GPIO pins - Revision history

CityK: /* How GPIO pins work */ more minor edits; rephrasing and clarifying

2010-04-18T19:57:06Z

How GPIO pins work: more minor edits; rephrasing and clarifying

← Older revision		Revision as of 19:57, 18 April 2010
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	In others cases, GPIOs are arranged into very simple groups, typically of 8 pins – known as a GPIO port - that can be switched as a group to either input or output.		In others cases, GPIOs are arranged into very simple groups, typically of 8 pins – known as a GPIO port - that can be switched as a group to either input or output.

-	The input and output voltages are typically, though not universally limited to the supply voltage of the ~~device with~~ the GPIOs on, and ~~may be damaged by greater~~ voltages. ~~Some~~ GPIOs have 5V tolerant inputs - even on low supply voltages (2V), ~~the device~~ can accept 5V without damage.	+	The input and output voltages are typically, though not universally, limited to the supply voltage of the IC upon which the GPIOs reside, and usage of voltages greater then that may cause damage to the chip. Though, in the case of some ICs, the GPIOs have 5V tolerant inputs, such that even when the IC itself has a low supply voltages (2V), it can accept the greater voltage (5V) on the GPIO pin input without damage.

	In some cases, GPIOs may be configurable to produce CPU interrupts and be able to use Direct Memory Access to move large quantities of data efficiently into or out of the device.		In some cases, GPIOs may be configurable to produce CPU interrupts and be able to use Direct Memory Access to move large quantities of data efficiently into or out of the device.

CityK: /* How GPIO pins work */

2010-04-18T19:42:07Z

How GPIO pins work

← Older revision		Revision as of 19:42, 18 April 2010
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	==How GPIO pins work==		==How GPIO pins work==
-	A GPIO pin on an IC is typically connected to some other chip, and performs some function by changing its state. GPIO pins can act as either an:	+	A GPIO pin on an IC is typically connected to some other chip, and performs some function by reading or changing its state. GPIO pins can act as either an:
	* input - to read digital signals from a circuit; that is, when configured for input mode, they read the current state as either "high" or "low"		* input - to read digital signals from a circuit; that is, when configured for input mode, they read the current state as either "high" or "low"
	* output - to control or signal other devices attached to the IC and, as such, the pins are configured to be “high” or “low” when in output mode		* output - to control or signal other devices attached to the IC and, as such, the pins are configured to be “high” or “low” when in output mode

CityK: /* How GPIO pins work */ a little clean up

2010-04-18T19:40:07Z

How GPIO pins work: a little clean up

← Older revision		Revision as of 19:40, 18 April 2010
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	==How GPIO pins work==		==How GPIO pins work==
-	A GPIO pin on an IC is typically connected to some other chip, and performs some function by changing its state. GPIO pins can ~~be configured~~ to ~~be “high” or “low”~~ when ~~in output~~ mode, ~~or you can~~ read the current state as high or low ~~when~~ configured ~~for input~~ mode.	+	A GPIO pin on an IC is typically connected to some other chip, and performs some function by changing its state. GPIO pins can act as either an:
		+	* input - to read digital signals from a circuit; that is, when configured for input mode, they read the current state as either "high" or "low"
		+	* output - to control or signal other devices attached to the IC and, as such, the pins are configured to be “high” or “low” when in output mode

-	~~GPIO pins on an IC can act as either an:~~
-	* input - to read digital signals from a circuit
-	* output - to control or signal other devices attached to the IC.
	Usually each GPIO pin is individually configurable as either an input or output -- each pin can be setup flexibly to accept or source different logic voltages, with configurable drive strengths and pull up/downs.		Usually each GPIO pin is individually configurable as either an input or output -- each pin can be setup flexibly to accept or source different logic voltages, with configurable drive strengths and pull up/downs.
	In others cases, GPIOs are arranged into very simple groups, typically of 8 pins – known as a GPIO port - that can be switched as a group to either input or output.		In others cases, GPIOs are arranged into very simple groups, typically of 8 pins – known as a GPIO port - that can be switched as a group to either input or output.

-	The input and output voltages are typically, though not universally limited to the supply voltage of the device with the GPIOs on, and may be damaged by greater voltages.	+	The input and output voltages are typically, though not universally limited to the supply voltage of the device with the GPIOs on, and may be damaged by greater voltages. Some GPIOs have 5V tolerant inputs - even on low supply voltages (2V), the device can accept 5V without damage.
-	Some GPIOs have 5V tolerant inputs - even on low supply voltages (2V), the device can accept 5V without damage.	+
	In some cases, GPIOs may be configurable to produce CPU interrupts and be able to use Direct Memory Access to move large quantities of data efficiently into or out of the device.		In some cases, GPIOs may be configurable to produce CPU interrupts and be able to use Direct Memory Access to move large quantities of data efficiently into or out of the device.

