The documentation on how to create your own Raspberry Pi CEC debugger was a bit out of date. Update it to the Raspberry Pi 4B, drop the mention of the RTC and a link to a picture that no longer works. Also reorganize the text to make it easier to follow and change the pins to match the pins I use. Signed-off-by: Hans Verkuil <hverkuil-cisco@xxxxxxxxx> --- Added a note that the ground pin of the HDMI connector has to be connected to a ground pin of the RPi. --- diff --git a/Documentation/admin-guide/media/cec.rst b/Documentation/admin-guide/media/cec.rst index 14ec3ff317c2..656dec7e0182 100644 --- a/Documentation/admin-guide/media/cec.rst +++ b/Documentation/admin-guide/media/cec.rst @@ -296,69 +296,71 @@ broadcast messages twice to reduce the chance of them being lost. Specifically Making a CEC debugger ===================== -By using a Raspberry Pi 2B/3/4 and some cheap components you can make +By using a Raspberry Pi 4B and some cheap components you can make your own low-level CEC debugger. -Here is a picture of my setup: - -https://hverkuil.home.xs4all.nl/rpi3-cec.jpg - -It's a Raspberry Pi 3 together with a breadboard and some breadboard wires: - -http://www.dx.com/p/diy-40p-male-to-female-male-to-male-female-to-female-dupont-line-wire-3pcs-356089#.WYLOOXWGN7I - -Finally on of these HDMI female-female passthrough connectors (full soldering type 1): +The critical component is one of these HDMI female-female passthrough connectors +(full soldering type 1): https://elabbay.myshopify.com/collections/camera/products/hdmi-af-af-v1a-hdmi-type-a-female-to-hdmi-type-a-female-pass-through-adapter-breakout-board?variant=45533926147 -We've tested this and it works up to 4kp30 (297 MHz). The quality is not high -enough to pass-through 4kp60 (594 MHz). - -I also added an RTC and a breakout shield: +The video quality is variable and certainly not enough to pass-through 4kp60 +(594 MHz) video. You might be able to support 4kp30, but more likely you will +be limited to 1080p60 (148.5 MHz). But for CEC testing that is fine. -https://www.amazon.com/Makerfire%C2%AE-Raspberry-Module-DS1307-Battery/dp/B00ZOXWHK4 +You need a breadboard and some breadboard wires: -https://www.dx.com/p/raspberry-pi-gpio-expansion-board-breadboard-easy-multiplexing-board-one-to-three-with-screw-for-raspberry-pi-2-3-b-b-2729992.html#.YGRCG0MzZ7I - -These two are not needed but they make life a bit easier. +http://www.dx.com/p/diy-40p-male-to-female-male-to-male-female-to-female-dupont-line-wire-3pcs-356089#.WYLOOXWGN7I -If you want to monitor the HPD line as well, then you need one of these -level shifters: +If you want to monitor the HPD and/or 5V lines as well, then you need one of +these 5V to 3.3V level shifters: https://www.adafruit.com/product/757 (This is just where I got these components, there are many other places you can get similar things). +The ground pin of the HDMI connector needs to be connected to a ground +pin of the Raspberry Pi, of course. + The CEC pin of the HDMI connector needs to be connected to these pins: -CE0/IO8 and CE1/IO7 (pull-up GPIOs). The (optional) HPD pin of the HDMI -connector should be connected (via a level shifter to convert the 5V -to 3.3V) to these pins: IO17 and IO27. The (optional) 5V pin of the HDMI -connector should be connected (via a level shifter) to these pins: IO22 -and IO24. Monitoring the HPD an 5V lines is not necessary, but it is helpful. +GPIO 6 and GPIO 7. The optional HPD pin of the HDMI connector should +be connected via the level shifter to these pins: GPIO 23 and GPIO 12. +The optional 5V pin of the HDMI connector should be connected via the +level shifter to these pins: GPIO 25 and GPIO 22. Monitoring the HPD and +5V lines is not necessary, but it is helpful. + +This device tree addition in ``arch/arm/boot/dts/bcm2711-rpi-4-b.dts`` +will hook up the cec-gpio driver correctly:: -This kernel patch will hook up the cec-gpio driver correctly to -e.g. ``arch/arm/boot/dts/bcm2837-rpi-3-b-plus.dts``:: + cec@6 { + compatible = "cec-gpio"; + cec-gpios = <&gpio 6 (GPIO_ACTIVE_HIGH|GPIO_OPEN_DRAIN)>; + hpd-gpios = <&gpio 23 GPIO_ACTIVE_HIGH>; + v5-gpios = <&gpio 25 GPIO_ACTIVE_HIGH>; + }; cec@7 { compatible = "cec-gpio"; cec-gpios = <&gpio 7 (GPIO_ACTIVE_HIGH|GPIO_OPEN_DRAIN)>; - hpd-gpios = <&gpio 17 GPIO_ACTIVE_HIGH>; + hpd-gpios = <&gpio 12 GPIO_ACTIVE_HIGH>; v5-gpios = <&gpio 22 GPIO_ACTIVE_HIGH>; }; - cec@8 { - compatible = "cec-gpio"; - cec-gpios = <&gpio 8 (GPIO_ACTIVE_HIGH|GPIO_OPEN_DRAIN)>; - hpd-gpios = <&gpio 27 GPIO_ACTIVE_HIGH>; - v5-gpios = <&gpio 24 GPIO_ACTIVE_HIGH>; - }; +If you haven't hooked up the HPD and/or 5V lines, then just delete those +lines. This dts change will enable two cec GPIO devices: I typically use one to send/receive CEC commands and the other to monitor. If you monitor using an unconfigured CEC adapter then it will use GPIO interrupts which makes monitoring very accurate. +If you just want to monitor traffic, then a single instance is sufficient. +The minimum configuration is one HDMI female-female passthrough connector +and two female-female breadboard wires: one for connecting the HDMI ground +pin to a ground pin on the Raspberry Pi, and the other to connect the HDMI +CEC pin to GPIO 6 on the Raspberry Pi. + The documentation on how to use the error injection is here: :ref:`cec_pin_error_inj`. ``cec-ctl --monitor-pin`` will do low-level CEC bus sniffing and analysis.
