embarassingly, this is not getting picked up.  try one more time.

so we have gpio

Reference: /n/atom/patch/applied/pigpio
Date: Sun Jan 10 20:03:43 CET 2016
Signed-off-by: quanstro@quanstro.net

--- /sys/src/9/bcm/gpio.c	Thu Jan  1 00:00:00 1970
+++ /sys/src/9/bcm/gpio.c	Sun Jan 10 20:03:33 2016
@@ -0,0 +1,95 @@
+/*
+ * Raspberry Pi GPIO support
+ */
+
+#include "u.h"
+#include "../port/lib.h"
+#include "../port/error.h"
+#include "mem.h"
+#include "dat.h"
+#include "fns.h"
+#include "io.h"
+
+#define GPIOREGS	(VIRTIO+0x200000)
+
+/* GPIO regs */
+enum {
+	Fsel0	= 0x00>>2,
+		FuncMask= 0x7,
+	Set0	= 0x1c>>2,
+	Clr0	= 0x28>>2,
+	Lev0	= 0x34>>2,
+	PUD	= 0x94>>2,
+		Off	= 0x0,
+		Pulldown= 0x1,
+		Pullup	= 0x2,
+	PUDclk0	= 0x98>>2,
+	PUDclk1	= 0x9c>>2,
+};
+
+void
+gpiosel(uint pin, int func)
+{	
+	u32int *gp, *fsel;
+	int off;
+
+	gp = (u32int*)GPIOREGS;
+	fsel = &gp[Fsel0 + pin/10];
+	off = (pin % 10) * 3;
+	*fsel = (*fsel & ~(FuncMask<<off)) | func<<off;
+}
+
+static void
+gpiopull(uint pin, int func)
+{
+	u32int *gp, *reg;
+	u32int mask;
+
+	gp = (u32int*)GPIOREGS;
+	reg = &gp[PUDclk0 + pin/32];
+	mask = 1 << (pin % 32);
+	gp[PUD] = func;
+	microdelay(1);
+	*reg = mask;
+	microdelay(1);
+	*reg = 0;
+}
+
+void
+gpiopulloff(uint pin)
+{
+	gpiopull(pin, Off);
+}
+
+void
+gpiopullup(uint pin)
+{
+	gpiopull(pin, Pullup);
+}
+
+void
+gpiopulldown(uint pin)
+{
+	gpiopull(pin, Pulldown);
+}
+
+void
+gpioout(uint pin, int set)
+{
+	u32int *gp;
+	int v;
+
+	gp = (u32int*)GPIOREGS;
+	v = set? Set0 : Clr0;
+	gp[v + pin/32] = 1 << (pin % 32);
+}
+
+int
+gpioin(uint pin)
+{
+	u32int *gp;
+
+	gp = (u32int*)GPIOREGS;
+	return (gp[Lev0 + pin/32] & (1 << (pin % 32))) != 0;
+}
+