Getting started with Pi TV HAT and gpio-ir

Hi all,

Much of this message would probably belong to some wiki page, along with 
some photographs that I made. Before starting to write this, I checked 
https://vdr-projects.github.io and did not find any hardware projects.  
The hardware section of the VDR wiki at https://www.linuxtv.org does not 
seem to have been updated for years; it does not mention Raspberry Pi at 
all, despite it being a viable alternative for more than 10 years.

I was an active VDR user from 2004 or 2005, when I built a PC based 
setup, using a "budget" DVB-T card (Hauppauge Nova-T PCI). That system 
was never upgraded to DVB-T2; instead, we got a flat screen TV with a 
built-in tuner. Gradually, as our children got older, recordings were 
made and watched less often.

We mostly stopped using VDR about 10 years ago. Since then, I have made 
some attempts to "come back", initially, using a Raspberry Pi 2 B and an 
Astrometa USB DVB-T/T2 stick.

This month, I purchased a TV HAT case and the DVB-T/T2 uHAT for my 
Raspberry Pi 2 B. As far as I understand, the plexiglass TV HAT case 
should fit the Raspberry Pi 2, 3, and 4. The LED holes next to the 
MicroSD card slot are on the wrong side for the Pi 2, but everything 
fits perfectly.

I regret that I did not buy the Pi TV HAT earlier. The USB stick is 
simply garbage compared to it.

The Astrometa USB stick switches channels very slowly and the tuner very 
frequently produces errors in the bit stream, when using a good outdoor 
aerial that other devices have no trouble with. By design, its infrared 
receiver will lose messages when a button is being held down, because a 
128-byte buffer of the microcontroller would overflow, and there is no 
way to use it as a ring buffer (I tried). A kernel maintainer came up 
with some experimental patches that significantly improved the 
situation, but every few of seconds some key-repeat events were still 
being lost.

Out of that effort, a tiny patch from me was included in the Linux 
kernel, to have the kernel's LIRC interface set the "repeat" flag for 
all IR protocols: 
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=b464763cc3489af406437a7650de8575a0973235

The Pi TV HAT is missing an infrared receiver out of the box. I soldered 
an IR receiver module to some thin wires, isolating the legs with heat 
shrink tube. The other ends of the thin wires I soldered to some pads 
next to the connector: 3.3V at pin 1, ground at pin 6 (or 9), and the 
signal output to GPIO 18 (pin 12). GPIO 17 at pin 11 would have worked 
as well. I made the IR receiver module stick out from a vent hole on the 
top, because my initial attempt of keeping the module inside the 
transparent lid of the case did not work that well.

The module can pick up IR signal some 8 meters away.

The software configuration was easy:

(1) Add the following line to /boot/config.txt:

dtoverlay=gpio-ir,gpio_pin=18

(2) Execute "sudo apt install ir-keytable"

(3) Edit /etc/rc_maps.cfg to load a suitable table for your remote 
control unit. To reuse the old remote control unit that I had, I wrote 
an entry
* * hauppauge.toml

(4) Reboot for the config.txt change to take effect.

For me, the remote control unit appeared in /dev/input/event0 as well as 
/dev/lirc0 and some buttons (such as the number keys) would directly 
work in the /dev/tty1 textual login prompt.

For starting up VDR, I used a command like this:

vdr -v /var/lib/vdr/video --no-kbd -Prpihddevice -P'remote -i /dev/input/event0'

Yes, the Pi TV HAT was detected automatically; I did not have to do 
anything special. I had previously used the same VDR configuration with 
an Astrometa USB stick.

This is with a copy of https://github.com/reufer/rpihddevice with some 
critical patches applied. (The issues and a pull request that I opened 
in January 2022 are still unattended.)

The experience with the Pi TV HAT is simply great. The Sony tuner in the 
Pi TV HAT produces an error-free bit stream and switches transponders 
very quickly. The kernel GPIO IR driver is rock solid. I think that the 
user experience is at least as good as with my old PC setup.

Some buttons on my remote control unit were unreliable. Using an expired 
debit card, I was able to pry open the grey Hauppauge remote control 
unit, starting next to the IR LED. I guess I should upload pictures of 
the internals somewhere, to help others open theirs.

Next, I plan to attach some external storage for recordings. A USB 3.0 
NVMe drive would allow faster backups (when detached from the Raspberry 
Pi 2) and an upgrade to a Pi 3 or 4.

On the software side, I am thinking to apply my kernel patch and to 
write a "kernel LIRC plugin" for VDR that would allow me to use 
/dev/lirc0 for the input. I would prefer to use the lower-level 
interface where each IR message corresponds to an event. I do not like 
the key-repeat timer logic of the kernel's input event driver. And I 
never liked the user-space lircd.

With best regards,

	Marko

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