Oct 17, 2026, 2:35 PM@Mecrisp I would like to have at least 16KB of RAM and Flash, though I guess PSRAM would be fine. I would assume block RAM is most limiting for soft cores?
- Oct 17, 2026, 2:35 PM
Replies
MecrispMecrisp@chaos.socialOct 17, 2026, 4:33 PM@tamme Block RAM often is a limiting factor indeed, but your requirements are absolutely reasonable. The Lattice iCE40 UP5K, for example, comes with 15 kb of initialised block RAM with one read and one write port, 128 kb single port uninitialised RAM which is fine as RAM for a RISC-V softcore, and you can use the space beyond the bitstream in the SPI flash for your own code.
- MecrispMecrisp@chaos.socialOct 17, 2026, 4:34 PM
@tamme It is possible to do execute-in-place directly from the SPI flash for booting and loading your code into the large uninitialised RAM blocks.
All of the Lattice ECP5 chips offer much more.
- MecrispMecrisp@chaos.socialOct 17, 2026, 4:40 PM
@tamme I usually recommend either the Icebreaker or the Radiona ULX3S boards, which both have excellent open source support, and example FemtoRV "phantasy microcontroller" implementations in Mecrisp-Quintus:
https://1bitsquared.de/products/icebreaker
(Lattice UP5K)https://radiona.org/ulx3s/
(Lattice ECP5)Toolchain:
https://github.com/YosysHQ/oss-cad-suite-build/releases/ - Oct 17, 2026, 7:53 PM
@Mecrisp oh cool, maybe I dismissed soft-cores to early. I'll give it a look, the ECP5 seems to be quite powerful and available on boards. Thanks for all the info!