@@ -5,7 +5,10 @@ import processing.io.*;
 // see setup.png in the sketch folder for wiring details
 
 void setup() {
-  GPIO.pinMode(4, GPIO.INPUT);
+  // INPUT_PULLUP enables the built-in pull-up resistor for this pin
+  // left alone, the pin will read as HIGH
+  // connected to ground (via e.g. a button or switch) it will read LOW
+  GPIO.pinMode(4, GPIO.INPUT_PULLUP);
 }
 
 void draw() {
 
@@ -30,6 +30,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <sys/ioctl.h>
+#include <sys/mman.h>
 #include <sys/param.h>
 #include <time.h>
 #include <unistd.h>
@@ -120,6 +121,143 @@ JNIEXPORT jint JNICALL Java_processing_io_NativeInterface_writeFile
 }
 
 
+JNIEXPORT jint JNICALL Java_processing_io_NativeInterface_raspbianGpioMemRead
+  (JNIEnv *env, jclass cls, jint offset)
+{
+	// validate offset
+	if (4096 <= offset) {
+		return -EINVAL;
+	}
+
+	int file = open("/dev/gpiomem", O_RDWR|O_SYNC);
+	if (file < 0) {
+		return -errno;
+	}
+
+	uint32_t *mem = mmap(NULL, 4096, PROT_READ, MAP_SHARED, file, 0);
+	if (mem == MAP_FAILED) {
+		close(file);
+		return -errno;
+	}
+
+	uint32_t value = mem[offset];
+
+	munmap(mem, 4096);
+	close(file);
+	return value;
+}
+
+
+JNIEXPORT jint JNICALL Java_processing_io_NativeInterface_raspbianGpioMemWrite
+  (JNIEnv *env, jclass cls, jint offset, jint mask, jint value)
+{
+	// validate offset
+	if (4096 <= offset) {
+		return -EINVAL;
+	}
+
+	int file = open("/dev/gpiomem", O_RDWR|O_SYNC);
+	if (file < 0) {
+		return -errno;
+	}
+
+	uint32_t *mem = mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_SHARED, file, 0);
+	if (mem == MAP_FAILED) {
+		close(file);
+		return -errno;
+	}
+
+	mem[offset] = (mem[offset] & ~mask) | (value & mask);
+
+	munmap(mem, 4096);
+	close(file);
+	return 1;	// number of bytes written
+}
+
+
+#define BCM2835_GPPUD_OFFSET (0x94 >> 2)
+#define BCM2835_GPPUDCLK0_OFFSET (0x98 >> 2)
+#define BCM2835_GPPUDCLK1_OFFSET (0x9c >> 2)
+
+JNIEXPORT jint JNICALL Java_processing_io_NativeInterface_raspbianGpioMemSetPinBias
+  (JNIEnv *env, jclass cls, jint gpio, jint mode)
+{
+	int ret = 0;	// success
+
+	int file = open("/dev/gpiomem", O_RDWR|O_SYNC);
+	if (file < 0) {
+		return -errno;
+	}
+
+	uint32_t *mem = mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_SHARED, file, 0);
+	if (mem == MAP_FAILED) {
+		close(file);
+		return -errno;
+	}
+
+	// validate arguments
+	if (gpio < 0 || 53 < gpio) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	// see BCM2835 datasheet, p. 101
+	uint32_t pud;
+	if (mode == 0) {
+		pud = 0;	// floating
+	} else if (mode == 2) {
+		pud = 2;	// pull-up
+	} else if (mode == 3) {
+		pud = 1;	// pull-down
+	} else {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	/*
+	 * From the BCM2835 datasheet, p. 101:
+	 *
+	 * The following sequence of events is required:
+	 * 1. Write to GPPUD to set the required control signal (i.e. Pull-up or
+	 *    Pull-Down or neither to remove the current Pull-up/down)
+	 * 2. Wait 150 cycles – this provides the required set-up time for the
+	 *    control signal
+	 * 3. Write to GPPUDCLK0/1 to clock the control signal into the GPIO pads
+	 *    you wish to modify – NOTE only the pads which receive a clock will
+	 *    be modified, all others will retain their previous state.
+	 * 4. Wait 150 cycles – this provides the required hold time for the
+	 *    control signal
+	 * 5. Write to GPPUD to remove the control signal
+	 * 6. Write to GPPUDCLK0/1 to remove the clock
+	 */
+
+	// python-gpiozero uses a delay of 214 ns, so we do the same
+	struct timespec wait;
+	wait.tv_sec = 0;
+	wait.tv_nsec = 214;
+
+	mem[BCM2835_GPPUD_OFFSET] = pud;
+	nanosleep(&wait, NULL);
+	if (gpio < 32) {
+		mem[BCM2835_GPPUDCLK0_OFFSET] = 1 << gpio;
+	} else {
+		mem[BCM2835_GPPUDCLK1_OFFSET] = 1 << (gpio-32);
+	}
+	nanosleep(&wait, NULL);
+	mem[BCM2835_GPPUD_OFFSET] = 0;
+	if (gpio < 32) {
+		mem[BCM2835_GPPUDCLK0_OFFSET] = 0;
+	} else {
+		mem[BCM2835_GPPUDCLK1_OFFSET] = 0;
+	}
+
+out:
+	munmap(mem, 4096);
+	close(file);
+	return ret;
+}
+
+
 JNIEXPORT jint JNICALL Java_processing_io_NativeInterface_pollDevice
   (JNIEnv *env, jclass cls, jstring _fn, jint timeout)
 {
 
