[libre-riscv-dev] evaluation of bit-witdh scoreboards
luke.leighton at gmail.com
Mon Dec 17 02:02:37 GMT 2018
More layout thoughts. Will draw diagram tonight.
Reg file divided 32 bit and striped. Dest reg is targetted to go direct
write into regfile, no multiplex, so reg bytes are lined up on source side.
FUs may be grouped together 32-32 to do a 64 bit op, so Reservation
Stations are only 32 bit wide.
Augmented by 8 bit RSs which can do groups 8 8 to do 16 bit ops.
Irony is 64 bit ops only dual issue, 32 bit are quad.
Source routing needs a 2x2 crossbar 32 bit wide for 32 wide FUs.
Then also 8 bit 4x4 crossbars on the 8 bit FUs. Actually 8x8 crossbars
which is a little scary.
Can still do SIMD ops to the 32 bit FUs. 8 bit FUs can do non power 2 cases.
REMAP needs to do 1st by src and then line up with dest. So src ops get
REMAPed by src AND dest map, and dest by dest map.
Otherwise we have to put in src AND dest crossbars and multiplexers.
Can possibly do src-dest REMAP as math shortcut.
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