @@ compile: hex
 	gpasm -I . -o $@ -c $<
 
 $(TARGET).hex: $(OBJ)
-	gplink -w -r -s /usr/share/gputils/lkr/$(PIC)_g.lkr -I/usr/share/sdcc/lib/pic14 -I/usr/share/sdcc/non-free/lib/pic14 -I. -o $@ libsdcce.lib pic$(PIC).lib $<
+	gplink -w -r -s /usr/share/gputils/lkr/$(PIC)_g.lkr -I /usr/share/sdcc/lib/pic14 -I /usr/share/sdcc/non-free/lib/pic14 -I . -o $@ libsdcce.lib pic$(PIC).lib $(OBJ)
 
 # remove temporary files
 clean: