Goal

Be able to twiddle a gpio line by hand.

Resources

SPRS507F (OMAP3530/25 Applications Processor)

Table 2-1. Ball Characteristics (CBB Pkg.) - Page 28-69 - GPIO pins, mux modes, etc

Caution

If the gpio is already in use by another device in a different mode the results are undefind - and in some cases could cause physical damage to the board (creating a short, for example).

In the kernel via board-overo.c

You might take a glance at Table 2-2. Ball Characteristics (CBC Pkg.) to see which gpio pins are available for use.

If the GPIO you would like to export is pin-muxed, you must enable CONFIG_OMAP_MUX by running menuconfig or editing overo_defconfig

Create a function to export the gpios you need in KERNDIR/arch/arm/mach-omap2/board-overo.c check my other post about custom board files to learn where KERNDIR might be.

#define OVERO_GPIO_CAM_HS 94

static void __init test_custom_gpio_init(void)
{
  printk("... initing test_custom_gpio\n");
  if ((gpio_request(OVERO_GPIO_CAM_HS, "OVERO_GPIO_CAM_HS") == 0) &&
      (gpio_direction_output(OVERO_GPIO_CAM_HS, 1) == 0)) {
    if (0 == gpio_export(OVERO_GPIO_CAM_HS, 0)) {
      printk("exported test_custom_gpio 94");
    } else {
      printk("didn't export test_custom 94");
    }
  } else {
    printk(KERN_ERR "could not obtain test_custom gpio for "
                        "OVERO_GPIO_CAM_HS\n");
  }
}

Then add that function to the list in overo_init

static void __init overo_init(void)
{
  omap3_mux_init(board_mux, OMAP_PACKAGE_CBB);
  overo_i2c_init();
  platform_add_devices(overo_devices, ARRAY_SIZE(overo_devices));
  omap_serial_init();
  overo_flash_init();
  usb_musb_init();
  usb_ehci_init(&ehci_pdata);
  overo_spi_init();
  overo_init_smsc911x();
  overo_display_init();
  test_custom_gpio_init(); // our gpio function

// ... lots more stuff
}

In user-space via `/sys/class/gpio/export`

Note that this cannot be mixed with the in-kernel method method

echo 94 > /sys/class/gpio/export
echo 94 > /sys/class/gpio/unexport

In user-space via `/dev/mem`

TODO

Via uboot

TODO

Updated at 2010-08-03

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