intro to #421 Fractional vtype field vfill and #418 vlmt...
David Horner
Previous issues I opened on fractional LMUL were exploratory, suggesting various ways to encode and enable the feature.
The latest 4 issues opened on github are specific proposals based on the strawman recommendation Krste made on March 24th. These are complimentary proposals which can be implemented individually or collectively. #411 CLSTR and clstr: width specifiers for data cluster in each SLEN chunk. (when LMUL<=1/2) Defines the user visible machine specific fractional LMUL characteristics. #421 Fractional vtype field vfill – Fractional Fill order and Fractional Instruction eLement Location This proposal enables more modes of operation over the strawman model. It reduces to LMUL>=1 when vfill=00 and to the strawman model when vfill=01. The additional modes (vfill=10 and vfil=11) allow for 1) doubling the capacity of fractional registers (and register groups if #418 is also enacted) 2) processing pairs of clustered elements in tandem. 3) allow a single physical register to source the data for widening operations in the common case LMUL=1/2. I realize everyone is busy with various aspects of the standard and that not everyone subscribes to github riscv-v-spec, so I wanted to send out his overview prior to tomorrows meeting. |
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