// gpio.c #include<stdio.h> #include<stdlib.h> #include<fcntl.h> #include<unistd.h> // The specific GPIO being used must be setup and replaced thru // this code. The GPIO of 240 is in the path of most the sys dirs // and in the export write. // // Figuring out the exact GPIO was not totally obvious when there // were multiple GPIOs in the system. One way to do is to go into // the gpiochips in /sys/class/gpio and view the label as it should // reflect the address of the GPIO in the system. The name of the // the chip appears to be the 1st GPIO of the controller. // // The export causes the gpio240 dir to appear in /sys/class/gpio. // Then the direction and value can be changed by writing to them. // The performance of this is pretty good, using a nfs mount, // running on open source linux, on the ML507 reference system, // the GPIO can be toggled about every 4 usec. // The following commands from the console setup the GPIO to be // exported, set the direction of it to an output and write a 1 // to the GPIO. // // bash> echo 900 > /sys/class/gpio/export // bash> echo out > /sys/class/gpio/gpio900/direction // bash> echo 1 > /sys/class/gpio/gpio900/value // if sysfs is not mounted on your system, the you need to mount it // bash> mount -t sysfs sysfs /sys // the following bash script to toggle the gpio is also handy for // testing // // while [ 1 ]; do // echo 1 > /sys/class/gpio/gpio900/value // sleep 1 // echo 0 > /sys/class/gpio/gpio900/value // sleep 1 // done // to compile this, use the following command // gcc gpio.c -o gpio // The kernel needs the following configuration to make this work. // // CONFIG_GPIO_SYSFS=y // CONFIG_SYSFS=y // CONFIG_EXPERIMENTAL=y // CONFIG_GPIO_XILINX=y intmain() { int valuefd, exportfd, directionfd; printf("GPIO test running...\n"); // The GPIO has to be exported to be able to see it // in sysfs exportfd = open("/sys/class/gpio/export", O_WRONLY); if (exportfd < 0) { printf("Cannot open GPIO to export it\n"); exit(1); } write(exportfd, "900", 4); close(exportfd); printf("GPIO exported successfully\n"); // Update the direction of the GPIO to be an output directionfd = open("/sys/class/gpio/gpio900/direction", O_RDWR); if (directionfd < 0) { printf("Cannot open GPIO direction it\n"); exit(1); } write(directionfd, "out", 4); close(directionfd); printf("GPIO direction set as output successfully\n"); // Get the GPIO value ready to be toggled valuefd = open("/sys/class/gpio/gpio900/value", O_RDWR); if (valuefd < 0) { printf("Cannot open GPIO value\n"); exit(1); } printf("GPIO value opened, now toggling...\n"); // toggle the GPIO as fast a possible forever, a control c is needed // to stop it while (1) { write(valuefd,"1", 2); sleep(1); write(valuefd,"0", 2); sleep(1); } }
