GPIO - Revision history

Calculus: Added category

2011-10-28T02:18:39Z

Added category

Peter Huewe: /* LeopoardBoard 365 GPIO 0 connection */ spellcheck

2011-04-13T05:14:30Z

‎LeopoardBoard 365 GPIO 0 connection: spellcheck

Tfischer at 20:31, 12 April 2011

2011-04-12T20:31:59Z

Tfischer at 20:31, 12 April 2011

2011-04-12T20:31:36Z

Tfischer at 20:13, 12 April 2011

2011-04-12T20:13:29Z

Tfischer at 20:10, 12 April 2011

2011-04-12T20:10:14Z

FransMeulenbroeks: added wikipedia ref

2008-11-17T20:16:43Z

added wikipedia ref

Prpplague at 18:34, 24 September 2007

2007-09-24T18:34:34Z

New page

General Purpose Input or Output

a generic i/o line on a SoC is often refered to as a GPIO. by definition a GPIO is a line that can be used as an input or output, however many times vendors will as refer to lines that support external interrupts as GPIO as well.

← Older revision		Revision as of 02:18, 28 October 2011
Line 155:		Line 155:
	GPIOs 96-103, DaVinci:		GPIOs 96-103, DaVinci:
	</pre>		</pre>
		+
		+	[[Category:Hardware]]

@@ Line 67: / Line 67: @@
 The following example uses LeopardBoard 365.
-==== LeopoardBoard 365 GPIO 0 connection ====
+==== LeopardBoard 365 GPIO 0 connection ====
 On the LeopardBoard 365, the only GPIO I could find that was usable for interrupt input is GPIO0, also called CMOS_TRIGGER in the schematics.  In looking at the schematics resistor R12 is not loaded and one of the pads connects to CMOS_TRIGGER.  This R12 pad is the one closest to R11.  If you hold the LeopardBoard 365 with the SD card slot facing you and rotate the board until the SD card slot is on the bottom edge, the the R12 pads are to the right of J6 and to the left of the SD card slot upper left corner.

← Older revision		Revision as of 20:31, 12 April 2011
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−	General Purpose Input or Output: a generic I/O line on a SoC is often referred to as a GPIO. By definition a GPIO is a line that can be used as an input or output> In some cases vendors will to a signal that support external interrupts as a GPIO line as well.	+	General Purpose Input or Output: a generic I/O line on a SoC is often referred to as a GPIO. By definition a GPIO is a line that can be used as an input or output. In some cases vendors will to a signal that support external interrupts as a GPIO line as well.

	== References ==		== References ==

← Older revision		Revision as of 20:31, 12 April 2011
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	<pre>		<pre>
		+	/ # mount -t debugfs none /sys/kernel/debug
		+	/ # cat /sys/kernel/debug/gpio
		+	GPIOs 0-31, DaVinci:
		+	gpio-22 (sysfs ) in lo
		+	gpio-23 (sysfs ) in lo
		+	gpio-24 (sysfs ) in lo
		+	gpio-25 (sysfs ) in lo

		+	GPIOs 32-63, DaVinci:
		+	gpio-57 (sysfs ) out lo
		+
		+	GPIOs 64-95, DaVinci:
		+	gpio-66 (usb ) out lo
		+
		+	GPIOs 96-103, DaVinci:
	</pre>		</pre>