CityK: /* Programming GPIO pins */ minor rephrasing

2010-04-18T19:32:18Z

Programming GPIO pins: minor rephrasing

← Older revision		Revision as of 19:32, 18 April 2010
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	* BtSpy - http://btwincap.sourceforge.net/custom.html		* BtSpy - http://btwincap.sourceforge.net/custom.html

-	In addition, a good old magnifying glass is a great tool. GPIO inputs are just pins on ~~video chip~~ and remote or mux switch or audio chip ~~should be standalone~~. ~~Find them on a board and use a magnifier. You should find~~ the ~~track between them and from a datasheet~~ you'll	+	In addition, a good old magnifying glass is a great tool. GPIO inputs are, after all, just pins on an IC that will be connected in circuit to an external component. For example, you should be able to find and track the traces on the device's printed circuit board between the GPIO pins on an interface chipset and, say, a remote controller or mux switch or audio chip etc. In conjunction with the datasheets for these ICs you'll likely be able to easily find the correct GPIO values.
-	easily find the correct GPIO values.	+

	====GPIOs of SAA713x====		====GPIOs of SAA713x====

CityK: more minor changes to the big scary warnign

2010-04-18T19:21:02Z

more minor changes to the big scary warnign

← Older revision		Revision as of 19:21, 18 April 2010
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	* Unused Pins are usually programmed as inputs.		* Unused Pins are usually programmed as inputs.

-	{{Box Warning\|~~Playing~~ with GPIO-pins may damage your device!	+	{{Box Warning\|Haphazardly playing with or mis-configuring GPIO-pins may damage your device!
	'''If you undertake any modifications, we take no responsibility for any damage caused or which may be incurred to your device through the process. You proceed entirely at your own risk'''}}		'''If you undertake any modifications, we take no responsibility for any damage caused or which may be incurred to your device through the process. You proceed entirely at your own risk'''}}

CityK: minor update to big scary message

2010-04-18T19:14:43Z

minor update to big scary message

← Older revision		Revision as of 19:14, 18 April 2010
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	* Unused Pins are usually programmed as inputs.		* Unused Pins are usually programmed as inputs.

-	~~<div style="vertical-align:top; margin:0; border:1px solid #6289AB; padding:0.5em; background-color:#ffffff">~~	+	{{Box Warning\|Playing with GPIO-pins may damage your device!
-	{\|~~valign=top cellpadding=0 cellspacing=5 width=100%~~	+	'''If you undertake any modifications, we take no responsibility for any damage caused or which may be incurred to your device through the process. You proceed entirely at your own risk'''}}
-	~~\| [[Image:Exclaimation.png\|75px]]~~	+
-	~~\| '''IMPORTANT NOTICE:~~ Playing with GPIO-pins may damage your ~~card~~'''.	+
-	\|}	+
-	~~</div>~~	+

	Two Windows based utilities that can be handy in the process of determining what to program for GPIO values in device definitions are:		Two Windows based utilities that can be handy in the process of determining what to program for GPIO values in device definitions are:

CityK: minor changes; spelling

2010-04-18T17:39:01Z

minor changes; spelling

← Older revision		Revision as of 17:39, 18 April 2010
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	* Sometimes, 2 or 3 of them are used to control an audio multiplexer found elsewhere on the device. That is especially true for bt878-based cards, as that particular chip lacks a built-in audio mux and therefore must rely upon external components to provide such functionality.		* Sometimes, 2 or 3 of them are used to control an audio multiplexer found elsewhere on the device. That is especially true for bt878-based cards, as that particular chip lacks a built-in audio mux and therefore must rely upon external components to provide such functionality.

-	* IR receiver chips are also often connected via GPIO pins (though, thats not the only way, as [[I²C Protocol\|I²C]] is common as well, and some ~~inferface~~ chipsets, like the cx2388x, have built-in support for IR signal sampling).	+	* IR receiver chips are also often connected via GPIO pins (though, thats not the only way, as [[I²C Protocol\|I²C]] is common as well, and some interface chipsets, like the cx2388x, have built-in support for IR signal sampling).

