add PCA9685 driver

pca9685/registers.go

@@ -0,0 +1,69 @@
+package pca9685
+
+// Software reset addresses for generic i2c implementation
+// and PCA specific SWRST. See section 7.6
+const (
+	I2CSWRSTADR      = 0x0
+	PCA9685SWRSTBYTE = 0b0000_0110 // 0x06
+)
+
+// Registries with nomenclature as seen in manual
+const (
+	SUBADR1 uint8 = 0x2
+	SUBADR2 uint8 = 0x3
+	SUBADR3 uint8 = 0x4
+
+	MODE1      uint8 = 0x0
+	MODE2      uint8 = 0x1
+	ALLCALLADR uint8 = 0x05
+
+	SWRESET uint8 = 0b0000_0011
+
+	// Start of LED registries. corresponds to LED0_ON_L register.
+	// Use LED function to get registries of a specific PWM channel register.
+	LEDSTART = 0x06
+)
+
+// MODE1
+const (
+	RESET             byte = 0b1000_0000
+	EXTCLK            byte = 0b0100_0000
+	AI                byte = 0b0010_0000
+	SLEEP             byte = 0b0001_0000
+	defaultMODE1Value byte = 0b0001_0001
+)
+
+// MODE2
+const (
+	OUTDRV = 1 << 2
+	INVRT  = 1 << 4
+)
+
+// LED channels from 0-15. Returns 4 registries associated with
+// the channel PWM signal. Channel 250 (0xFA) gives ALL_LED registers.
+// The L suffix represents the 8 LSB of 12 bit timing, the H suffix represents
+// the 4 MSB of the timing. This way you have 0-4095 timing options. ON or OFF
+// will be a number between these two or will be simply ON or OFF (fifth bit of H registry).
+//
+// The SetPWM implementation in this library does not do phase-shifting so OFF will always
+// happen at time stamp 0. ON will solely decide duty cycle.
+func LED(ch uint8) (ONL, ONH, OFFL, OFFH uint8) {
+	switch {
+	case ch == ALLLED:
+		return ALLLED, ALLLED + 1, ALLLED + 2, ALLLED + 3
+
+	case ch > 15:
+		panic("PWM channel out of range [0-15]")
+	default:
+	}
+	// 4 registries per channel. Starts at 6
+	onLReg := LEDSTART + 4*ch
+	return onLReg, onLReg + 1, onLReg + 2, onLReg + 3
+}
+
+const (
+	// ALLLED is channel that selects registries to control all leds. Use with function LED
+	ALLLED = 0xfa
+	// PRESCALE Prescaling byte
+	PRESCALE byte = 0xFE
+)