Graham Sutherland / PolynomialMay 26, 2024

SD cards are the literal worst.

they've expanded to be the size of small hard drives, and devices like the rpi keep using them as boot media, but they:

- use garbage tier low endurance flash cells internally
- have little to no overprovisioning for wear
- perform only the most basic wear levelling
- have no protocol level integrity checking
- have few internal error correction features, if any
- decay comparatively quickly without patrol scrubs
- do not perform patrol scrubs
- cannot do PLP

Show threadGraham Sutherland / PolynomialMay 26, 2024
I've been mad about this pretty much forever. Don't use SD cards for stuff where there's literally any other option.
Show threadGraham Sutherland / PolynomialMay 26, 2024

something I've been thinking about a lot is engineering panic signals into embedded stuff.

put a rail supervisor on the incoming supply, and leave enough capacitance on the low side of your buck(-boost) reg to keep the device running for a few milliseconds when the power is pulled. treat the supervisor IC's PG output as a panic signal and have it trigger an IO interrupt on your MCU/SoC which tells the filesystem code to ensure integrity, flush, and halt IO.

Show threadPeter BindelsMay 26, 2024
@gsuberland Why low side? High side seems better wrt brownout detection.
Show threadGraham Sutherland / Polynomial
@dascandy rail supervisor on incoming supply is high side?
May 26, 2024 at 6:10pmWeb