	* Sometimes it is possible to reset external chips via GPIO. For example, bt878-designs with a msp34xx audio processor usually have the msp34xx reset line linked to one of the GPIO pins. As another example, in the case of the [[Hauppauge WinTV-HVR-950]] device, one of the GPIO pins on its em28xx bridge is connected to the “RESET” pin on the xc3028 tuner. Setting the state of the GPIO pin to low momentarily and then high again has the effect of resetting the chip to a known state. <br> It’s also worth noting that holding a chip in reset is often done as a power management measure, which is why you can see driver problems communicating with certain chips if the GPIOs are improperly configured. This sort of power management measure becomes particularly important on USB devices, where there is often not enough power available on the USB bus to have both the analog components and the digital components powered up at the same time.		* Sometimes it is possible to reset external chips via GPIO. For example, bt878-designs with a msp34xx audio processor usually have the msp34xx reset line linked to one of the GPIO pins. As another example, in the case of the [[Hauppauge WinTV-HVR-950]] device, one of the GPIO pins on its em28xx bridge is connected to the “RESET” pin on the xc3028 tuner. Setting the state of the GPIO pin to low momentarily and then high again has the effect of resetting the chip to a known state. <br> It’s also worth noting that holding a chip in reset is often done as a power management measure, which is why you can see driver problems communicating with certain chips if the GPIOs are improperly configured. This sort of power management measure becomes particularly important on USB devices, where there is often not enough power available on the USB bus to have both the analog components and the digital components powered up at the same time.
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	* Sometimes external chips can be enabled/disabled via GPIO. saa7134-based cardbus devices often have the tuner chip disabled, it's impossible to see the device on the i2c bus without waking it up by programming the correct GPIO pin. Probably done to power-down the tuner when unused for a longer battery life. For example, the Terratec Cinergy 400TV mobile uses GPIO 18 to switch the tuner on (0) or off (1).		* Sometimes external chips can be enabled/disabled via GPIO. saa7134-based cardbus devices often have the tuner chip disabled, it's impossible to see the device on the i2c bus without waking it up by programming the correct GPIO pin. Probably done to power-down the tuner when unused for a longer battery life. For example, the Terratec Cinergy 400TV mobile uses GPIO 18 to switch the tuner on (0) or off (1).

-	* Other common uses of GPIO pins include connecting it to the power supply on a board to cut off power to certain ~~peripherial~~ components, or controlling whether a low noise amplifier (LNA) connected to the tuner is enabled.	+	* Other common uses of GPIO pins include connecting it to the power supply on a board to cut off power to certain peripheral components, or controlling whether a low noise amplifier (LNA) connected to the tuner is enabled.

	* It's also noteworthy that some of the GPIO lines can be used to trigger interrupts i.e. the video chip can raise an IRQ on the PCI bus on GPIO state changes.		* It's also noteworthy that some of the GPIO lines can be used to trigger interrupts i.e. the video chip can raise an IRQ on the PCI bus on GPIO state changes.

CityK: add the info from the wikipedia article (some of it is currently in verbatim, while others parts I have parsed/altered accordingly); other minor changes

2010-04-18T17:35:49Z

add the info from the wikipedia article (some of it is currently in verbatim, while others parts I have parsed/altered accordingly); other minor changes

← Older revision		Revision as of 17:35, 18 April 2010
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	A GPIO pin on an IC is typically connected to some other chip, and performs some function by changing its state. GPIO pins can be configured to be “high” or “low” when in output mode, or you can read the current state as high or low when configured for input mode.		A GPIO pin on an IC is typically connected to some other chip, and performs some function by changing its state. GPIO pins can be configured to be “high” or “low” when in output mode, or you can read the current state as high or low when configured for input mode.

-	~~''also see~~ the ~~wikipedia article for info that should~~ be ~~parsed~~ into ~~this section''~~	+	GPIO pins on an IC can act as either an:
-	~~<br>~~	+	* input - to read digital signals from a circuit
		+	* output - to control or signal other devices attached to the IC.
		+	Usually each GPIO pin is individually configurable as either an input or output -- each pin can be setup flexibly to accept or source different logic voltages, with configurable drive strengths and pull up/downs.
		+	In others cases, GPIOs are arranged into very simple groups, typically of 8 pins – known as a GPIO port - that can be switched as a group to either input or output.
		+
		+	The input and output voltages are typically, though not universally limited to the supply voltage of the device with the GPIOs on, and may be damaged by greater voltages.
		+	Some GPIOs have 5V tolerant inputs - even on low supply voltages (2V), the device can accept 5V without damage.
		+	In some cases, GPIOs may be configurable to produce CPU interrupts and be able to use Direct Memory Access to move large quantities of data efficiently into or out of the device.

