> Ingenuity runs Linux (for the first time on Mars) and uses the open-source F' software framework on a 2.26 GHz quad-core Snapdragon 801 processor. Radiation hardened processors aren’t fast enough for the real-time vision requirements of the experiment—but as an unprotected COTS processor, it will fail periodically due to radiation-induced bit flips, possibly as much as every few minutes. NASA’s solution is to use a radiation-tolerant FPGA ProASIC3 to keep an eye on the CPU (paper) and software that attempts to double-check operations as much as possible. “[I]f any difference is detected they simply reboot. Ingenuity will start to fall out of the sky, but it can go through a full reboot and come back online in a few hundred milliseconds to continue flying.”
I would be interested in seeing what they did to get Linux booting and their userspace daemon running in ~300ms or less. Depending on their non-volatile storage read rate, using an uncompressed kernel might not actually save boot time. I'm guessing they aren't running traditional init or systemd.
I've been told LinuxBIOS is able to get you a text console login prompt faster than hdd platters can spin up, but it takes Ubuntu tens of seconds on my SSD laptop to get me a login prompt.
I'm surprised they don't have an FPGA MEMS autopilot with a simple degree 2 or 3 polynomial model of the flight dynamics , with the CPU and Linux only being involved in making adjustments to the autopilot. Or, maybe that's what they're doing, and by "falling out of the sky" what they really mean is the autopilot drifting.
