Actual CMO Operations

The spreadsheet CMOs.xlsx is a list of some of the desired CMO operation. It is by no means a complete list.

The version uploaded as of 2020-04-30_08.04.31 (TBD: provide link to GitHub version) counts these. These counts suggest the regular format In the next section

Regular format

bits	name	description
1	LG	0=>local, 1=> global
3	scope	e.g. cache level to flush to although sometimes not strictly a level (8 encodings used)
4	cmop	operation type 13 encodings used
1	sec	security related, 0=no, 1=> flush predictors and prefetchers

Scope encodings

we get away with "only" eight encodings, three bits, by overloading - using the same encoding to indicate slightly different things for outboound operations (pulls/flushes) and inbound operations.

for push CMOs	for pull CMOs (prefetchesd)
to pou(I$,D$)	to I$
to pou coherent processor caches	to L1 D$
to pou non-coherent processor caches	to L2$ pou(I,D )
to pou non-coherent I/O	to L3$
to ordinary DRAM	from NVRAM to DRAM
to battery backed up DRAM
to NVRAM ( first point of persistence)
to all NVRAM (full persistence)

we can of course argue about details, to try to reduce the count

• do we need to have two points of NVRAM persistence, first and all?
  • e.g. Keith Packard
  • e.g. HP "Machine" (TBD: ref)
• do we need to distinguish DRAM from battery backed DRAM
  • there are existence proofs, but we don't necessarily need to order them
• do we need to distinguish processor coherence from I/O coherence?
• could I/O coherence be just DRAM

But at the very least, I am sure that most people agree that we need at least four scopes, and probably more. => 3 bits. My biggest concern is that we should probably provide four bits rather than three.

CMO operation encodings

rw	name	detail
r	FLUSH DIRTY --> CLEAN
r	FLUSH DIRTY + CLEAN --> INVALID
w	INVALIDATE	clean --> invalid dirty -- no wb --> invalid
r	INVALIDATE CLEAN	clean --> invalid dirty --> unaffected secure version suitable for NC I/O
r	Set LRU
r	PREFETCH-R	PREFETCH-X has I$ target
r	PREFETCH-W	prefetch to write, may be clean or dirty <
r	? PREFETCH-E	prefetch as if to write, but must be clean may need to update
r	FETCH-W + LOCK	like creating local writable copy of shared RAM
r	FETCH-R + LOCK	like creating local copy of shared ROM
r	FETCH-E + LOCK	like creating private ROM
r	FETCH-EW + LOCK	like creating private RAM

Excel spreadsheet "CMOS.xlsx"

Thursday, April 9, 2020-04-09:

• in GitHub repo at https://github.com/AndyGlew/Ri5-stuff/blob/master/CMOs.xlsx
• (probably has more recent copies elsewhere, e.g. personal machine or cloud Drive) is a "list" of CMOs. Not exactly a list, more like a table from which the actual list can be generated. Many rows of the table can be expanded into several different CMO operations with different privilege requirements, caches affected, etc.

TBD: actually generate a "flat" list. Preferably by script, so that I can automatically go back between the expanded list and a compact form that is folded with common sub expressions that is easier to understand.

Why CMOs.xlsx was written in Excel

OLD, Obsolete

Quick and dirty list of Actual CMOs