	==GPIO pins within the context of V4L-DVB devices==		==GPIO pins within the context of V4L-DVB devices==
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	====GPIOs of BT8x8====		====GPIOs of BT8x8====
-	Here's how to program gpio for card definitions inside bttv-cards.c using RegSpy~~, included with DScaler - http://dscaler~~.~~org Another~~ utility ~~that can come in~~ handy during this process ~~is BtSpy - http://btwincap.sourceforge.net/custom~~.~~html~~	+	Here's how to program gpio for card definitions inside bttv-cards.c using RegSpy. The BtSpy utility is also handy during this process.

	Attach RegSpy to your TV App. Switch some channels around in analog video mode. Take note of the following values:		Attach RegSpy to your TV App. Switch some channels around in analog video mode. Take note of the following values:
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	====GPIOs of CX2388x====		====GPIOs of CX2388x====
-	To program gpio for card definitions inside cx88-cards.c ~~using RegSpy, included with DScaler - http://dscaler.org~~ , ~~Follow~~ the directions above for ~~the~~ bt8xx cards, but you'll want to consider a different set of values, namely MO_GPx_IO (x=0 to 3). The relevant part of RegSpy's output will look basically like this:	+	To program gpio for card definitions inside cx88-cards.c , follow the directions above for using RegSpy with bt8xx cards but you'll want to consider a different set of values, namely MO_GPx_IO (x=0 to 3). The relevant part of RegSpy's output will look basically like this:

	MO_GP0_IO: 000000ff (00000000 00000000 00000000 11111111)		MO_GP0_IO: 000000ff (00000000 00000000 00000000 11111111)

CityK: /* GPIO pins within the context of V4L-DVB devices */ minor arrangement

2010-04-12T22:16:00Z

GPIO pins within the context of V4L-DVB devices: minor arrangement

← Older revision		Revision as of 22:16, 12 April 2010
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	==GPIO pins within the context of V4L-DVB devices==		==GPIO pins within the context of V4L-DVB devices==
-	It is quite common for the [[interface chipsets\|interface chipset]] of a V4L-DVB device to be equipped with GPIO pins. For example, interface chipsets/Video decoder chips like the [[NXP SAA713x Family\|SAA713x]] or the [[PCI_interface_chipsets_used_for_v4l_cards\|BT8x8]] have a number of I/O pins that are not used by the video decoder itself. In practical terms, for tuner products, it is pretty rare for GPIO pins to be configured as inputs. [Side note: a related terminology to GPIO is GPO – which stands for “General Purpose Output” and is the same thing as a GPIO but functions as output only].	+	It is quite common for the [[interface chipsets\|interface chipset]] of a V4L-DVB device to be equipped with GPIO pins. For example, interface chipsets/Video decoder chips like the [[NXP SAA713x Family\|SAA713x]] or the [[PCI_interface_chipsets_used_for_v4l_cards\|BT8x8]] have a number of I/O pins that are not used by the video decoder itself.

	Typically what the GPIO pins are used for:		Typically what the GPIO pins are used for:
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	* It's also noteworthy that some of the GPIO lines can be used to trigger interrupts i.e. the video chip can raise an IRQ on the PCI bus on GPIO state changes.		* It's also noteworthy that some of the GPIO lines can be used to trigger interrupts i.e. the video chip can raise an IRQ on the PCI bus on GPIO state changes.

-	This list likely isn't complete, but it should give an idea what GPIO pins are used for in the context of V4L-DVB devices. Also keep in mind that the GPIO pins might be completely unused -- it's a choice entirely up to the device manufacturer.	+	This list likely isn't complete, but it should give an idea what GPIO pins are used for in the context of V4L-DVB devices. Also keep in mind that the GPIO pins might be completely unused -- it's a choice entirely up to the device manufacturer. Note: In practical terms, for tuner products, it is pretty rare for GPIO pins to be configured as inputs. [Side note: a related terminology to GPIO is GPO – which stands for “General Purpose Output” and is the same thing as a GPIO but functions as output only].

	===Programming GPIO pins===		===Programming GPIO pins===

CityK: /* GPIO pins within the context of V4L-DVB devices */ minor edits

2010-04-12T22:13:01Z

GPIO pins within the context of V4L-DVB devices: minor edits

← Older revision		Revision as of 22:13, 12 April 2010
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	* IR receiver chips are also often connected via GPIO pins (though, thats not the only way, as [[I²C Protocol\|I²C]] is common as well, and some inferface chipsets, like the cx2388x, have built-in support for IR signal sampling).		* IR receiver chips are also often connected via GPIO pins (though, thats not the only way, as [[I²C Protocol\|I²C]] is common as well, and some inferface chipsets, like the cx2388x, have built-in support for IR signal sampling).

