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media: admin-guide/media/cec.rst: update CEC debugging doc 

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bit out of date.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@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>
This commit is contained in:
Hans Verkuil 2023-02-15 12:01:51 +01:00 committed by Mauro Carvalho Chehab
parent 5a84798e03
commit 3e59c24006
1 changed files with 37 additions and 35 deletions
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72
Documentation/admin-guide/media/cec.rst
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@ -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).
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.
I also added an RTC and a breakout shield:
You need a breadboard and some breadboard wires:
https://www.amazon.com/Makerfire%C2%AE-Raspberry-Module-DS1307-Battery/dp/B00ZOXWHK4
http://www.dx.com/p/diy-40p-male-to-female-male-to-male-female-to-female-dupont-line-wire-3pcs-356089#.WYLOOXWGN7I
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.
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 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.
The ground pin of the HDMI connector needs to be connected to a ground
pin of the Raspberry Pi, of course.
This kernel patch will hook up the cec-gpio driver correctly to
e.g. ``arch/arm/boot/dts/bcm2837-rpi-3-b-plus.dts``::
The CEC pin of the HDMI connector needs to be connected to these pins:
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::
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.