Quartz64 Model A using a PCF8574 - Revision history

CounterPillow: /* Device tree changes */

2023-04-02T21:39:41Z

Device tree changes

← Older revision		Revision as of 21:39, 2 April 2023
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	&i2c3 {		&i2c3 {
	#address-cells = <1>;		#address-cells = <1>;
	#size-cells = <0>;		#size-cells = <0>;
	status = "okay";		status = "okay";

CounterPillow: /* Device tree changes */ add needed cells properties to silence warnings

2023-04-02T21:39:30Z

Device tree changes: add needed cells properties to silence warnings

← Older revision		Revision as of 21:39, 2 April 2023
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	&i2c3 {		&i2c3 {
			#address-cells = <1>;
			#size-cells = <0>;
	status = "okay";		status = "okay";

Fxc: Headline fixes

2023-02-28T23:19:16Z

Headline fixes

← Older revision		Revision as of 23:19, 28 February 2023
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	In this article, we'll go over how to hook up a PCF8574 I<sup>2</sup>C I/O extender to a [[Quartz64]] Model A single-board computer, including what device tree changes to make and how to control it.		In this article, we'll go over how to hook up a PCF8574 I<sup>2</sup>C I/O extender to a [[Quartz64]] Model A single-board computer, including what device tree changes to make and how to control it.

	== Introduction ~~To The~~ PCF8574 ==		== Introduction to the PCF8574 ==

	The PCF8574 is a fairly ubiquitous GPIO extender that communicates through the I<sup>2</sup>C bus. You can find modules featuring it from many vendors on the usual marketplaces for cheap. It exposes 8 additional GPIO lines, and can be daisy chained to up to 8 devices, giving you an additional 64 GPIO outputs. Combining it with 8 PCF8574A modules will actually push this to a total of 128 GPIO outputs added to your board!		The PCF8574 is a fairly ubiquitous GPIO extender that communicates through the I<sup>2</sup>C bus. You can find modules featuring it from many vendors on the usual marketplaces for cheap. It exposes 8 additional GPIO lines, and can be daisy chained to up to 8 devices, giving you an additional 64 GPIO outputs. Combining it with 8 PCF8574A modules will actually push this to a total of 128 GPIO outputs added to your board!
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	The PCF8574 has a mainline Linux driver, meaning that you do not need to use I<sup>2</sup>C directly to control it; it will just appear as another <code>/dev/gpiochip''<n>''</code> device. A lot of Raspberry Pi focused guides for this chip get this precise thing wrong actually, and have the user manually fiddle with the bus.		The PCF8574 has a mainline Linux driver, meaning that you do not need to use I<sup>2</sup>C directly to control it; it will just appear as another <code>/dev/gpiochip''<n>''</code> device. A lot of Raspberry Pi focused guides for this chip get this precise thing wrong actually, and have the user manually fiddle with the bus.

	== Device ~~Tree Changes~~ ==		== Device tree changes ==

	To control the chip, you'll need to modify your board's device tree—a description of its hardware for devices that don't automatically enumerate—so that the kernel knows how to load the driver.		To control the chip, you'll need to modify your board's device tree—a description of its hardware for devices that don't automatically enumerate—so that the kernel knows how to load the driver.
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	There are two ways to edit your device tree. Either you can manually edit the base tree, or use device tree overlays.		There are two ways to edit your device tree. Either you can manually edit the base tree, or use device tree overlays.

	=== Device ~~Tree Overlays~~ ===		=== Device tree overlays ===

	On images/distributions which support device tree overlays in their build of u-boot and the device tree blobs, you can very simply write a device tree overlay. This means your base tree can still change as you update your OS, and there's no manual intervention needed on your part to have your modification be carried forward.		On images/distributions which support device tree overlays in their build of u-boot and the device tree blobs, you can very simply write a device tree overlay. This means your base tree can still change as you update your OS, and there's no manual intervention needed on your part to have your modification be carried forward.
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	If you want to use constants and includes in your device tree overlay, you'll need to pass the file through a C preprocessor with the appropriate include directories. For an example of a build system that does this, please consult [https://github.com/CounterPillow/overlay-examples/blob/main/Makefile the Makefile of CounterPillow's overlay-examples repository].		If you want to use constants and includes in your device tree overlay, you'll need to pass the file through a C preprocessor with the appropriate include directories. For an example of a build system that does this, please consult [https://github.com/CounterPillow/overlay-examples/blob/main/Makefile the Makefile of CounterPillow's overlay-examples repository].

