From: Luke Kenneth Casson Leighton Date: Sat, 29 Dec 2018 02:22:55 +0000 (+0000) Subject: add notes X-Git-Tag: convert-csv-opcode-to-binary~4764 X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=eda1549b06bbf8502d9b38f1ac92964dee709ab3;p=libreriscv.git add notes --- diff --git a/3d_gpu/microarchitecture.mdwn b/3d_gpu/microarchitecture.mdwn index e68fc9c18..126dd1646 100644 --- a/3d_gpu/microarchitecture.mdwn +++ b/3d_gpu/microarchitecture.mdwn @@ -397,7 +397,7 @@ arithmetic these days. ---- -> however... we don't mind that, as the vectorisation engine will +> however... we don't mind that, as the vectorisation engine will > be, for the most part, generating sequentially-increasing index > dest *and* src registers, so we kinda get away with it. @@ -417,7 +417,7 @@ Read as much as you need in 4 cycles for another operand, read as much as you need in 4 cycles for the last operand, then write as much as you can for the result. This simply requires flip-flops to capture the width and then deliver operands in parallel (serial to parallel converter) and -similarly for writing. +similarly for writing. ---- @@ -436,6 +436,28 @@ also, discussion of how to have multiple instructions issued even with the same dest reg: drop the reg-store and effectively rename them to "R.FU#". exceptions under discussion. +# Register File having same-cycle "forwarding" + +discussion about CDC 6600 Register File: it was capable of forwarding +operands being written out to "reads", *in the same cycle*. this +effectively turns the Reg File *into* a "Forwarding Bus". + +we aim to only have (4 banks of) 2R1W ported register files, +with *additional* Forwarding Multiplexers (which look exactly +like multi-port regfile gate logic). + +suggestion by Mitch is to have a "demon" on the front of the regfile, +, +which: + + basically, you are going to end up with a "demon" at the RF and when + all read reservations have been satisfied the demon determines if the + result needs to be written to the RF or discarded. The demon sees + the instruction issue process, the branch resolutions, and the FU + exceptions, and keeps track of whether the result needs to be written. + It then forwards the result from the FU and clears the slot, then writes + the result to the RF if needed. + # Design Layout ok,so continuing some thoughts-in-order notes: