[sdiy] Electrosmith Eurorack DSP platform

Mike Bryant mbryant at futurehorizons.com
Thu Jan 27 12:16:52 CET 2022

Don't even think of using the RP2040 to digitise or generate audio.   The ADCs are rubbish and they've now downgraded the spec to something like 8.9 bits.  They just say some of the capacitors are the wrong value, but I wonder if they made the usual beginners mistake of calculating the capacitance between two metal layers, but not the capacitance to the rest of the chip.

It does have a lot of PWMs but they are all true PWMs and don't have the PDM mode one usually sees (with the counter lines to the comparator swapped around) for generating reasonable quality audio.

As for the SDK, it's just basic setting functions.  There are quite a few examples of how to use it for some things like the I2C master, but no I2C slave.
The USB just borrows the whole TinyUSB which doesn't support MIDI hosts, and has limitations in other host modes.  Okay for making a HID device though.
Also the SPI interface on the chip is borked - it won't even communicate with the larger Raspberry Pis !.

The one nice thing it has is the two PIOs which I think they did obviously spend a lot of time on.  These allow you to roll your own interfaces and I've implemented a 120Mbps drop and insert ring network using them.  It would be great to see these on future STM32s.

Another bad thing is the clocking.  Everything is synced to the crystal.  You can replace this with an external sourced clock, but it's impossible to handle situations where you need two independent clocks, such as USB and studioclock or SPDIF in.

So in the end it's a hobbyist's chip, but at the moment it's one of the few games in town.  How they managed to secure enough slots at TSMC I've no idea, but they can supply MCUs and STM & NXP can't.

-----Original Message-----
From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of cheater cheater via Synth-diy
Sent: 27 January 2022 09:52
To: Eric Brombaugh
Cc: synth-diy at synth-diy.org
Subject: Re: [sdiy] Electrosmith Eurorack DSP platform

On Thu, Jan 27, 2022 at 1:33 AM Eric Brombaugh via Synth-diy <synth-diy at synth-diy.org> wrote:
> I've done one port to RP2040 so far and migrating is definitely a 
> shock to the system. A few things I've noticed:
> * The SDK libraries cover a lot of basic stuff you'd want to do, but 
> not everything that STM32 HAL does. Be prepared to "roll your own".

Could you give some examples please?

> * The RP2040 ADC is a lot noisier than anything on STM32. They claim 
> 12-bits resolution and 10-bit accuracy. Expect less unless you're 
> doing a lot of integration.

How is the RP2040 as a massive amount of audio DACs?

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