An FPGA optimized tiny processor core for embedded systems. See more documentation on the github.io website for Leros.
This repository contains two versions of Leros: the initial 16-bit version in VHDL and the redesign of 16/32/64-bit version in Chisel. The two versions are in the same spirit, but not compatible. The initial version exposes the pipeline to the programmer. The initial version is supported by a small Java runtime (muvium).
The new version is pipeline agnostic and also has a slightly different ISA. The new version is supported by a C compiler (LLVM port.)
- Is load immediate sign extending? Is the high form sign extending?
- Yes, it is. Needs tests and documentation.
- What else is sign extending?
- byte order:
- Morten's simulator (and presumable compiler) is little-endian
- Martin's ISA simulator is little-endian (not yet)
- Patmos is probably big-endian
- Internet is big-endian
- RISC-V is little-endian
Pipeline discussion:
- Maybe decoding and sign extension into fetch
- Play around with the pipeline registers when (1) more complete ALU and (2) longer programs (= block RAM)
- Several different pipeline organizations might be interesting
We target a very high fmax in an FPGA to compensate for the more instructions execute.
Initial measurement on DE2-115 with almost no function and debug output (e.g., accu) in registers: 184 MHz. Could be better.