Updated Pull-up/Pull-down to support BCM2711 and PRi4

go.mod

@@ -1 +1,3 @@
 module github.com/stianeikeland/go-rpio/v4
+
+go 1.13

rpio.go

@@ -63,6 +63,8 @@ See the spec for full details of the BCM2835 controller:
 https://www.raspberrypi.org/documentation/hardware/raspberrypi/bcm2835/BCM2835-ARM-Peripherals.pdf
 and https://elinux.org/BCM2835_datasheet_errata - for errors in that spec
 
+Changes to support the BCM2711, used on the Raspberry Pi 4, were cribbed from https://github.com/RPi-Distro/raspi-gpio/
+
 */
 package rpio
 
@@ -96,6 +98,14 @@ const (
 	memLength = 4096
 )
 
+// BCM 2711 has a differnet mechanism for pin pull-up/pull-down/enable
+const (
+	GPPUPPDN0 = 57        // Pin pull-up/down for pins 15:0 
+	GPPUPPDN1 = 58        // Pin pull-up/down for pins 31:16 
+	GPPUPPDN2 = 59        // Pin pull-up/down for pins 47:32 
+	GPPUPPDN3 = 60        // Pin pull-up/down for pins 57:48
+)
+
 var (
 	gpioBase int64
 	clkBase  int64
@@ -240,6 +250,25 @@ func (pin Pin) PullOff() {
 	PullMode(pin, PullOff)
 }
 
+func (pin Pin) ReadPull() Pull {
+	if !isBCM2711() {
+		return PullOff	// TODO: Can you read pull state on other Pi boards?
+	}
+
+	reg := GPPUPPDN0 + (uint8(pin) >> 4)
+	bits := gpioMem[reg] >> ((uint8(pin) & 0xf) << 1) & 0x3
+	switch bits {
+	case 0:
+		return PullOff
+	case 1:
+		return PullUp
+	case 2:
+		return PullDown
+	default:
+		return PullOff
+	}
+}
+
 // Detect: Enable edge event detection on pin
 func (pin Pin) Detect(edge Edge) {
 	DetectEdge(pin, edge)
@@ -430,14 +459,36 @@ func EdgeDetected(pin Pin) bool {
 }
 
 func PullMode(pin Pin, pull Pull) {
+		
+	memlock.Lock()
+	defer memlock.Unlock()
+
+	if isBCM2711() {
+		pullreg := GPPUPPDN0 + (pin >> 4)
+		pullshift := (pin & 0xf) << 1
+		
+		var p uint32 
+		
+		switch pull {
+		case PullOff:
+			p = 0
+		case PullUp:
+			p = 1
+		case PullDown:
+			p = 2;
+		}
+		
+		// This is verbatim C code from raspi-gpio.c
+		pullbits := gpioMem[pullreg]
+		pullbits &= ^(3 << pullshift)
+		pullbits |= (p << pullshift)
+		gpioMem[pullreg]= pullbits
+	} else {
 		// Pull up/down/off register has offset 38 / 39, pull is 37
 		pullClkReg := pin/32 + 38
 		pullReg := 37
 		shift := pin % 32
 		
-	memlock.Lock()
-	defer memlock.Unlock()
-
 		switch pull {
 		case PullDown, PullUp:
 			gpioMem[pullReg] |= uint32(pull)
@@ -455,7 +506,7 @@ func PullMode(pin Pin, pull Pull) {
 		
 		gpioMem[pullReg] &^= 3
 		gpioMem[pullClkReg] = 0
-
+	}
 }
 
 // SetFreq: Set clock speed for given pin in Clock or Pwm mode
@@ -755,3 +806,9 @@ func getBase() int64 {
 	// Default to Pi 1
 	return int64(bcm2835Base)
 }
+
+// The Pi 4 uses a BCM 2711, which has different register offsets and base addresses than the rest of the Pi family (so far).  This
+// helper function checks if we're on a 2711 and hence a Pi 4
+func isBCM2711() bool {
+	return gpioMem[GPPUPPDN3] != 0x6770696f
+}