Using a GPIO in Linux

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/gpioThe first

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
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	gpio1.IO[9]	gpio1.IO[1]
78	LCD_D04	gpio4.IO[25]
79	POWERFAIL	gpio2.IO[4]	gpio3.IO[24]
80	LCD_D06	gpio4.IO[27]
81	SD2_DATA1	gpio1.IO[14]	gpio2.IO[16]
82	LCD_VSYNC	gpio4.IO[19]
83	GND
84	VCC
85	SD2_DATA2	gpio1.IO[13]	gpio2.IO[17]
86	CIF_VSYNC / SPI_SS0	gpio4.IO[9] / gpio5.IO[21]	gpio5.IO[13]
87	RESET_OUT	gpio7.IO[12]	gpio1.IO[2] / gpio3.IO[14]
88	CIF_MCLK / SPI_SCLK	gpio4.IO[6] / gpio1.IO[0]	gpio4.IO[20] / gpio5.IO[10]
89	WE / SP89	gpio2.IO[26]
90	CIF_PCLK	gpio4.IO[8] / gpio5.IO[18]	gpio4.IO[1] / gpio5.IO[12]
91	OE / SP91	gpio2.IO[25]
92	CIF_HSYNC	gpio4.IO[8] / gpio5.IO[19]	gpio4.IO[0] / gpio5.IO[11]
93	RD/WR / SP95	gpio5.IO[29]	gpio3.IO[18]
94	I2C1_SCL / SP94	gpio5.IO[27]	gpio5.IO[14]
95	RDY	gpio5.IO[0]	gpio3.IO[16]
96	I2C1_SDA / SP96	gpio5.IO[26]	gpio5.IO[15]
97	CAN1_RX	gpio1.IO[8]
98	SP98	gpio7.IO[6]	gpio1.IO[0]
99	CAN1_TX	gpio1.IO[7]
100	LCD_PWR_EN	gpio5.IO[20]	gpio1.IO[5]
101	CAN2_RX	gpio4.IO[15]	gpio4.IO[31]
102	SP102	gpio7.IO[8]	gpio1.IO[8]
103	CAN2_TX	gpio4.IO[14]	gpio5.IO[0]
104	SP104	gpio2.IO[27]	gpio3.IO[11]
105	CS1		gpio3.IO[0]
106	CS4		gpio3.IO[25]
107	CS3	gpio2.IO[23]	gpio3.IO[1]
108	VCC
109	GND
110	A08	gpio3.IO[8]	gpio4.IO[12]
111	A00	gpio3.IO[0]	gpio3.IO[6]
112	A09	gpio3.IO[9]	gpio4.IO[13]
113	A01	gpio3.IO[1]	gpio3.IO[7]
114	A10	gpio3.IO[10]	gpio4.IO[14]
115	A02	gpio3.IO[2]	gpio5.IO[20]
116	A11	gpio3.IO[11]	gpio4.IO[15]
117	A03	gpio3.IO[3]	gpio3.IO[8]
118	A12	gpio3.IO[12]	gpio4.IO[16]
119	A04	gpio3.IO[4]	gpio3.IO[9]
120	A13	gpio3.IO[13]	gpio4.IO[17]
121	A05	gpio3.IO[5]	gpio3.IO[10]
122	A14	gpio3.IO[14]	gpio4.IO[18]
123	A06	gpio3.IO[6]	gpio1.IO[3]
124	A15	gpio3.IO[15]	gpio4.IO[19]
125	A07	gpio3.IO[7]	gpio1.IO[6]
126	DQM0	gpio2.IO[28]	gpio4.IO[10]
127	USB_OTG_PEN	gpio2.IO[0]	gpio1.IO[12]
128	DQM1	gpio2.IO[29]	gpio4.IO[11]
129	USB_HOST_PEN	gpio2.IO[2]	gpio1.IO[14]
130	DQM2	gpio2.IO[30]
131	USB_HOST_OC	gpio1.IO[3]	gpio1.IO[15]
132	DQM3	gpio2.IO[31]	gpio3.IO[12]
133	USB_OTG_OC	gpio6.IO[10]	gpio1.IO[13]
134	A25	gpio5.IO[2]	gpio3.IO[3]
135	USB_OTG_VBUS
136	A24	gpio5.IO[4]	gpio3.IO[15]
137	USB_OTG_ID	gpio1.IO[1]
138	A23	gpio6.IO[6]
139	USB_OTG_DP
140	A22	gpio2.IO[16]
141	USB_OTG_DN
142	A21	gpio2.IO[17]
143	USB_HOST_DP
144	A20	gpio2.IO[18]
145	USB_HOST_DN
146	A19 / PCM_IN	gpio2.IO[19]	gpio5.IO[1]
147	GND
148	VCC
149	D00 / DDC_SDA	gpio3.IO[16]
150	D16 / LCD_D16	gpio5.IO[10]
151	D01	gpio3.IO[17]
152	D17 / LCD_D17	gpio5.IO[11]
153	D02	gpio3.IO[18]
154	D18 / PCIE_WAKE	gpio6.IO[7]	gpio3.IO[13]
155	D03	gpio3.IO[19]
156	D19 / LDO
157	D04	gpio3.IO[20]
158	D20 / PCIE_CLKN
159	D05 / SPDIF_IN	gpio3.IO[21]	gpio5.IO[4]
160	D21 / PCIE_CLKP
161	D06 / SPDIF_OUT	gpio3.IO[22]	gpio5.IO[3]
162	D22 / PCIE_TXP
163	D07 / SPDIF_EXT_CLK	gpio3.IO[23]	gpio5.IO[5]
164	D23 / PCIE_TXN
165	D08	gpio3.IO[24]
166	D24 / PCIE_RXP
167	D09	gpio3.IO[25]
168	D25 / PCIE_RXN
169	D10	gpio3.IO[26]
170	LCD_D21	gpio5.IO[15]
171	D11	gpio3.IO[27]
172	LCD_D20	gpio5.IO[14]
173	D12	gpio3.IO[28]
174	LCD_D19	gpio5.IO[13]
175	D13	gpio3.IO[29]
176	LCD_D18	gpio5.IO[12]
177	D14	gpio3.IO[30]
178	LCD_D23	gpio5.IO[17]
179	D15	gpio3.IO[31]
180	LCD_D22	gpio5.IO[16]
181	GND
182	VCC
183	ETH_LINK_AKT
184	A18 / PCM_OUT	gpio2.IO[20]	gpio4.IO[30]
185	ETH_SPEED
186	A17 / PCM_CLK	gpio2.IO[21]	gpio4.IO[29]
187	ETH_TXN
188	A16 / PCM_SYNC	gpio2.IO[22]	gpio4.IO[28]
189	ETH_TXP
190	SD2_CMD	gpio1.IO[11]	gpio2.IO[14]
191	ETH_GND
192	SD2_DATA0	gpio1.IO[15]	gpio2.IO[15]
193	ETH_RXN
194	I2C2_SDA	gpio4.IO[13]	gpio5.IO[17]
195	ETH_RXP
196	I2C2_SCL	gpio4.IO[12]	gpio5.IO[16]
197	GND
198	VCC
199	GND
200	VCC RTC