[sdiy] Microcontrollers for eurorack use... What to use?

Chris McDowell declareupdate at gmail.com
Sun Jan 4 03:10:41 CET 2015


Olivier, how would you suggest one get started with the STM32 chips? I’ve always stuck to what I could accomplish within the Arduino IDE, but would really love to “level up”. I bought one of the mbed-enabled nucleo dev boards from ST and really enjoy the extra horsepower, but I don’t want to rely on the mbed environment for developing any actual products. A nudge in the right direction would be much appreciated! :) 



> On Jan 3, 2015, at 7:20 PM, Olivier Gillet <ol.gillet at gmail.com> wrote:
> 
> I've been using the STM32F4s in two modules I have recently announced
> (Elements and Clouds), and have three more down in the pipe. I love
> working with these for the following reasons:
> * Easy to code with, using open-source tools (gcc-arm-none-eabi and
> gdb) and a classic CLI/editor workflow.
> * Relatively easy to interface with an audio codec IC.
> * Code execution from flash is fast (unlike the STM32F1...).
> * 32-bit floating point unit with fused multiply-add, hardware
> division, square root and absolute value.
> * GCC generates very good quality code from C/C++. We're reaping the
> benefits of the popularity of ARM and the collective effort spent on
> compilers...
> * Lots of flash memory.
> * Low power consumption. A complete module (MCU + Codec + op-amps for
> audio and CV conditioning + blinkenlights) for 100mA.
> 
> A few caveats:
> * Small amount of internal SRAM (192kb on STM32F407, 256kb on STM32F427).
> * Internal ADC needs software processing (averaging/low-pass
> filtering) to get decent resolution. Certainly not for audio, OK for
> CVs in the low kHz rate.
> * I2S clock is always 256fs, which can be a problem with some codecs
> to reach some sample rates.
> 
> I haven't tested the external memory interface - the STM32F429 has a
> controller for SDRAM which might be a good option for your looper
> (older parts only support SRAM).
> 
> For synthesis applications, one can get a lot of work done. In my
> modules or through benchmarks, I got them to run:
> * ~100 zero-delay SVF at 48kHz.
> * ~100 basic wavetable oscillators at 48kHz.
> * A 16-band vocoder and several wavetable oscillators at 48kHz (lower
> bands downsampled to 8kHz).
> * 8x 4-op FM voices with oversampling at 96kHz.
> * A mono phase-vocoder with 25% overlapping at 48kHz.
> * Waveshaping/wavefolding/ringmod algorithms at 96kHz with 8x
> oversampling (768kHz).
> * A simple reverb (a dozen APs, 2-3 modulated delays/APs) uses 10% of
> the CPU at 48kHz.
> 
> All of these were from C++ code - but I studied the generated machine
> code carefully and very rarely found inefficiencies.
> 
> On Sun, Jan 4, 2015 at 12:42 AM, Paul Perry <pfperry at melbpc.org.au> wrote:
>> Thanks Scott, that is is line with what a friend said, he had
>> single one taking 200mA (non-music application, but flat out.)
>> 
>> paul perry Melbourne Australia
>> 
>> ----- Original Message ----- From: "Scott Gravenhorst"Subject: Re: [sdiy]
>> Microcontrollers for eurorack use... What to use?
>>> 
>>> I don't have a precise answer for this, however, I've successfully powered
>>> 4 dsPICs (28 pin DIP) from a single 1 ampere 3.3volt supply. three of the
>>> dsPICs were doing audio, one was acting as a MIDI controller talking to two
>>> of the others as voice engines over SPI.
>>> 
>> 
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