Implement software I2C driver

This driver implements I2C on the EV3 sensor ports for use with NXT and
third-party peripherals.

Author: ArcaneNibble

Makefile

@@ -3,7 +3,7 @@ OBJCOPY = pru-objcopy
 BUILD_TARGET = pru_ledpwm
 
 ASFLAGS += -g
-CFLAGS += -g -Wall -Wno-main -Os
+CFLAGS += -g -Wall -Wimplicit-fallthrough -Wno-main -Os
 LDFLAGS += -g -nostdlib -mmcu=am1808.pru1.specs
 
 .PHONY: all clean

am1808.h

@@ -68,6 +68,12 @@
 // Timer0 peripheral (only what we need)
 static volatile uint32_t * const TIMER0_TIM34 = (volatile uint32_t *)0x01C20014;
 
+// Timer2 peripheral (only what we need)
+static volatile uint32_t * const TIMER2_TIM12 = (volatile uint32_t *)0x01F0C010;
+static volatile uint32_t * const TIMER2_INTCTLSTAT = (volatile uint32_t *)0x01F0C044;
+
+#define TIMER_INTCTLSTAT_PRDINTSTAT12   (1 << 1)
+
 // GPIO peripheral (only what we need)
 typedef struct gpio_bank_t {
     uint32_t dir;