The RP2040 is new microcontroller from Raspberry Pi that features
two Cortex M0s and eight PIO state machines that are good for
crunching lots of data. It has 264k RAM and a built in UF2
bootloader too.
Datasheet: https://pico.raspberrypi.org/files/rp2040_datasheet.pdf
1. Make _extext and _sidata coincide. Old _etext location did not include
.ARM.exidx sections, which were usually absent but not always. So flash
data was copied to RAM in wrong place.
2. Use decimal constants with "K" and "M" suffixes in .ld files instead
of hex constants, to make them easier to read and check for accuracy.