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by oweno
Tue Apr 30, 2019 1:08 pm
Forum: Compute Module
Topic: Compute Module Stock Levels / Production Schedule
Replies: 3
Views: 505

Compute Module Stock Levels / Production Schedule

The compute module (CM3+/Lite) is currently out of stock everywhere...

Newark is reporting availability on 9/23/19

That is a long lead time!

Is there any news about production schedule for these modules?
by oweno
Mon Dec 03, 2018 2:41 am
Forum: Compute Module
Topic: Disabling Activity LED (after enabling it)
Replies: 2
Views: 1203

Re: Disabling Activity LED (after enabling it)

Thanks for this! It seems to work fine after a quick check.
by oweno
Sun Dec 02, 2018 12:39 pm
Forum: Compute Module
Topic: Disabling Activity LED (after enabling it)
Replies: 2
Views: 1203

Disabling Activity LED (after enabling it)

In our application we have a status LED connected to GPIO 24 and configured as the activity led : dtoverlay=pi3-act-led,gpio=24,activelow=on This works great, but is there a way to disable activity led on this pin after boot up? Essentially I want to alert the user of activity during boot up, then o...
by oweno
Sat Sep 29, 2018 1:18 am
Forum: Compute Module
Topic: I2C Problems on SDA
Replies: 42
Views: 5153

Re: I2C Problems on SDA

I think I've mentioned crosstalk. There are some more issues with your PCB which should be changed if you make a new revision. There are some vias which are useless, and your VCC traces should be re-routed, as well as better decoupling (placemenf of caps). Yes, thank you for the input! definitely s...
by oweno
Wed Sep 26, 2018 7:51 pm
Forum: Compute Module
Topic: I2C Problems on SDA
Replies: 42
Views: 5153

Re: I2C Problems on SDA

OK.... so finally realized the I2C errors happen when the I2S interface gets turned on. The WM8731 is configured as I2S master so it is spitting out bit clock, LR clock, and data out back to the CM. These 3 traces run parallel and right next to the I2C lines SDA and SCL for about 2 cm. There are ter...
by oweno
Tue Sep 25, 2018 7:11 pm
Forum: Compute Module
Topic: I2C Problems on SDA
Replies: 42
Views: 5153

Re: I2C Problems on SDA

Whats the bandwidth of your Scope / Probe (is the Probe in x10 mode) - first confirm your not B/W limited on your scope (does it have a Calibrator Output for probe compensation)? I can confirm the scope is not BW limited. ...so probes were in 1x mode. When I switch to 10x, I no longer see those spi...
by oweno
Tue Sep 25, 2018 7:02 pm
Forum: Compute Module
Topic: I2C Problems on SDA
Replies: 42
Views: 5153

Re: I2C Problems on SDA

Have you tested with a different device/target already? If there is a problem coming from your PCB (i.e. crosstalk issue) you will never figure out this way. If you know your I2C code is working reliable you can re-connect the codec. Or check with another board which has the codec mounted. Sure, I'...
by oweno
Tue Sep 25, 2018 1:00 pm
Forum: Compute Module
Topic: I2C Problems on SDA
Replies: 42
Views: 5153

Re: I2C Problems on SDA

at the second image that he posted, the rise time was give a take 1-2us. And that value is at the high side for a I2C bus. Yes, I was thinking about that. certainly seems borderline, and this might help explain why performance improves when pull up R is reduced (faster rise times). But it is not th...
by oweno
Mon Sep 24, 2018 6:07 pm
Forum: Compute Module
Topic: I2C Problems on SDA
Replies: 42
Views: 5153

Re: I2C Problems on SDA

Your adding extra capacitance to the SDA line by leaving it attached - which suggest either troublesome ringing - or a timing issue as your delaying the SDA in relation to the SCL by adding the extra capacitance of the probe I thought (hoped) it was a timing thing too, and it would make sense that ...
by oweno
Mon Sep 24, 2018 5:41 pm
Forum: Compute Module
Topic: I2C Problems on SDA
Replies: 42
Views: 5153

Re: I2C Problems on SDA

What Kind of probes are you using? How big is their capacitive load? They are just regular 1m passive bnc scope probes, so I guess capacitance is around 100pF... Maybe you should use a logic analyzer for further debugging of your communication. I have one and it is what led me to discovering all th...
by oweno
Mon Sep 24, 2018 2:57 am
Forum: Compute Module
Topic: I2C Problems on SDA
Replies: 42
Views: 5153

Re: I2C Problems on SDA

If we are lucky added a couple of 100nF directly across Pin 1 - Pin 28 and Pin 27 - Pin 28 will resolve the problem ... fingers crossed Sadly this didn't change the situation :( But thanks for pointing it out, I'll definitely fix those caps on the next board! Another observation: if I remove the sc...
by oweno
Sun Sep 23, 2018 2:42 pm
Forum: Compute Module
Topic: I2C Problems on SDA
Replies: 42
Views: 5153

Re: I2C Problems on SDA

Than we can see why the voltage is not 0V. And this is well good by the clk. The picture where data line (SDA) doesn't go to 0V is the result of using a small value pull-up, and is normal. I was only trying to illustrate what the signal looked like during the ACK phase. clock line (SCL) still has t...
by oweno
Sat Sep 22, 2018 6:12 pm
Forum: Compute Module
Topic: I2C Problems on SDA
Replies: 42
Views: 5153

