4 ms·

Are there any 128-bit core done yet in FPGA?

• brucehoult 5y ago
  If there's not, it would be less than a day's work to change a few constants in a 64 bit core and add the corresponding equivalents of the same 10 instructions that were added to go from RV32I to RV64I. Fabrice Bellard has had rv128 support in TinyEmu for some years already. If it hadn't been done then it's not because it's in any way difficult (in emulator, FPGA, or SoC) but only that no one has needed it yet.
  • ruslan 5y ago
    Well, I have a doubt that simply increasing bus size to 64 bits you can get working bitstream for FPGAs, even for top notch ones. Something tells me that synthesising/placing/routing such soft-core will face timing and resource limitations. Studying recent ARM based SoCs I usually find that they often use reduced AXI4 buses to 48 or even less bits, making all internal I/O transactions block-wise.
    • brucehoult 5y ago
      Of course you can do it and it will work. A "standard" (e.g. 5 stage pipe in-order) 64 bit RISC-V core takes a very small proportion of even a fairly small FPGA such as an Arty 100T. You can even do multiple cores. 128 bit would fit no problem at all. You'd probably have slightly lower Fmax but there's no question about working and if you actually need 128 bit arithmetic then it will be faster than using multiple instructions on a 64 bit CPU (e.g. 4 instructions for a 128 bit add).