il_diavolo
Posts: 164
Joined: Mon Dec 02, 2013 7:56 pm

Screen and RPi B Rev 2

Thu Nov 12, 2015 10:42 pm

Tonight I finally found some spare time to try out the I2C work around to enable the screen with my Pi B rev 2. I updated and upgraded the Rasbian ("Wheezy") on the SD card, connected the jumper leads (2 no.) to the SDA and SDL pins on both the display and the Pi, powered the screen and the Pi from separate power supplies, added ignore_lcd=0 to /boot/config.txt, connected the ribbon cable to the DSI connector (checking carefully it was the correct way round), rebooted ----- and nothing.

I could connect headless to the Pi B so I know that it had booted. I swapped the ribbon cable and the Pi power supply to my Pi 2 to confirm that the display was working, it was.

Obviously I have made an error somewhere in the above, or does the work around only work with Jessie? If anyone has any ideas I'd be most grateful.

By the way, I made some new legs for my Pimoroni frame from some 15mm wide strips of aluminium bent into L shapes to cope with the upside down screen, simples!

il_diavolo
Posts: 164
Joined: Mon Dec 02, 2013 7:56 pm

Re: Screen and RPi B Rev 2

Fri Nov 13, 2015 12:49 pm

Thinking about it (my post above) I probably haven't set up the I2C in raspi-config. I'll try that this evening.

il_diavolo
Posts: 164
Joined: Mon Dec 02, 2013 7:56 pm

Re: Screen and RPi B Rev 2

Fri Nov 13, 2015 8:23 pm

Enabled IC2, although I was pretty sure I'd previously done it. Still no response from the screen. I tried powering the Pi from the display board via the GPIO pins as set out in the article. The Pi powers up so I know the display board is "live" (although that's pretty obvious as it works on my Pi 2). As far as I can ascertain I have carried out every step of the procedure, but to no avail.

Has anybody else managed to get this to work? Presumably they did in Pi Towers, hence the work around on the web site.

6by9
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
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Location: ZZ9 Plural Z Alpha, aka just outside Cambridge.

Re: Screen and RPi B Rev 2

Fri Nov 13, 2015 9:38 pm

Which procedure exactly were you following - you don't say. The official display docs are at https://www.raspberrypi.org/documentati ... /Readme.md
Please note:
NB: With the display connected to the GPIO I2C pins, the GPU will assume control of the respective I2C bus. The host operating system should not access this I2C bus as simultaneous use of the bus by both the GPU and Linux will result in sporadic crashes.
ie do NOT enable I2C access from raspi-config, as that is enabling I2C from Linux.

The display is supported by the firmware blob, not the distribution (ie Jessie vs Wheezy). You can check the firmware version with

Code: Select all

vcgencmd version
You need a release from Oct 21 later to get the correct handling for the DSI display on A/B. "sudo rpi-update" to get the latest.

SDA should be connected to GPIO2, which is pin 3 on the header. SCL should be connected to GPIO3, which is pin 5. If you have enabled i2c-1 under Linux, i2c-detect -y 1 should report 2 active I2C addresses - that should be possible even with the ribbon cable disconnected (as long as there is a GND line connected somewhere). Don't forget to disable I2C access again before really trying to use the touchscreen.

I'd also suggest you connect the HDMI - if the DSI screen fails to respond, then the Pi will drop back to HDMI, so it's blatantly obvious if things have worked or not.
Software Engineer at Raspberry Pi Ltd. Views expressed are still personal views.
I'm not interested in doing contracts for bespoke functionality - please don't ask.

il_diavolo
Posts: 164
Joined: Mon Dec 02, 2013 7:56 pm

Re: Screen and RPi B Rev 2

Fri Nov 13, 2015 11:03 pm

Thanks 6by9.
Which procedure exactly were you following - you don't say. The official display docs are at https://www.raspberrypi.org/documentati ... /Readme.md
That was the link I was following. It looks as though the problem may be that I perhaps had previously enabled IC2 on the particular SD card that I was using (I've got dozens of 'em). Forgive my ignorance, but to disable IC2 do I just use raspi-config again and select the disable option?
I'm afraid, my ignorance again, that I didn't connect the enabling action in raspi-config with enabling it in Linux, now I know better.
I'll give things another try following your suggested steps.
Thanks again.

il_diavolo
Posts: 164
Joined: Mon Dec 02, 2013 7:56 pm

Re: Screen and RPi B Rev 2

Sat Nov 14, 2015 11:46 am

OK, or rather not OK.
sudo rpi-update carried out.
Rebooted (several times)
i2c disabled (in raspi-config)
All connections checked, rechecked and re-rechecked.
Nothing.
Connected HDMI and it's "blatantly obvious" that the 7" display is not being detected.

A couple of things from your post, "vcgencmd version" spawns a long hex number which means nothing to me (sorry, I'm trying to understand, honestly!)

ic2-detect -y 1 gives the result -- "command not found". Should that happen?

I know I can solve this problem by purchasing another Rpi 2 (one that's not built into a robot, like my mine) but that seems too easy. I haven't yet tried soldering wires to physically connect the I2C lines to the DSI connector as demonstrated by Ait in a previous thread, my soldering skills are more plumbing than electronics.

Colin

ait
Posts: 128
Joined: Sun Oct 30, 2011 6:51 pm

Re: Screen and RPi B Rev 2

Sat Nov 14, 2015 4:06 pm

Hello Colin ,
i tried it on both Raspi B ver. 1 + 2 (not that ones i soldered lines on) with Raspbian Jessie.
It works on both of them.

I did
rpi update
ignore_lcd=0 in /boot/config.txt
raspi-config ->Advanced Options -> I2C --> Would you like the ARM I2C interface to be enabled? -> NO
reboot

and it worked.

Ait

il_diavolo
Posts: 164
Joined: Mon Dec 02, 2013 7:56 pm

Re: Screen and RPi B Rev 2

Sun Nov 15, 2015 7:13 pm

Great news, I finally got it to work!
Not sure what I had wrong as I didn't change anything, it just worked the next time I plugged up. I suspect that I hadn't pushed one of the jumper leads fully onto the pins, despite many checks.
Thanks for your help.
Colin

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