	=== Manually ~~Editing The Base Tree~~ ===		=== Manually editing the base tree ===

	{{note\|You will need to install <tt>dtc</tt> for this.}}		{{note\|You will need to install <tt>dtc</tt> for this.}}
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	Now run <code>make dtbs</code> to compile the device tree. This should give you a <tt>arch/arm64/boot/dts/rockchip/rk3566-quartz64-a.dt'''b'''</tt>, which you can then copy into your <tt>/boot/dtbs/</tt> as for example <tt>quartz-with-pcf8574.dtb</tt> or something like that. Then, in your <tt>extlinux.conf</tt>, either add a new boot label or modify your existing boot labels <code>FDT</code> line to point towards this dtb file, with the path being relative to <tt>/boot</tt> and not to <tt>/</tt>.		Now run <code>make dtbs</code> to compile the device tree. This should give you a <tt>arch/arm64/boot/dts/rockchip/rk3566-quartz64-a.dt'''b'''</tt>, which you can then copy into your <tt>/boot/dtbs/</tt> as for example <tt>quartz-with-pcf8574.dtb</tt> or something like that. Then, in your <tt>extlinux.conf</tt>, either add a new boot label or modify your existing boot labels <code>FDT</code> line to point towards this dtb file, with the path being relative to <tt>/boot</tt> and not to <tt>/</tt>.

	== Daisy ~~Chaining~~ ==		== Daisy chaining ==

	As previously stated, you can hook up multiple of these modules onto the same bus. Here's how the device tree changes for this will look like:		As previously stated, you can hook up multiple of these modules onto the same bus. Here's how the device tree changes for this will look like:
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	To know which <tt>RK_PXX</tt> and which <tt>interrupt-parent</tt> correspond to which pin on the board, consult the schematics.		To know which <tt>RK_PXX</tt> and which <tt>interrupt-parent</tt> correspond to which pin on the board, consult the schematics.

	== Hooking ~~Up The Module~~ ==		== Hooking up the module ==

	Hook up SDA to pin number 3 of your board, and SCL to pin number 5. Connect GND to ground, e.g. pin number 9, and VCC to 3.3V, for example pin number 1. If you plan on using interrupts, connect the <tt>INT</tt> pin to whichever GPIO you defined as the interrupt pin.		Hook up SDA to pin number 3 of your board, and SCL to pin number 5. Connect GND to ground, e.g. pin number 9, and VCC to 3.3V, for example pin number 1. If you plan on using interrupts, connect the <tt>INT</tt> pin to whichever GPIO you defined as the interrupt pin.
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	'''TODO:''' Put photo of hooked up module here.		'''TODO:''' Put photo of hooked up module here.

	== Using ~~The~~ GPIOs ==		== Using the GPIOs ==

	Upon booting your board with your modified device tree blob, you should have an additional <tt>/dev/gpiochip''<n>''</tt> device, most likely <tt>/dev/gpiochip5</tt>. You can verify this by running libgpiod's <code>gpioinfo</code> utility, which should now show you an additional GPIO chip with only 8 lines.		Upon booting your board with your modified device tree blob, you should have an additional <tt>/dev/gpiochip''<n>''</tt> device, most likely <tt>/dev/gpiochip5</tt>. You can verify this by running libgpiod's <code>gpioinfo</code> utility, which should now show you an additional GPIO chip with only 8 lines.
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	If you are daisy-chaining the modules, you'll see an additional gpiochip with 8 lines for each additional module.		If you are daisy-chaining the modules, you'll see an additional gpiochip with 8 lines for each additional module.

