[Resolved] Attaching PCM5102 to Omega2 (I2S)

  • @sza2-sza2 Wow! Terrific news!!

    Thanks a lot for the nice diagrams (Saleae Logic is great ;-)

    Did you apply all of my patches, in particular, did you apply 942-omega2-dma-bughunt-WIP?

    Because since that patch, I can use aplay without crash, and I even see the WS clock running during the time a sound plays, but there is zero output on the data line. So I thought that something is wrong in the DMA setup, such that no data reaches the i2s engine. But if it works in your case, it can't be a fundamental DMA problem. Maybe something as mundane as a short on my PCB… (I'll re-check that, although needs some time to disassemble the pixelboard)

    BTW: what is the SHA of the LEDE (git rev-parse HEAD) you've been using?

  • @luz Hi,

    Actually, I did not apply all the patches. I modified some files manually as the patching was failed (probably the delta was to big to successfully apply - I did not spend so much time to figure out why).

    I cloned the repo first last week commit 78057457912170ceba29792ef02ba441abe8f246 and I did a lot of tinkering, I don't remember the several config changes I made.

    So yesterday I cloned again (cb2a3911e15df3be15126fc17fabe6f3671eee7b) to have a fresh copy and I did the following:

    1. added MAX98357A related stuff to target/linux/ramips/modules.mk (based on your patch)
    2. added target/linux/ramips/patches-4.4/0722-asoc-enable-max98357a-kconfig.patch
      (well, I'm not a kernel guru, so I don't understand why it is necessary to replace tristate with tristate "Maxim MAX98357A CODEC" in Kconfig but the compilation stopped with errors if I did not apply this)
    3. added lines to OMEGA2.dtsi based on your patches (my current OMEGA2.dtsi) - modifications in mt7628an.dtsi was not necessary

    The result of the above was a kernel which supports MAX98357A (thus PCM5102 too).

    Hope this helps.


    PS: I like Saleae - however I ran into trouble due to its limitation that no continuous sampling to disk, but the maximum is the free RAM size. Although the support was good, they offer a full refund of price of the two Logic Pro 16 - well, we chose not to send back but use for other tasks :-)

  • @sza2-sza2 it works now!! :-D

    Thanks a lot for the detailed steps!

    I was using lede-17.01 before, which is still on kernel 4.4 and had the problem with DMA that made it either crash or (with my attempt to fix it with 942-omega2-dma-bughunt-WIP) not transfer data to the output.

    Apparently, some work and bugfixes for the mt76xx SoCs got upstreamed into Linux mainline between 4.4 and 4.9. At least, the DMA related LEDE patch target/linux/generic/patches-4.4/132-mips_inline_dma_ops.patch that contains the code which was causing the crash, has disappeared in LEDE master.

    Anyway - i2s sound output with max98357a works now, with less patching than before! Great!

    But no advance without new problems - with kernel 4.9 the PWM support (/sys/class/pwm/)… does not work any more, because it tries and fails to claim gpio18 for some unknown reason, which is already claimed by something else, for another unknown reason ;-)

  • @luz Hi,

    Glad to hear that I2S works - bad, that something else broken :-( Currently, I don't plan to use any PWM stuff - but as a newbie I still struggling even with simple GPIOs (it works with official v0.1.9-b159 - so I'm almost sure it is a kernel configuration difference or some user space mistake I made).


  • Hi @luz & @sza2-sza2 have you already tested the quality of sound through i2s on Omega? How is it? Is it worth the fort of compiling custom fw, or it is better to use simple USB-SoundCards?
    Can someone of you please share fw image with working i2s for omega2 or omega2p?

  • @Xplatforms I haven't really tested it, because in my application it's for game sounds (more beeping than music) and connected to a very tiny loudspeaker of limited quality.

    But I see no reason why the sound should be inferior to USB soundcards. i2s as such is lossless, it only depends on the output chip and its specs. I am using the MAX98357A, a really tiny (3x3mm housing) class D mono amplifier chip designed for phone and tablet speakers, and I'd say my setup sounds like a phone.

    On the contrary, USB sound is much more complicated and probably also needs more CPU time from the Omega2.

  • @luz I'm asking because of that comment from onion admins: 0_1502276838089_omega.png
    in this topic: https://community.onion.io/topic/287/solved-i2s-pins-on-omega/5

    Can you share your image for test purpose please?

  • @Xplatforms said in [Resolved] Attaching PCM5102 to Omega2 (I2S):

    @luz I'm asking because of that comment from onion admins: 0_1502276838089_omega.png
    in this topic: https://community.onion.io/topic/287/solved-i2s-pins-on-omega/5

    I see. No idea why Boken came to that conclusion - but then, that was two years ago with the Omega1/AR9331. Could well be that ASoC (ALSA for SoCs) wasn't ready back then. After all, ASoC for the MT7688 started working apparently only with a kernel newer than 4.4.

    Can you share your image for test purpose please?

    The image is highly customized for the application (the "pixelboard" - tetris/game-of-life lounge table)), so it might be a bit difficult to use, but here's the image where aplay works via MAX98357A. You might need to enter "failsafe" mode and edit out the "*" in /etc/shadow for the root user to be able to login.

  • @Xplatforms Hi,

    First of all, I not an audiophile guy. Although my experience with the DAC mentioned in the topic title is pretty good - at least to my ears. You can also take a look at the sine wave I captured, there's no distortion, no noticeable noise on it, that's a quite good waveform.

    I've tested the channels by a 20W class-D amplifier (TPA3100 based), and it was good too. Obviously, the analog part is sensitive to the digital noise generated by the Omega2.

    Regarding the USB sound cards, there are huge differences between specific models. Years ago, I bought one for ~2USD but its sound is terrible (I've tested it with the same Omega2 HW a few month ago - that's why I decided to find some way to use the I2S DAC).

    On the other hand, I heard the sound of a so called Hi-Fi USB sound card and that was rather like my I2S HW (I cannot decide whether it was better or worse, but about the same quality).

    I cannot say anything about the resource side, I assume @luz is right.


  • @luz , @sza2-sza2 thank you very much for your answers and sharing image! I'll try it today

  • @luz I think the gpio18 is used for the max98357a at the dts file,

    sdmode-gpios = <&gpio0 18 GPIO_ACTIVE_HIGH>;

    you can remove that pin config, and try.

Log in to reply

Looks like your connection to Onion Community was lost, please wait while we try to reconnect.