Re: I2C Problems on SDA

Cirrus Logic now Co. owns one of my Patents when they bought out Wolfson... Interesting about Cirrus Logic, what was your patent for? I double checked all the power pins were connected early on, wishing it was something like that. But I'm glad you mentioned about PSU decoupling. There is a 100nF ca...
by oweno
Sat Sep 22, 2018 2:57 pm
Forum: Compute Module
Topic: I2C Problems on SDA
Replies: 42
Views: 5153

Re: I2C Problems on SDA

Reading the Wolfson Datasheet and the 2 Wire interface is described as a 2-wire MPU serial interface with NO mention of I2C so I would suspect I2C 'like' but not necessarily 100% I2C compatible I was wondering about this. But it might also be a licensing thing. Might be a clue here in this control ...
by oweno
Sat Sep 22, 2018 2:49 pm
Forum: Compute Module
Topic: I2C Problems on SDA
Replies: 42
Views: 5153

Re: I2C Problems on SDA

Do you have another I2C device available, i.e an EEPROM? Good point, should try another I2C device, although I have tried multiple boards / parts, so I'm pretty sure it is not a problem with specific part or CM. Also I get same result from both WM8731 and TLV320AIC23B, pin compatible devices from d...
by oweno
Fri Sep 21, 2018 6:16 pm
Forum: Compute Module
Topic: I2C Problems on SDA
Replies: 42
Views: 5153

Re: I2C Problems on SDA

Brandon92 wrote:Maybe a picture of your test setup?
Here are 2 photos of test setup, with and without probes attached. The bottom board has the WM8731 audio codec. It also has socket for Compute Module, but wanted to take that out of the equation, so driving the board with the standard CMIO board.
by oweno
Fri Sep 21, 2018 6:09 pm
Forum: Compute Module
Topic: I2C Problems on SDA
Replies: 42
Views: 5153

Re: I2C Problems on SDA

Without 220 Ohm resistor.
by oweno
Fri Sep 21, 2018 6:07 pm
Forum: Compute Module
Topic: I2C Problems on SDA
Replies: 42
Views: 5153

Re: I2C Problems on SDA

Sure, that looks like this. (see next post, sorry having trouble with these images!)
by oweno
Fri Sep 21, 2018 6:02 pm
Forum: Compute Module
Topic: I2C Problems on SDA
Replies: 42
Views: 5153

Re: I2C Problems on SDA

It really does look like some kind of pull-up is being released one clock period prior to the successful ACK. When I reduce pull-up resistor on SDA to 700 Ohm and use a 200 Ohm series resistor like this: http://www.thepeacetreaty.org/diagram.JPG I am able to take the following picture during a succ...
by oweno
Fri Sep 21, 2018 2:53 pm
Forum: Compute Module
Topic: I2C Problems on SDA
Replies: 42
Views: 5153

Re: I2C Problems on SDA

Thanks for this info. Removing pull-ups I can still see some activity on SDA and SCL, but not really spikes. I thought I read that GPIO 2 and 3 have weak internal (50k?) pull-ups, and what I see is in line with that, very slow rise times that do not make thresholds. So I don't know if it is an activ...
by oweno
Thu Sep 20, 2018 6:29 pm
Forum: Compute Module
Topic: I2C Problems on SDA
Replies: 42
Views: 5153

Re: I2C Problems on SDA

series resistors, Rs in this pic.

Rp = 4k7
Rs = 220 Ohm
by oweno
Thu Sep 20, 2018 4:38 pm
Forum: Compute Module
Topic: I2C Problems on SDA
Replies: 42
Views: 5153

I2C Problems on SDA

Asking this question here, still not certain if this is a CM / RPI issue or not. I thought it might be a problem with the I2C device itself (in this case an audio codec). But I've observed the behavior on 2 different slave device: the TLV320AIC23B and the compatible WM8731. I'm debugging a single I2...
by oweno
Wed Sep 19, 2018 5:31 pm
Forum: Compute Module
Topic: WM8731 Audio Codec, I2C weirdness
Replies: 6
Views: 1866

Re: WM8731 Audio Codec, I2C weirdness

Placing 220 Ohm series resistors on SDA and SCL right before the WM8731 eliminates the NAKs. I am willing to accept this solution and move on, but I also don't understand why they should be necessary. Seems the WM8731 is especially sensitive to grounding or signal integrity or something. Perhaps no ...
by oweno
Fri Sep 14, 2018 8:21 pm
Forum: Compute Module
Topic: WM8731 Audio Codec, I2C weirdness
Replies: 6
Views: 1866

Re: WM8731 Audio Codec, I2C weirdness

Yeah, definitely some electrical issues. Lowering pull-ups help, but something going on with our boards I think. One strange observation is when I have scope probes connected to the I2C lines it causes tons more NAKs. I have separate logic analyzer attached and might see a few NAK, then attaching os...
by oweno
Fri Sep 14, 2018 4:21 pm
Forum: Compute Module
Topic: Eagle files for Compute Module
Replies: 2
Views: 1863

Re: Eagle files for Compute Module

Here is a basic layout in Eagle for the CM3 I just put up. It is based on the CMIO board and uses many of the same parts. I think the only one I changed was the tiny BGA TVS diodes on the HDMI port to a part that was a little larger.

https://github.com/owenosborn/CM3-Basic-PCB

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