--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/py/touch/touch.c	Fri Dec 21 23:30:16 2012 +0800
@@ -0,0 +1,153 @@
+//
+//  How to access GPIO registers from C-code on the Raspberry-Pi
+//  Example program
+//  15-January-2012
+//  Dom and Gert
+//
+
+
+// Access from ARM Running Linux
+
+#define BCM2708_PERI_BASE        0x20000000
+#define GPIO_BASE                (BCM2708_PERI_BASE + 0x200000) /* GPIO controller */
+
+
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include <dirent.h>
+#include <fcntl.h>
+#include <assert.h>
+#include <sys/mman.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+
+#include <unistd.h>
+
+#define PAGE_SIZE (4*1024)
+#define BLOCK_SIZE (4*1024)
+
+int  mem_fd;
+char *gpio_mem, *gpio_map;
+char *spi0_mem, *spi0_map;
+
+
+// I/O access
+volatile unsigned *gpio;
+
+
+// GPIO setup macros. Always use INP_GPIO(x) before using OUT_GPIO(x) or SET_GPIO_ALT(x,y)
+#define INP_GPIO(g) *(gpio+((g)/10)) &= ~(7<<(((g)%10)*3))
+#define OUT_GPIO(g) *(gpio+((g)/10)) |=  (1<<(((g)%10)*3))
+#define SET_GPIO_ALT(g,a) *(gpio+(((g)/10))) |= (((a)<=3?(a)+4:(a)==4?3:2)<<(((g)%10)*3))
+
+#define FSEL_OFFSET         0   // 0x0000
+#define SET_OFFSET          7   // 0x001c / 4
+#define CLR_OFFSET          10  // 0x0028 / 4
+#define PINLEVEL_OFFSET     13  // 0x0034 / 4
+#define EVENT_DETECT_OFFSET 16  // 0x0040 / 4
+#define RISING_ED_OFFSET    19  // 0x004c / 4
+#define FALLING_ED_OFFSET   22  // 0x0058 / 4
+#define HIGH_DETECT_OFFSET  25  // 0x0064 / 4
+#define LOW_DETECT_OFFSET   28  // 0x0070 / 4
+#define PULLUPDN_OFFSET     37  // 0x0094 / 4
+#define PULLUPDNCLK_OFFSET  38  // 0x0098 / 4
+
+
+#define GPIO_GET(g) ((*(gpio+PINLEVEL_OFFSET)   & (1<<(g))) >> (g))
+#define GPIO_SET(g) (*(gpio+SET_OFFSET) = 1<<(g))  // sets   bits which are 1 ignores bits which are 0
+#define GPIO_CLR(g) (*(gpio+CLR_OFFSET) = 1<<(g))// clears bits which are 1 ignores bits which are 0
+
+#define TOUCH_IN 24
+#define TOUCH_OUT 25
+
+void setup_io();
+
+int main(int argc, char **argv)
+{ 
+  int g,rep;
+
+  // Set up gpi pointer for direct register access
+  setup_io();
+
+  // Switch GPIO 7..11 to output mode
+
+ /************************************************************************\
+  * You are about to change the GPIO settings of your computer.          *
+  * Mess this up and it will stop working!                               *
+  * It might be a good idea to 'sync' before running this program        *
+  * so at least you still have your code changes written to the SD-card! *
+ \************************************************************************/
+
+
+    INP_GPIO(TOUCH_IN);
+    INP_GPIO(TOUCH_OUT);
+    OUT_GPIO(TOUCH_OUT);
+
+    int num = 1000;
+    int sum = 0;
+
+    while (1)
+    {
+int n;
+sum = 0;
+    for (n = 0; n < num; n++)
+{
+            GPIO_CLR(TOUCH_OUT);
+            usleep(1000);
+            GPIO_SET(TOUCH_OUT);
+            while (GPIO_GET(TOUCH_IN) == 0)
+            {
+                sum++;
+            }
+        }
+    printf("total %f\n", (float)sum / num);
+}
+    return 0;
+
+} // main
+
+
+//
+// Set up a memory regions to access GPIO
+//
+void setup_io()
+{
+   /* open /dev/mem */
+   if ((mem_fd = open("/dev/mem", O_RDWR|O_SYNC) ) < 0) {
+      printf("can't open /dev/mem \n");
+      exit (-1);
+   }
+
+   /* mmap GPIO */
+
+   // Allocate MAP block
+   if ((gpio_mem = malloc(BLOCK_SIZE + (PAGE_SIZE-1))) == NULL) {
+      printf("allocation error \n");
+      exit (-1);
+   }
+
+   // Make sure pointer is on 4K boundary
+   if ((unsigned long)gpio_mem % PAGE_SIZE)
+     gpio_mem += PAGE_SIZE - ((unsigned long)gpio_mem % PAGE_SIZE);
+
+   // Now map it
+   gpio_map = (unsigned char *)mmap(
+      (caddr_t)gpio_mem,
+      BLOCK_SIZE,
+      PROT_READ|PROT_WRITE,
+      MAP_SHARED|MAP_FIXED,
+      mem_fd,
+      GPIO_BASE
+   );
+
+   if ((long)gpio_map < 0) {
+      printf("mmap error %d\n", (int)gpio_map);
+      exit (-1);
+   }
+
+   // Always use volatile pointer!
+   gpio = (volatile unsigned *)gpio_map;
+
+
+} // setup_io