	=== Testing ~~The Pins As Outputs~~ ===		=== Testing the pins as outputs ===

	To test whether this is working, you can connect an LED between a pin (in this example, 4) of your PCF8574, and ground. Then (assuming your chip number is 5) you can use <code>sudo gpioset -B pull-down 5 4=0</code> to turn off the pin and set its bias mode to be pulled down, and use <code>sudo gpioset 5 4=1</code> to turn it on and <code>sudo gpioset 5 4=0</code> to turn it off. Connecting an LED with no resistor in-line should be fine because the pins deliver like 100mA current at most.		To test whether this is working, you can connect an LED between a pin (in this example, 4) of your PCF8574, and ground. Then (assuming your chip number is 5) you can use <code>sudo gpioset -B pull-down 5 4=0</code> to turn off the pin and set its bias mode to be pulled down, and use <code>sudo gpioset 5 4=1</code> to turn it on and <code>sudo gpioset 5 4=0</code> to turn it off. Connecting an LED with no resistor in-line should be fine because the pins deliver like 100mA current at most.

	=== Programmatically ~~Driving The Pins~~ ===		=== Programmatically driving the pins ===

	'''TODO:''' Expand this section with how to control the pins programmatically using libgpiod or whatever.		'''TODO:''' Expand this section with how to control the pins programmatically using libgpiod or whatever.

	=== Adding ~~A Button To Send A Key Code~~ ===		=== Adding a button to send a key code ===

	In this example, we're adding a button that's hooked between the input pin 0 and ground, and making it type W whenever it's pressed.		In this example, we're adding a button that's hooked between the input pin 0 and ground, and making it type W whenever it's pressed.

CounterPillow: /* Device Tree Changes */ Add info on how to use overlays for this

2023-02-28T14:05:02Z

Device Tree Changes: Add info on how to use overlays for this

@@ Line 10: / Line 10: @@
 To control the chip, you'll need to modify your board's device tree&mdash;a description of its hardware for devices that don't automatically enumerate&mdash;so that the kernel knows how to load the driver.
 {{note|You will need to install <tt>dtc</tt> for this.}}
@@ Line 34: / Line 64: @@
 Now run <code>make dtbs</code> to compile the device tree. This should give you a <tt>arch/arm64/boot/dts/rockchip/rk3566-quartz64-a.dt'''b'''</tt>, which you can then copy into your <tt>/boot/dtbs/</tt> as for example <tt>quartz-with-pcf8574.dtb</tt> or something like that. Then, in your <tt>extlinux.conf</tt>, either add a new boot label or modify your existing boot labels <code>FDT</code> line to point towards this dtb file, with the path being relative to <tt>/boot</tt> and not to <tt>/</tt>.
-=== Daisy Chaining ===
+== Daisy Chaining ==
 As previously stated, you can hook up multiple of these modules onto the same bus. Here's how the device tree changes for this will look like:
@@ Line 60: / Line 90: @@
 '''Note:''' be sure to change the A0, A1 and A2 pins accordingly to set the addresses of the daisy chained modules! For example, for the second module, pull A0 high and leave A1 and A2 low. The address pins work like a binary counter, so 000 -> 001 -> 010 -> 011 -> 100 -> ...
-=== Interrupts ===
+== Interrupts ==
 The PCF8574 will pull its <tt>INT</tt> pin low when one of its inputs changed. We can use this to generate an interrupt:

CounterPillow: Add a new category for guides specific to Quartz64

2021-12-10T11:55:43Z

Add a new category for guides specific to Quartz64

← Older revision		Revision as of 11:55, 10 December 2021
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	Note that you will need to have your PCF8574 set up with interrupts for this.		Note that you will need to have your PCF8574 set up with interrupts for this.

	[[Category:Quartz64]] [[Category:Guide]]		[[Category:Quartz64]] [[Category:Guide]] [[Category:Quartz64 Guides]]

CounterPillow: CounterPillow moved page Using a PCF8574 with a Quartz64 Model A to Quartz64 Model A using a PCF8574

2021-12-07T09:51:20Z

CounterPillow moved page Using a PCF8574 with a Quartz64 Model A to Quartz64 Model A using a PCF8574

← Older revision

Revision as of 09:51, 7 December 2021

CounterPillow: Note about dtc dependency

2021-12-05T11:11:16Z

Note about dtc dependency

← Older revision		Revision as of 11:11, 5 December 2021
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	To control the chip, you'll need to modify your board's device tree—a description of its hardware for devices that don't automatically enumerate—so that the kernel knows how to load the driver.		To control the chip, you'll need to modify your board's device tree—a description of its hardware for devices that don't automatically enumerate—so that the kernel knows how to load the driver.