@@ -328,7 +328,7 @@ public static void noInterrupts() {
   /**
    *  Configures a pin to act either as input or output
    *  @param pin GPIO pin
-   *  @param mode GPIO.INPUT or GPIO.OUTPUT
+   *  @param mode GPIO.INPUT, GPIO.INPUT_PULLUP, GPIO.INPUT_PULLDOWN, or GPIO.OUTPUT
    *  @see digitalRead
    *  @see digitalWrite
    *  @see releasePin
@@ -369,16 +369,29 @@ public static void pinMode(int pin, int mode) {
     String out;
     if (mode == INPUT) {
       out = "in";
+
+      // attempt to disable any pre-set pullups on the Raspberry Pi
+      NativeInterface.raspbianGpioMemSetPinBias(pin, mode);
+
     } else if (mode == OUTPUT) {
       if (values.get(pin)) {
         out = "high";
       } else {
         out = "low";
       }
     } else if (mode == INPUT_PULLUP || mode == INPUT_PULLDOWN) {
+      out = "in";
+
+      // attempt to set pullups on the Raspberry Pi
+      ret = NativeInterface.raspbianGpioMemSetPinBias(pin, mode);
+      if (ret == -2) {    // NOENT
+        System.err.println("Setting pullup or pulldown resistors is currently only supported on the Raspberry Pi running Raspbian. Continuing without.");
+      } else if (ret < 0) {
+        System.err.println("Error setting pullup or pulldown resistors: " + NativeInterface.getError(ret) + ". Continuing without.");
+      }
       // currently this can't be done in a non-platform-specific way, see
       // http://lists.infradead.org/pipermail/linux-rpi-kernel/2015-August/002146.html
-      throw new RuntimeException("Not yet implemented");
+
     } else {
       throw new IllegalArgumentException("Unknown mode");
     }
 
@@ -62,6 +62,9 @@ public static int writeFile(String fn, String out) {
   }
 
   /* GPIO */
+  public static native int raspbianGpioMemRead(int offset);
+  public static native int raspbianGpioMemWrite(int offset, int mask, int value);
+  public static native int raspbianGpioMemSetPinBias(int gpio, int mode);
   public static native int pollDevice(String fn, int timeout);
   /* I2C */
   public static native int transferI2c(int handle, int slave, byte[] out, byte[] in);
Original file line number	Diff line number	Diff line change
@@ -62,6 +62,9 @@ public static int writeFile(String fn, String out) {
62	62	}
63	63
64	64	/* GPIO */
	65	+ public static native int raspbianGpioMemRead(int offset);
	66	+ public static native int raspbianGpioMemWrite(int offset, int mask, int value);
	67	+ public static native int raspbianGpioMemSetPinBias(int gpio, int mode);
65	68	public static native int pollDevice(String fn, int timeout);
66	69	/* I2C */
67	70	public static native int transferI2c(int handle, int slave, byte[] out, byte[] in);