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Description
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[HB GPIO] GPIO, or General-Purpose Input/Output is a mechanism that allows a computing board to provide electrical contacts for signalling to a wide range of external devices. These pins allow commerical and hobbyist projects to do things like communicate with a “breakout board”, or individual physical modules – like a motor.
GPIO interfaces are different than other capabilities on a circuit board (like LVDS or the RTC integration) in that they provide a non-specific electrical interface. While these other interfaces have a set specification and set capability for an intended use (connecting to an LCD panel or a real-time clock, in the cited examples respectively) GPIO pins are used at the developer’s discretion. You could connect a motor. Or a temperature sensor. Or a lock solenoid. Or any one of millions of other device combinations for bringing information into the system – or sending information out from the HummingBoard device.
Pin header schematics
26 pin header
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GPIO Header Pinout
Header Pin | Pad Name (Default) | GPIO Name | Linux GPIO Number (*) |
|---|---|---|---|
J2 [pin 1] | 3.3V | - | |
J2 [pin 2] | 5V | - | |
J2 [pin 3] | I2C_SDA | # | |
J2 [pin 4] | 5V | - | |
J2 [pin 5] | I2C_SCL | # | |
J2 [pin 6] | GND | - | |
J2 [pin 7] | GPIO 1 | 1 | |
J2 [pin 8] | UART TX | # | |
J2 [pin 9] | GND | - | |
J2 [pin 10] | UART RX | # | |
J2 [pin 12] | GPIO 72 | GPIO3_IO08 | 72 |
J2 [pin 13] | GPIO 71 | 71 | |
J2 [pin 14] | GND | - | |
J2 [pin 15] | GPIO 10 | 10 | |
J2 [pin 16] | GPIO 194 | 194 | |
J2 [pin 17] | 3.3V | - | |
J2 [pin 18] | GPIO 195 | 195 | |
J2 [pin 19] | SPI_MOSI | # | |
J2 [pin 20] | GND | - | |
J2 [pin 21] | SPI_MISO | # | |
J2 [pin 22] | GPIO 67 | 67 | |
J2 [pin 23] | SPI_SCLK | # | |
J2 [pin 24] | ECSPI2_SS0 | # | |
J2 [pin 25] | GND | - | |
J2 [pin 26] | ECSPI2_SS1 | # |
Pins 16 and 18 are actually SD3_CMD and SD3_CLK signals that can be muxed to support flex can TX/RX interface (i.e. those can be connected to an external CAN).
(*) SPI and I2C & UART can also be muxed to be GPIO
Accessing GPIO from Linux user space
General
Please have a look at WiringX, which also supports the Hummingboard:
Manual
The external GPIOs are available under the /sys/class/gpio folder in Linux.
To control on the GPIO pins you need to calculate the GPIO number XX (*) and run the commands below:Get the current list of reserved GPIO
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> mount -t debugfs none /sys/kernel/debug
> cat /sys/kernel/debug/gpio |
Reserve GPIO pin
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# Export GPIO XX
echo XX > /sys/class/gpio/export
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Set
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GPIO
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pin
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Direction
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echo "out" > /sys/class/gpio/gpioXX/direction # or echo "in" > /sys/class/gpio/gpioXX/direction # |
Set
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the
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value
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of
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an
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output
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pin
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echo 1 > /sys/class/gpio/gpioXX/value # or echo 0 > /sys/class/gpio/gpioXX/value # |
Get
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the
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value
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of
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an
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input
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pin
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cat > /sys/class/gpio/gpioXX/value
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Free GPIO pin
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# Unexport GPIO XX
echo XX > /sys/class/gpio/unexport
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You can To calculate the GPIO number XX:
XX = linux gpio number = (gpio_bank - 1) * 32 + gpio_bit
Example: to To calculate the GPIO number of pin header ####J2 [pin 12] Pad Name : GPIO3_IO08
GPIO Bank = #######3, GPIO bit = #######8
XX = ##############
Attached here the header schematics
26 pin header
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Header Pin
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Pad Name
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GPIO name
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Linux GPIO number
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J2 [pin 1]
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3.3V
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#
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J2 [pin 2]
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5V
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#
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J2 [pin 3]
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I2C_SDA
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#
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J2 [pin 4]
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5V
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#
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J2 [pin 5]
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I2C_SCL
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#
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J2 [pin 6]
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GND
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#
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J2 [pin 7]
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GPIO 1
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#
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J2 [pin 8]
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UART TX
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#
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J2 [pin 9]
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GND
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#
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J2 [pin 10]
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UART RX
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#
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J2 [pin 12]
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GPIO 72
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#
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J2 [pin 13]
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GPIO 71
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#
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J2 [pin 14]
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GND
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#
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J2 [pin 15]
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GPIO 10
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#
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J2 [pin 16]
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GPIO 194*
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#
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J2 [pin 17]
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3.3V
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#
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J2 [pin 18]
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GPIO 195*
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#
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J2 [pin 19]
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SPI_MOSI
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#
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J2 [pin 20]
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GND
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#
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J2 [pin 21]
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SPI_MISO
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#
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J2 [pin 22]
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GPIO 67
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#
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J2 [pin 23]
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SPI_SCLK
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#
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J2 [pin 24]
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ECSPI2_SS0
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#
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J2 [pin 25]
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GND
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#
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J2 [pin 26]
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ECSPI2_SS1
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= (3 - 1) * 32 + 8 = 72
You can take the GPIO Number from the above table (*)
Serial UART port access
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The UART port for debug can be accessed on the 26 pin header as follows –
Pin 6/9/14/20/25 GND
Pin 1 3.3V
Pin 8 buffered i.MX6 UART TX – pulled up to 3.3v
Pin 10 buffered i.MX6 UART RX – pulled up to 3.3v
Notice that the pin number starts as pin #1 on the edge of the board, towards the micro-USB connector; then number #2 is the one towards the corner of the board.
External Links and References
IMX6 Software Development/Drivers
IMX6 Som Documents
wiringHB