@@ Line 1: / Line 1: @@
-General Purpose Input or Output
+General Purpose Input or Output: a generic I/O line on a SoC is often referred to as a GPIO.  By definition a GPIO is a line that can be used as an input or output>  In some cases vendors will to a signal that support external interrupts as a GPIO line as well.
-−
-a generic i/o line on a SoC is often refered to as a GPIO. by definition a GPIO is a line that can be used as an input  or output, however many times vendors will as refer to lines that support external interrupts as GPIO as well.
 == References ==
@@ Line 71: / Line 69: @@
 ==== LeopoardBoard 365 GPIO 0 connection ====
-On the LeopardBoard 365, the only GPIO I could find that was usable for interrupt input is GPIO0, also called CMOS_TRIGGER in the schematics.  In looking at the schematics resistor R12 is not loaded and one of the pads connects to CMOS_TRIGGER.  This R12 pad is the one closest to R11.  If you hold the leopardboard 365 with the SD card slot facing you and rotate the board until the SD card slot is on the bottom edge, the the R12 pads are to the right of J6 and to the left of the SD card slot upper left corner.
+On the LeopardBoard 365, the only GPIO I could find that was usable for interrupt input is GPIO0, also called CMOS_TRIGGER in the schematics.  In looking at the schematics resistor R12 is not loaded and one of the pads connects to CMOS_TRIGGER.  This R12 pad is the one closest to R11.  If you hold the LeopardBoard 365 with the SD card slot facing you and rotate the board until the SD card slot is on the bottom edge, the the R12 pads are to the right of J6 and to the left of the SD card slot upper left corner.
 ==== Using poll() to monitor for GPIO 0 change ====
-The [[gpio-int-test.c]] program shows one way of using the sysfs file /sys/class/gpio/gpio0/value to block program execution using poll() until the input level on GPIO0 changes.  The tricky part was figuring out to use POLLPRI instead of POLLIN as the event to monitor.  You must have GPIO support in sysfs for this program to work (or you will not see the /sys/class/gpio directory).
+The gpio-int-test.c program shows one way of using the sysfs file /sys/class/gpio/gpio0/value to block program execution using poll() until the input level on GPIO0 changes.  The tricky part was figuring out to use POLLPRI instead of POLLIN as the event to monitor.  You must have GPIO support in sysfs for this program to work (or you will not see the /sys/class/gpio directory).

← Older revision		Revision as of 20:10, 12 April 2011
Line 3:		Line 3:
	a generic i/o line on a SoC is often refered to as a GPIO. by definition a GPIO is a line that can be used as an input or output, however many times vendors will as refer to lines that support external interrupts as GPIO as well.		a generic i/o line on a SoC is often refered to as a GPIO. by definition a GPIO is a line that can be used as an input or output, however many times vendors will as refer to lines that support external interrupts as GPIO as well.

