66AK2G12: How to control pin from user space in Linux

Tom Chen

Prodigy 150 points

Part Number: 66AK2G12

Hello,

I have a need to toggle 66AK2G process pins in Linux. I am testing on a EVMK2G board.

I want to control GPIO pins like GPIO0_76.

I configured this pin in Mode3 GPIO pin in the Device Tree in keystone-k2g-evm.dts file:

&k2g_pinctrl {
. . . . . .
   mcasp2_pins: pinmux_mcasp2_pins {

       pinctrl-single,pins = <
           K2G_CORE_IOPAD(0x1234) (BUFFER_CLASS_B | PIN_PULLDOWN | MUX_MODE4)   /* pr0_pru_gpo2.mcasp2_axr2 */
           K2G_CORE_IOPAD(0x1238) (BUFFER_CLASS_B | PIN_PULLDOWN | MUX_MODE4)   /* pr0_pru_gpo3.mcasp2_axr3 */
           K2G_CORE_IOPAD(0x1254) (BUFFER_CLASS_B | PIN_PULLDOWN | MUX_MODE4)   /* pr0_pru_gpo10.mcasp2_afsx */
           K2G_CORE_IOPAD(0x125c) (BUFFER_CLASS_B | PIN_PULLDOWN | MUX_MODE4)   /* pr0_pru_gpo12.mcasp2_aclkx */
       >;
   };

   gpio_pins: pinmux_gpio_pins {
       pinctrl-single,pins = <
            K2G_CORE_IOPAD(0x1130) (PIN_PULLUP   | MUX_MODE3)   /* GPIO0_76 */
        >;
   };

In Linux OS, I tried these commands to configure this pin:

# devmem2 0x02603060 w 0xFFFFEFFF //Set GPIO0_76 Pin direction to output pin

# devmem2 0x02603068 w 0x1000 //Set pin output High in its Set Data Register

# devmem2 0x02603064 //Read output data to confirm this pin output High

0x00001000

However, when I test using multi-meter, this pin output voltage remains Low. is this because I did not set BUFFER_CLASS_x ? I do not know what is BUFFER_CLASS_B, C, D....?

Can someone help me how to correctly configure and toggle 66AK2G pins?

Tom

over 3 years ago

0 Bin Liu over 3 years ago

TI__Guru**** 177101 points

Hi Tom,

Tom Chen said:
   gpio_pins: pinmux_gpio_pins {
       pinctrl-single,pins = <
            K2G_CORE_IOPAD(0x1130) (PIN_PULLUP   | MUX_MODE3)   /* GPIO0_76 */
        >;
   };

This change itself is not sufficient to configure pinmux. This pinmux node has to be referenced somewhere else on another node, this step is necessary to "activate" the pinmux setting. Please check the board DTS file to see how other pinmux nodes are referenced.

After you have done the pinmux properly in board DTS, you can directly use the GPIO pin in kernel sysfs, you don't need to use 'devmem2' to modify any gpio register.

Please see kernel Documentation about gpio in sysfs: Documentation/admin-guide/gpio/sysfs.rst

0 Tom Chen over 3 years ago in reply to Bin Liu

Prodigy 150 points

Bin,

Thank you!

Tom

0 Tom Chen over 3 years ago in reply to Bin Liu

Prodigy 150 points

Bin,

Could you explain BUFFER_CLASS_xx and PULL_xx?

See the website:

elixir.bootlin.com/.../keystone.h

#define BUFFER_CLASS_B	(0 << 19)
#define BUFFER_CLASS_C	(1 << 19)
#define BUFFER_CLASS_D	(2 << 19)
#define BUFFER_CLASS_E	(3 << 19)

#define PULL_DISABLE	(1 << 16)
#define PIN_PULLUP	(1 << 17)
#define PIN_PULLDOWN	(0 << 17)

Tom

0 Bin Liu over 3 years ago in reply to Tom Chen

TI__Guru**** 177101 points

Tom,

Please see the TRM table 5-4 about Pad Configuration Registers.

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66AK2G12: How to control pin from user space in Linux