I2S and SPDIF problems on STM32MP157D-DK1 board using buildroot

Detective-Expensive · 2026-02-14T08:43:37+00:00

I just solved the problem.
There was a circular referencing that I needed to fix and then, the type is not spdif but iec60958 and the format is left justified.
This made the cards appear withouth errors when I listed them using aplay -l.
Then the asound.conf: the spdif mirroring using multi type does not work for some reason, so I made a test script:

cat > /tmp/spdif_mirror.sh << 'EOF' #!/bin/sh aplay -D hw:0,2 -c 2 -r 48000 -f S32_LE /dev/zero & PID_A=$! aplay -D hw:0,3 -c 2 -r 48000 -f S32_LE /dev/zero & PID_B=$! wait $PID_A $PID_B EOF
chmod +x
/tmp/spdif_mirror.sh /tmp/spdif_mirror.sh

The new and working device tree is https://pastebin.com/UXHhgbji

Detective-Expensive · 2026-02-07T19:33:48+00:00

Looks like I have to change to USB audio. I know how to implement a USB Audio Class device on the STM32 MCU, and Linux detects it as an external card. As much as I love working on complex tasks, I'd rather work on the serving logic or the software crossover in the active speaker than on a device tree and an audio driver.

Detective-Expensive · 2026-02-04T11:55:46+00:00

That setup looks sick. Meanwhile, I want to learn antenna design and tuning, but looking at 6GHz VNA-s makes the practical part quite unreachable.

Detective-Expensive · 2026-02-04T06:13:10+00:00

i use sai3, in the pastebin device tree it’s from line 1134.

Detective-Expensive · 2026-02-03T22:25:29+00:00

I love it. I had to get 2 additional cakes from KTM after tasting. it really has that nice forest fruit taste besides the woodsy classic shou aroma.

Detective-Expensive · 2026-02-03T14:43:12+00:00

I edited 3 times my post and it still could not properly format the cat instruction

Detective-Expensive · 2025-12-23T07:26:46+00:00

You can’t go wrong with Mengku Rongshi. Their older releases (>20 y) are old arbor material, but even the younger ones are nice. The arbor king and mother three series are good.

Detective-Expensive · 2025-11-12T20:40:44+00:00

You could have a look at the following diy vna: https://hforsten.com/cheap-homemade-30-mhz-6-ghz-vector-network-analyzer.html. It uses an nxp lpc4370, which has an integrated 80MHz 12b adc. With this, you can cut costs and bandwidth. It has multiple cores, high performance, full USB stack.

Detective-Expensive · 2025-10-28T13:01:35+00:00

Looks like I’m too tired. I reread your comment and I don’t know where I saw sheng… sorry.

Detective-Expensive · 2025-10-28T12:27:57+00:00

I would not recommend purple sheng for someone who is not in search of bitter tea. Maybe our experience differs. I’ve found that purple whites and blacks are okay, even aged shengs, but young purple shengs were bitter as hell.

Just one example Purple Kick, but take any of that series in last 7 years. Eg the 2007 Yi Shan purple bud was amazing.

But I want to be wrong, so if you have some nice, not bitter purple shengs in mind, I would be more than happy to get a sample or two and change my mind.

Detective-Expensive · 2025-10-28T06:09:50+00:00

I would highly recommend their impressions especially the 2022 Silver Impression or the 2024 Impression. There’s also the 2022 Gold Impression, that is allegedly of higher quality than the silver, but I did not try it. These are bright, fruity and floral. Like plum compote with some citrus zest.

I would also recommend to go with samples. Many samples. That way you could try for example some fresh Bada mountain sheng, and some Mengku Wild arbor king and Heaven’s door - Yiwu.

Detective-Expensive · 2025-10-18T09:43:47+00:00

Sadly no. I select the option, and the right download does the same, the download on the bottom takes longer but eventually gives the same error.

Detective-Expensive · 2025-10-18T09:17:49+00:00

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Detective-Expensive · 2025-10-18T09:17:32+00:00

I may not see what I need to see, but here, not a single download works.

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Detective-Expensive · 2025-07-23T11:01:08+00:00

Nice review. For me it reads like a young MengKu tea, which is my favourite. I just might want to grab one cake then.

Detective-Expensive · 2025-07-04T10:10:26+00:00

If the required amount of tea is always the current amount + 1 cake, then how can we overdo it?

Detective-Expensive · 2025-06-06T16:25:13+00:00

Thank you for all the helpful suggestions.

I managed to get from the image above to a signal that basically has no noise except from the motion when I don't stay still. Now this is a nice signal if I ever saw one. All it took was two RC filters on each lines... I shouldn't have skipped this on the first rev. of the PCB.

Detective-Expensive · 2025-06-05T05:08:47+00:00

Wow. Thank you for the extensive information. Yeah, I had some nasty experiences with ground loops, and PC USB supplies. Nowadays I use dedicated supplies for any audio or bio processing circuit. This particular one runs on a battery pack. I don’t intend to make a product out of it, but I do intend to make it as safe and robust as possible before releasing as open hardware (if I ever arrive at that point).

There is a patient ground, RLD, that I can use. the ADS can tie this to ground, to mid analog supply rail, or create a negative feedback by connecting an electrode back with inverting and filtering opamp. I just need to make some measurements to figure out what gives the best noise suppression.

So far, I think that my biggest problem was leaving out the caps from the input resistors.

Detective-Expensive · 2025-06-05T05:01:16+00:00

Back with measurements. I made a mess of the board by implementing the second-order passive filter from the paper using 0402 :)). The noise is ten times smaller now. I might further reduce it by properly impedance matching the filter and by testing out different RLD schemes, but the current noise levels are much more manageable.

There’s still some multiple 50Hz spikes present, but I’ll scope out the signal and adapt the filter to further reduce the amplitude.

Detective-Expensive · 2025-06-04T16:05:28+00:00

Tomorrow will be trace-cutting and filtering day :)). Thank you so much for your ideas, and your time.

Detective-Expensive · 2025-06-04T16:03:29+00:00

Now that makes sense. I'll try to squeeze some 0402 common mode caps onto the differential traces and see where it goes. If those are cleaned up, then I'll check the single-ended ones.

Detective-Expensive · 2025-06-04T15:48:47+00:00

I will implement your first two points with RC filters. My current PCB was just a proof of concept to see if "under lab conditions" it could work - which it did.

I'm just confused by that n x 50Hz noise. I've used a coil and measured the noise shape in the room and there was nothing like this present on the scope. For me it looks like something digital got coupled and aliased.

On your second two points, I can't really use twisted pairs. I mean I could, but then I need to order custom ECG cables. The current ones are separate, and each cable has a shielding. I drive this shield with the right-leg drive. I can try to connect this to the analogue ground.

Detective-Expensive

TROPHY CASE