-	* Sometimes it is possible to reset external chips via GPIO. For example, bt878-designs with a msp34xx audio processor usually have the msp34xx reset line linked to one of the GPIO pins. As another example, in the case of the [[Hauppauge WinTV-HVR-950]] device, one of the GPIO pins on its em28xx bridge is connected to the “RESET” pin on the xc3028 tuner. Setting the state of the GPIO pin to low momentarily and then high again has the effect of resetting the chip to a known state.	+	* Sometimes it is possible to reset external chips via GPIO. For example, bt878-designs with a msp34xx audio processor usually have the msp34xx reset line linked to one of the GPIO pins. As another example, in the case of the [[Hauppauge WinTV-HVR-950]] device, one of the GPIO pins on its em28xx bridge is connected to the “RESET” pin on the xc3028 tuner. Setting the state of the GPIO pin to low momentarily and then high again has the effect of resetting the chip to a known state. <br> It’s also worth noting that holding a chip in reset is often done as a power management measure, which is why you can see driver problems communicating with certain chips if the GPIOs are improperly configured. This sort of power management measure becomes particularly important on USB devices, where there is often not enough power available on the USB bus to have both the analog components and the digital components powered up at the same time.
-	It’s also worth noting that holding a chip in reset is often done as a power management measure, which is why you can see driver problems communicating with certain chips if the GPIOs are improperly configured. This sort of power management measure becomes particularly important on USB devices, where there is often not enough power available on the USB bus to have both the analog components and the digital components powered up at the same time.	+

	* Sometimes external chips can be enabled/disabled via GPIO. saa7134-based cardbus devices often have the tuner chip disabled, it's impossible to see the device on the i2c bus without waking it up by programming the correct GPIO pin. Probably done to power-down the tuner when unused for a longer battery life. For example, the Terratec Cinergy 400TV mobile uses GPIO 18 to switch the tuner on (0) or off (1).		* Sometimes external chips can be enabled/disabled via GPIO. saa7134-based cardbus devices often have the tuner chip disabled, it's impossible to see the device on the i2c bus without waking it up by programming the correct GPIO pin. Probably done to power-down the tuner when unused for a longer battery life. For example, the Terratec Cinergy 400TV mobile uses GPIO 18 to switch the tuner on (0) or off (1).
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	===Programming GPIO pins===		===Programming GPIO pins===
-	~~Unused Pins are usually programmed as inputs.~~	+	GPIOs can not be read_from/written_to from user space. There is no IOCTL for them. They can only be used from within the kernel driver.
-		+
-	~~These~~ GPIOs can not be ~~read~~/~~written~~ from user space. There is no IOCTL for them. They can only be used from within the kernel driver.	+

	Because each device manufacturer can do with GPIO pins whatever they want, it is hard to answer questions like "What do I have to fill into these GPIO fields when adding a new card?", because there simply is no general answer to that question; it completely depends on the board design. Some hopefully useful hints:		Because each device manufacturer can do with GPIO pins whatever they want, it is hard to answer questions like "What do I have to fill into these GPIO fields when adding a new card?", because there simply is no general answer to that question; it completely depends on the board design. Some hopefully useful hints:
-	* First ignore them completely. Especially with non-bt878 cards (saa7134, cx88 drivers) they might not be used at all or at least not needed for the basic functionality of the board.	+	* First, ignore them completely. Especially with non-bt878 cards (saa7134, cx88 drivers) they might not be used at all or at least not needed for the basic functionality of the board.
	* Failing that check out whenever there are already entries for other cards from the same vendor and try these settings. Vendors usually don't redesign everything from scratch for a new card, so chances are good that a identical or very similar configuration works fine.		* Failing that check out whenever there are already entries for other cards from the same vendor and try these settings. Vendors usually don't redesign everything from scratch for a new card, so chances are good that a identical or very similar configuration works fine.
		+	* Unused Pins are usually programmed as inputs.

	<div style="vertical-align:top; margin:0; border:1px solid #6289AB; padding:0.5em; background-color:#ffffff">		<div style="vertical-align:top; margin:0; border:1px solid #6289AB; padding:0.5em; background-color:#ffffff">