However if your application is not going to be controlling the brakes or steering then limiting yourself to things that can be programmed in Arduino IDE is not too difficult.
I'm not going to control any of main safety devices in car, only cutting ignition 
By "automotive" MCU I meant that they are recomended by manufacturer, because they comply with AEC-Q100.
As You can see on Microchip website:
ATSAMD21E15 - recommended for automotive designs,
ATSAMD21E15L - not a word about recomemdation for automotive.
I'm going to sell that product, thats why I'm worried about compliance etc.
DVDdoug:
What are you measuring?
The ATmega chip can run from an internal oscillator, but I don't know if you'll get less elecomagnetic noise. And compared to an ignition system on motor???
I'm measuring readings from in-amp which reads strain gauge bridge. That's why every bit counts for me. Range is 0-3.3V, then I can't go for 1.1V.
When it comes to emited EMC noise I've read that internal oscilator generates less noise than external, then I'd like to throw away external and run only off internal one.
Right now I have 5V regulator on board and then 3.3V for OLED display, and it would be best solution if i can throw away 5V regulator and run with only 3.3V, but doesn't atmega328p have problems with running on 3.3V and internal clock? That's why I'm looking at SAMD21.
Here, in Poland I can't get teensy 3.2 chips, since I don't want to use boards, just chips...
alesam:
Chinese guys created an “improved” clone of Atmega 328 - LGT8F328P
It has 12bit ADC, can run witgout cristall on 32MHz, has extra timer, no fuses, embedded DAC etc. But otherwise compatible.
Datasheet (google translated) - https://www.electrodragon.com/w/images/b/b6/LGT8F88P_LGT8F168P_LGT8F328P_translated.pdf
You can by an “arduino” board - https://raliexpress.com/item/KEYES-LGT8F328P-UNO/32967207992.html
This board has the same MCU - https://ru.aliexpress.com/item/WAVGAT-Pro-ATMEGA328P-328-ATMEGA328-5-16-arduino-Nano-Micro/32954774902.html
One more board - LILYGO? TTGO XI 8F328P-U Development Board For Nano V3.0 Promini Or Replace Sale - Banggood USA sold out-arrival notice-arrival notice
Hmm... chinese chip... I'm a bit worried about compliance with any directive...