			{{note\|You will need to install <tt>dtc</tt> for this.}}

	The easiest way to go about this is to get a copy of the Linux kernel source code from https://kernel.org that matches your kernel version (<code>uname -a</code>), as the device tree definitions live in the Linux kernel repository. Technically, device trees should be compatible across kernel versions, but I wouldn't gamble on it.		The easiest way to go about this is to get a copy of the Linux kernel source code from https://kernel.org that matches your kernel version (<code>uname -a</code>), as the device tree definitions live in the Linux kernel repository. Technically, device trees should be compatible across kernel versions, but I wouldn't gamble on it.

CounterPillow: /* Hooking Up The Module */

2021-12-01T12:37:59Z

Hooking Up The Module

← Older revision		Revision as of 12:37, 1 December 2021
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	== Hooking Up The Module ==		== Hooking Up The Module ==

	Hook up SDA to pin number 3 of your board, and SCL to pin number 5. Connect GND to ground, e.g. pin number 9, and VCC to 3.3V, for example pin number 1. If ~~your module has an interrupt~~ pin, you ~~can leave it unconnected for now; producing interrupts when~~ pin ~~states change is an advanced topic we will expand on later~~.		Hook up SDA to pin number 3 of your board, and SCL to pin number 5. Connect GND to ground, e.g. pin number 9, and VCC to 3.3V, for example pin number 1. If you plan on using interrupts, connect the <tt>INT</tt> pin to whichever GPIO you defined as the interrupt pin.

	'''TODO:''' Put photo of hooked up module here.		'''TODO:''' Put photo of hooked up module here.

CounterPillow: interrupts and buttons

2021-12-01T12:27:15Z

interrupts and buttons

@@ Line 57: / Line 57: @@
 '''Note:''' be sure to change the A0, A1 and A2 pins accordingly to set the addresses of the daisy chained modules! For example, for the second module, pull A0 high and leave A1 and A2 low. The address pins work like a binary counter, so 000 -> 001 -> 010 -> 011 -> 100 -> ...
 == Hooking Up The Module ==
@@ Line 79: / Line 102: @@
 If you are daisy-chaining the modules, you'll see an additional gpiochip with 8 lines for each additional module.
 To test whether this is working, you can connect an LED between a pin (in this example, 4) of your PCF8574, and ground. Then (assuming your chip number is 5) you can use <code>sudo gpioset -B pull-down 5 4=0</code> to turn off the pin and set its bias mode to be pulled down, and use <code>sudo gpioset 5 4=1</code> to turn it on and <code>sudo gpioset 5 4=0</code> to turn it off. Connecting an LED with no resistor in-line should be fine because the pins deliver like 100mA current at most.
 '''TODO:''' Expand this section with how to control the pins programmatically using libgpiod or whatever.
 [[Category:Quartz64]] [[Category:Guide]]

CounterPillow: /* Device Tree Changes */ move regs to appropriate place

2021-12-01T09:17:47Z

Device Tree Changes: move regs to appropriate place

← Older revision		Revision as of 09:17, 1 December 2021
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	pcf8574: pcf8574@20 {		pcf8574: pcf8574@20 {
	compatible = "nxp,pcf8574";		compatible = "nxp,pcf8574";
			reg = <0x20>;
	gpio-controller;		gpio-controller;
	#gpio-cells = <2>;		#gpio-cells = <2>;
	~~reg = <0x20>;~~
	};		};
	};		};
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	pcf8574_1: pcf8574@20 {		pcf8574_1: pcf8574@20 {
	compatible = "nxp,pcf8574";		compatible = "nxp,pcf8574";
			reg = <0x20>;
	gpio-controller;		gpio-controller;
	#gpio-cells = <2>;		#gpio-cells = <2>;
	~~reg = <0x20>;~~
	};		};

	pcf8574_2: pcf8574@21 {		pcf8574_2: pcf8574@21 {
	compatible = "nxp,pcf8574";		compatible = "nxp,pcf8574";
			reg = <0x21>;
	gpio-controller;		gpio-controller;
	#gpio-cells = <2>;		#gpio-cells = <2>;
	~~reg = <0x21>;~~
	};		};
	};		};