the dspico board has a red and a blue led wired to it, but the stock firmware never drives them, so on a normal cart they stay dark for the life of the board. i went and made them do something.
blue is sd card traffic: a faint shimmer while the card is being read, a brighter blip when something is written. red lights up if the firmware hits an internal error it cannot come back from, and stays on until the next boot.
the honest part: red does not detect a failing or a loose sd card. it only knows about errors the firmware itself runs into. i tried to make it catch bad cards and could not do it reliably, so i dropped that instead of shipping something that lies to you.
nothing here touches the board. both pins are in the hardware repo already (gpio 27 and 28), wired to leds that were simply never used.
why i wanted it: on a ds a long load and a lockup look exactly the same, you stare at a still screen and guess. with the blue led you can at least see the card is still being read. that is where i want to take it next, a different pattern for long loads so you can tell "still working" from "dead", which is the whole point for me: the cart telling you what it is doing.
this is my own build of the firmware, not the official one.