The main RP2350 changes:
* Two Arm Cortex-M33F, instead of Cortex-M0+
* Two RISC-V "Hazard3" cores (which share the bus with the Arm cores, so you can't have all four)
* 520 KiB of SRAM, up from 264 KiB
* It comes in QFN60 (A) or QFN80 (B) packages. Sorry, it's not pin compatible - I'm told it needed extra ground pins
* Zero (RP2350x) or 2 MiB (RP2354x) of on-chip flash
* It supports QSPI PSRAM as well as QSPI Flash, and there's two Chip Select lines
* It starts at $0.80
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