intro to #421 Fractional vtype field vfill and #418 vlmt...
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.
No new functionality is proposed for the strawman model.
The definition does allow for a relaxing of SEW size constraints Krste proposed for strawman model.
#413 cluster/decluster instructions: with LMUL<1 loads/stores provide byte/half/word support.
This proposal relies on the strawman model, explained using the CLSTR model, to reformat fractional LMUL data to that of LMUL=1.
In conjunction with load and store byte/half/word to/from double are effected.
(I noted this issue in an email response to the minutes posting, but apparently the message was garbled).
#418 Introduce vlmt (vl multiplicative threshold) / VLMT Vector LiMiT
#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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