I recently started using the ESP32 and its IDF sdk, and find it hits all the authors’s desiderata.
I'm still impressed with the wifi functionality. It's a cool chip, and I appreciate the company's willingness to support hobbiests. I wouldn't use their SDK as the reference for a particularly good vendor support package, though. On the other hand, maybe there are no good vendor support packages and ESP32 is one of the least worst?
Overall I'd say it's not too bad, or not so much worse than other chips. It seems every piece of embedded hardware will have quirks and the SDK's will have pain points. From what I gather and my limited experience, it's more a matter of how many and how severe. I prefer at least an open source SDK where it's possible to share patches with the broader community. From what I gather here and elsewhere the only other open source SDK's are for the Nordic chips.
P.S. the esp32's ADC supposedly has terrible calibration issues.
When using software triggered ADC conversions via an 8Khz timer interrupt, the racey issue would occur periodically for several milliseconds at a time. The ADC would act as if its input was disconnected and floating. With a changing input signal, the samples would read as a nearly constant voltage and completely miss blips that were well within the Nyquist frequency.
Switching to I2S/DMA seemed to work around that issue. Even with the ADC working reliably, the samples suffer from what I can only guess is horrendous differential non-linearity. The waveform really looks quite ugly, despite the ADC being driven by a very low impedance amplifier output. At least I can clean up the ECG plots with a low pass filter to make them pretty. The pacemaker pulse is a 350uS square wave, but the heart's natural impulses are significantly lower frequency.
Oh I've read about the ESP32 ADC being pretty non-linear, but the racey issues are new to me. Do you have example code/repo for how you use the I2S to read the ADC? I'd like to add it to my ESP32 wrapper library (see `elcritch/Nesper` on GitHub)). It's mostly started as Nim wrapper's for the ESP-IDF api's, but it is letting me wrap certain errors conditions in the ESP-IDF and configure workarounds. Mostly small stuff, but handy.
Here's the relevant section. I was getting pretty fed up with battling the ESP32, so it's probably not the prettiest.
http://sgtnoodle.com/files/adc_snippet.txt
The function runs as an RTOS task, woken up once every millisecond by a timer. I also pinned it to one of the two CPUs because I was originally doing software triggered sampling at 8Khz. The timer and pinning is rather overkill since I2S clocks the sampling and has tons of buffer.
In an effort to get better data, I have the I2S sample at 40Khz. The function copies the samples out the I2S buffers, and down-samples to 8Khz. The 8Kz samples are pushed into a circular buffer that uses a std::atomic head pointer to make it thread safex.