Using a GPIO in Linux

1 Using a GPIO from Command Line
- 1.1 Configure GPIO as Input
- 1.2 Read GPIO level
- 1.3 Configure GPIO as Output
- 1.4 Write GPIO level
2 Trizeps VII & Trizeps VIII GPIOs

Almost all function pins of a SOC are GPIO ( General Purpose Input Output).
They can be configured to serve as a simple input, output or with a special function (i.e. I2C or UART).
Most pins can be configured with additional settings like drive-strength, pull-up or -down, keeper, etc.

Using a GPIO from Command Line

As already mentioned a pin can be configured to serve as GPIO or as a special function.
The following commands only work as expected, when the pin is configured as GPIO!

Path in Sysfs:

/sys/class/gpio

First thing to do, is to export control of a GPIO to userspace by writing its number to 'export':

$ echo 68 > /sys/class/gpio/export

This will create an entry for gpio3.IO[4] = ((bank-1)*32)+pin = ((3-1)*32)+4 = 68 at:

/sys/class/gpio/gpio68

To reverse the effect of exporting GPIO 68 to userspace call:

$ echo 68 > /sys/class/gpio/unexport

Configure GPIO as Input

$ echo in > /sys/class/gpio/gpio68/direction

Read GPIO level

$ cat /sys/class/gpio/gpio68/value

Configure GPIO as Output

$ echo out > /sys/class/gpio/gpio68/direction

Instead of using 'out', you can use 'low' and 'high' to ensure glitch free initialization:

$ echo high > /sys/class/gpio/gpio68/direction

$ echo low > /sys/class/gpio/gpio68/direction

Write GPIO level

Set pin low:

$ echo 0 > /sys/class/gpio/gpio68/value

Set pin high:

$ echo 1 > /sys/class/gpio/gpio68/value

Trizeps VII & Trizeps VIII GPIOs

SODIMM	Name	Trizeps VII	Trizeps VIII, Trizeps VIII Mini

SODIMM	Name	Trizeps VII	Trizeps VIII, Trizeps VIII Mini
1	MIC_OUT
2	AD3
3	MIC_GND
4	AD2
5	LINEIN_L
6	AD1
7	LINEIN_R
8	AD0
9	AGND
10	VDDA
11	AGND
12	VDDA
13	HEADPHONE_GND
14	TSPX
15	HEADPHONE_L
16	TSMX
17	HEADPHONE_R
18	TSPY
19	UART3_RXD	gpio4.IO[7]	gpio5.IO[6]
20	TSMY
21	UART3_TXD	gpio4.IO[6]	gpio5.IO[7]
22	VDD_OTP		gpio5.IO[8]
23	UART1_DTR	gpio7.IO[7]	gpio3.IO[19]
24	BATT		gpio5.IO[9]
25	UART1_CTS	gpio7.IO[3]	gpio5.IO[27]
26	RESET_IN	gpio2.IO[7]
27	UART1_RTS	gpio7.IO[2]	gpio5.IO[26]
28	SPEAKER_P
29	UART1_DSR	gpio6.IO[14]	gpio3.IO[20]
30	SPEAKER_L
31	UART1_DCD	gpio6.IO[15]	gpio4.IO[21]
32	UART2_CTS	gpio7.IO[5]	gpio5.IO[29]
33	UART1_RXD	gpio7.IO[1]	gpio5.IO[22]
34	UART2_RTS	gpio7.IO[4]	gpio5.IO[28]
35	UART1_TXD	gpio7.IO[0]	gpio5.IO[23]
36	UART2_RXD	gpio6.IO[18]	gpio5.IO[24]
37	UART1_RI	gpio1.IO[5]	gpio4.IO[22]
38	UART2_TXD	gpio6.IO[17]	gpio5.IO[25]
39	GND
40	VCC
41	GND
42	VCC
43	IRQ_SP43	gpio2.IO[6]	gpio1.IO[7]
44	LCD_DE	gpio4.IO[17]
45	SP45	gpio2.IO[3]	gpio3.IO[4]
46	LCD_D07	gpio4.IO[28]
47	SD2_CLK	gpio1.IO[10]	gpio2.IO[13]
48	LCD_D09	gpio4.IO[30]
49	CIF_DATA0	gpio5.IO[30]	gpio4.IO[2]
50	LCD_D11	gpio5.IO[5]
51	SD2_DATA3	gpio1.IO[12]	gpio2.IO[18]
52	LCD_D12	gpio5.IO[6]
53	CIF_DATA1	gpio5.IO[31]	gpio4.IO[3]
54	LCD_D13	gpio5.IO[7]
55	SP55	gpio2.IO[5]	gpio3.IO[21]
56	LCD_PCLK	gpio4.IO[16]
57	CIF_DATA2	gpio6.IO[0]	gpio4.IO[4]
58	LCD_D03	gpio4.IO[24]
59	SD2_CARD_DETECT	gpio1.IO[4]	gpio2.IO[12]
60	LCD_D02	gpio4.IO[23]
61	CIF_DATA3	gpio6.IO[1]	gpio4.IO[5]
62	LCD_D08	gpio4.IO[29]
63	CIF_DATA4	gpio6.IO[2]	gpio4.IO[6]
64	LCD_D15	gpio5.IO[9]
65	CIF_DATA5	gpio6.IO[3]	gpio4.IO[7]
66	LCD_D14	gpio5.IO[8]
67	CIF_DATA6	gpio6.IO[4]	gpio4.IO[8]
68	LCD_HSYNC	gpio4.IO[18]
69	PWM1	gpio6.IO[9]	gpio5.IO[2]
70	LCD_D01	gpio4.IO[22]
71	CIF_DATA7	gpio6.IO[5]	gpio4.IO[9]
72	LCD_D05	gpio4.IO[26]
73	CIF_DATA8 / Backlight_Enable	gpio4.IO[20]	gpio3.IO[22]
74	LCD_D10	gpio4.IO[31]
75	CIF_DATA9 / SP75	gpio5.IO[28]	gpio3.IO[23]
76	LCD_D00	gpio4.IO[21]
77	PWM2