Hardware Reference
In-Depth Information
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sysgpio.c : Open/configure /sys GPIO pin
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Here we must open the /sys/class/gpio/gpio17/value and do a
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poll(2) on it, so that we can sense the MCP23017 interrupts.
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8 typedef enum {
9 gp_export = 0, /
/sys/class/gpio/export
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10 gp_unexport, /
/sys/class/gpio/unexport
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11 gp_direction, /
/sys/class/gpo%d/direction
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12 gp_edge, /
/sys/class/gpio%d/edge
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13 gp_value /
/sys/class/gpio%d/value
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14 } gpio_path_t;
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Internal : Create a pathname for type in buf.
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19 static const char
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20 gpio_setpath(int pin,gpio_path_t type,char
buf,unsigned bufsiz) {
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21 static const char
paths[] = {
22 "export", "unexport", "gpio%d/direction",
23 "gpio%d/edge", "gpio%d/value" };
24 int slen;
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26 strncpy(buf,"/sys/class/gpio/",bufsiz);
27 bufsiz -= (slen = strlen(buf));
28 snprintf(buf+slen,bufsiz,paths[type],pin);
29 return buf;
30 }
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32 /
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Open /sys/class/gpio%d/value for edge detection :
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35 static int
36 gpio_open_edge(int pin) {
37 char buf[128];
38 FILE
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f;
39 int fd;
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41 /
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42 gpio_setpath(pin,gp_export,buf,sizeof buf);
43 f = fopen(buf, "w");
44 assert(f);
45 fprintf(f,"%d\n",pin);
46 fclose(f);
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Export pin: /sys/class/gpio/export
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