From: Luke Kenneth Casson Leighton Date: Thu, 29 Sep 2022 11:30:09 +0000 (+0100) Subject: mention idea of reserving 25% only of PO9 for non-Vectorised uses X-Git-Tag: opf_rfc_ls005_v1~266 X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=ca2167376faee1e2d6288c7faa667334a6519d96;p=libreriscv.git mention idea of reserving 25% only of PO9 for non-Vectorised uses --- diff --git a/openpower/sv/rfc/ls001.mdwn b/openpower/sv/rfc/ls001.mdwn index 48c63be09..15c0fd29c 100644 --- a/openpower/sv/rfc/ls001.mdwn +++ b/openpower/sv/rfc/ls001.mdwn @@ -820,12 +820,10 @@ and reserved areas, QTY 1of 32-bit, and QTY 3of 55-bit, are: | 0-5 | 6 | 7 | 8-31 | 32-3 | Description | |-----|---|---|-------|------|---------------------------| -| PO9?| 1 | 0 | 0000 | xx | `RESERVED1` or EXT300-363 | -| PO9?| 0 | x | xxxx | 0b00 | `RESERVED2` or EXT200-216 | -| PO9?| 0 | x | xxxx | 0b01 | `RESERVED2` or EXT216-231 | -| PO9?| 0 | x | xxxx | 0b10 | `RESERVED2` or EXT232-247 | - -Where: +| PO9?| 1 | 0 | 0000 | xx | `RESERVED1` or EXT300-363 (32-bit) | +| PO9?| 0 | x | xxxx | 0b00 | `RESERVED2` or EXT200-216 (55-bit) | +| PO9?| 0 | x | xxxx | 0b01 | `RESERVED2` or EXT216-231 (55-bit) | +| PO9?| 0 | x | xxxx | 0b10 | `RESERVED2` or EXT232-247 (55-bit) | * SVP64Single (`RESERVED3/4`) is *planned* for a future RFC (but needs reserving as part of this RFC) @@ -851,9 +849,21 @@ Bit-allocation Summary: * QTY 3of 55-bit spaces also exist for future use (longer by 3 bits than opcodes allocated in EXT001) * Simple-V EXT2nn is restricted to range EXT248-263 -* non-Simple-V EXT2nn (if ever allocated by a future RFC) is restricted to range EXT200-247 +* non-Simple-V (non-Vectoriseable) EXT2nn (if ever requested in any future RFC) is restricted to range EXT200-247 * Simple-V EXT0nn takes up 50% of PO9 for this and future Simple-V RFCs +**This however potentially puts SVP64 under pressure (in 5-10 years).** +Ideas being discussed already include adding LD/ST-with-Shift and variant +Shift-Immediate operations that require large quantity of Primary Opcodes. +To ensure that there is room in future, +it may be better to allocate 25% to `RESERVED`: + +| 0-5 | 6 | 7 | 8-31 | 32 | Description | +|-----|---|---|-------|-----|---------------------------| +| PO9?| 1 | 0 | 0000 | x | EXT300-363 or `RESERVED1` (32-bit) | +| PO9?| 0 | x | xxxx | 0b0 | EXT200-232 or `RESERVED2` (56-bit) | +| PO9?| 0 | x | xxxx | 0b1 | EXT232-263 and SVP64(/V/S) | + The clear separation between Simple-V and non-Simple-V stops conflict in future RFCs, both of which get plenty of space. EXT000-063 pressure is reduced in both Vectoriseable and