More info: https://trmm.net/SPI_flash
i: Read chip ID; if all 0xFF or 0x00, then something is wrong.
r7f0000↵: read 16 bytes from 0x7f0000 and hex dump them.
e7f0000↵: erase a sector at address 7f0000.
u190000 1a0000↵: Upload (and erase) 0x1a0000 bytes to 0x190000.
to read the entire rom, shell out and run:
rx < /dev/ttyACM0 > /dev/ttyACM0 rom.bin
Otherwise, please read the source.