−	~~See:~~ http://en.wikipedia.org/wiki/General_Purpose_Input/Output	+	== References ==
		+
		+	* http://en.wikipedia.org/wiki/General_Purpose_Input/Output
		+	* http://www.avrfreaks.net/wiki/index.php/Documentation:Linux/GPIO
		+	* http://bec-systems.com/site/281/how-to-implement-an-interrupt-driven-gpio-input-in-linux
		+	* http://www.spinics.net/lists/linux-newbie/msg01028.html
		+	* http://docs.blackfin.uclinux.org/doku.php?id=linux-kernel:drivers:gpio-sysfs
		+
		+	== Application space GPIO support ==
		+
		+	Linux GPIO support includes the ability to export GPIO control and status for use with applications using sysfs. No other driver can be using the GPIO of interest. Simple tools like ''cat'' and ''echo'' can be used to quickly read the current value of a GPIO input or to set the level of a GPIO output.
		+
		+	=== Configure the kernel for GPIO support in sysfs ===
		+
		+	You likely need to enable GPIO support in sysfs before GPIOs are accessible from application space.
		+
		+	<pre>
		+	Symbol: GPIO_SYSFS [=y]
		+	Prompt: /sys/class/gpio/... (sysfs interface)
		+	Defined at drivers/gpio/Kconfig:51
		+	Depends on: GPIOLIB && SYSFS && EXPERIMENTAL
		+	Location:
		+	-> Kernel configuration
		+	-> Device Drivers
		+	-> GPIO Support (GPIOLIB [=y])
		+	</pre>
		+
		+	=== Enable GPIO from application space ===
		+
		+	In this example, GPIO 22 is make available (exported) to application space.
		+
		+	<pre>
		+	GPIO=22
		+
		+	cd /sys/class/gpio
		+	ls
		+	echo $GPIO > export
		+	ls
		+	</pre>
		+
		+	Notice on the first ''ls'' that ''gpio22'' doesn't exist, but does after you export GPIO 22 to user space.
		+
		+	<pre>
		+	cd /sys/class/gpio/gpio$GPIO
		+	ls
		+	</pre>
		+
		+	There are files to set the direction and retrieve the current value.
		+
		+	<pre>
		+	echo "in" > direction
		+	cat value
		+	</pre>
		+
		+	You can configure the GPIO for output and set the value as well.
		+
		+
		+	<pre>
		+	echo "out" > direction
		+	echo 1 > value
		+	</pre>
		+
		+	=== GPIO interrupts from user space ===
		+
		+	The following example uses LeopardBoard 365.
		+
		+	==== LeopoardBoard 365 GPIO 0 connection ====
		+
		+	On the LeopardBoard 365, the only GPIO I could find that was usable for interrupt input is GPIO0, also called CMOS_TRIGGER in the schematics. In looking at the schematics resistor R12 is not loaded and one of the pads connects to CMOS_TRIGGER. This R12 pad is the one closest to R11. If you hold the leopardboard 365 with the SD card slot facing you and rotate the board until the SD card slot is on the bottom edge, the the R12 pads are to the right of J6 and to the left of the SD card slot upper left corner.
		+
		+	==== Using poll() to monitor for GPIO 0 change ====
		+
		+	The [[gpio-int-test.c]] program shows one way of using the sysfs file /sys/class/gpio/gpio0/value to block program execution using poll() until the input level on GPIO0 changes. The tricky part was figuring out to use POLLPRI instead of POLLIN as the event to monitor. You must have GPIO support in sysfs for this program to work (or you will not see the /sys/class/gpio directory).
		+
		+
		+	The [https://www.ridgerun.com/developer/wiki/index.php/Gpio-int-test.c gpio-int-test.c] program uses poll() to wake up every 3 seconds (using poll() timeout mechanism) at which time it prints a period. The poll() function is also watching for input from stdin and for an interrupt from GPIO 0.
		+
		+	Here is an example output. I started gpio-int to watch GPIO 0. I waited around 12 seconds (4 timeout periods), then pressed the letter 'a' twice followed by enter key. Then I shorted the haywire to 3.3V that is accessible on pin 5 on the JTAG connector. JTAG pin 5 is across from the JTAG missing pin). I exited the program using cntl-C.
		+
		+	<pre>
		+	/root # gpio-int 0
		+
		+	....aa
		+
		+	poll() stdin read 0xA61
		+
		+	poll() stdin read 0xA61
		+
		+	poll() stdin read 0xA0A
		+	..
		+	poll() GPIO 0 interrupt occurred (len 0)
		+
		+	poll() GPIO 0 interrupt occurred (len 0)
		+
		+	poll() GPIO 0 interrupt occurred (len 0)
		+
		+	poll() GPIO 0 interrupt occurred (len 0)
		+	..^C
		+	</pre>
		+
		+	== Viewing GPIO Configuration ==
		+
		+	For some SoCs (like TI's DM365) you can use [http://lwn.net/Articles/334546/ debugfs] to view the current GPIO configuration. You may also be able to use debugfs to see if the GPIO pin is multiplex as a GPIO or is dedicated to some other function.
		+
		+	Configure the kernel to enable debugfs:
		+
		+	<pre>
		+	Symbol: DEBUG_FS [=y]
		+	Prompt: Debug Filesystem
		+	Defined at lib/Kconfig.debug:77
		+	Depends on: SYSFS
		+	Location:
		+	-> Kernel configuration
		+	-> Kernel hacking
		+	</pre>
		+
		+	Boot the target hardware and mount debugfs:
		+
		+	<pre>
		+	mount -t debugfs none /sys/kernel/debug
		+	</pre>
		+
		+	Dump the GPIO configuration.
		+
		+	<pre>
		+	cat /sys/kernel/debug/gpio
		+	</pre>
		+
		+	Dump the pin multiplexing configuration.
		+
		+
		+	<pre>
		+	cat /sys/kernel/debug/omap_mux/board
		+	</pre>
		+
		+	An example output is:
		+
		+	<pre>
		+
		+	</pre>

← Older revision		Revision as of 20:16, 17 November 2008
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	a generic i/o line on a SoC is often refered to as a GPIO. by definition a GPIO is a line that can be used as an input or output, however many times vendors will as refer to lines that support external interrupts as GPIO as well.		a generic i/o line on a SoC is often refered to as a GPIO. by definition a GPIO is a line that can be used as an input or output, however many times vendors will as refer to lines that support external interrupts as GPIO as well.
		+
		+	See: http://en.wikipedia.org/wiki/General_Purpose_Input/Output