From 3474bdb5d8c70f5ccc081a4f61db736e56680de0 Mon Sep 17 00:00:00 2001 From: lkcl Date: Tue, 20 Jul 2021 11:10:04 +0100 Subject: [PATCH] --- openpower/sv/sprs.mdwn | 24 +++++++++++++++++++++++- 1 file changed, 23 insertions(+), 1 deletion(-) diff --git a/openpower/sv/sprs.mdwn b/openpower/sv/sprs.mdwn index 515dc99f9..39c82df3c 100644 --- a/openpower/sv/sprs.mdwn +++ b/openpower/sv/sprs.mdwn @@ -67,6 +67,27 @@ full context save/restore (see SVSRR0). It contains (and permits setting of): * SUBVL * svstep - the subvector element offset of the current parallel instruction being executed +* vfirst - Vertical First mode. srcstep, dststep and substep + **do not advance** unless explicitly requested to do so with + pseudo-op svstep (a mode of setvl) +* hphint - Horizontal Parallelism Hint. In Vertical First Mode + hardware **MAY** perform up to this many elements in parallel + per instruction. Set to zero to indicate "no hint". + +For hphint, the number chosen must be consistently +executed **every time**. Hardware is not permitted to execute five +computations for one instruction then three on the next. +hphint is a hint from the compiler to hardware that up to this +many elements may be safely executed in parallel. +Interestingly, when hphint is set equal to VL, it is in effect +as if Vertical First mode were not set, because the hardware is +given the option to run through all elements in an instruction. +This is exactly what Horizontal-First is: a for-loop from 0 to VL-1 +except that the hardware may *choose* the number of elements. + +*Note to programmers: changing VL during the middle of such modes +should be done only with due care and respect for the fact that SVSTATE +has exactly the same peer-level status as a Program Counter.* The format of the SVSTATE SPR is as follows: @@ -84,7 +105,8 @@ The format of the SVSTATE SPR is as follows: | 38:39 | mo0 | REMAP RT SVSHAPE0-3 | | 40:41 | mo1 | REMAP EA SVSHAPE0-3 | | 42:46 | SVme | REMAP enable (RA-RT) | -| 47:61 | rsvd | reserved | +| 47:t4 | rsvd | reserved | +| 55:61 | hphint | horizontal parallelism hint | | 62 | RMpst | REMAP persistence | | 63 | vfirst | Vertical First mode | -- 2.30.2