openpower/sv/rfc/ls008.mdwn

   1 # RFC ls008 SVP64 Management instructions
   2
   3 [[!tag opf_rfc]]
   4
   5 **URLs**:
   6
   7 * <https://libre-soc.org/openpower/sv/>
   8 * <https://libre-soc.org/openpower/sv/rfc/ls008/>
   9 * <https://bugs.libre-soc.org/show_bug.cgi?id=1040>
  10 * <https://git.openpower.foundation/isa/PowerISA/issues/87>
  11
  12 **Severity**: Major
  13
  14 **Status**: New
  15
  16 **Date**: 24 Mar 2023
  17
  18 **Target**: v3.2B
  19
  20 **Source**: v3.0B
  21
  22 **Books and Section affected**:
  23
  24 ```
  25     Book I, new Scalar Chapter.  (Or, new Book on "Zero-Overhead Loop Subsystem")
  26     Appendix E Power ISA sorted by opcode
  27     Appendix F Power ISA sorted by version
  28     Appendix G Power ISA sorted by Compliancy Subset
  29     Appendix H Power ISA sorted by mnemonic
  30 ```
  31
  32 **Summary**
  33
  34 ```
  35     Instructions added
  36     setvl    - Cray-style "Set Vector Length" instruction
  37     svstep   - Vertical-First Mode explicit Step and Status
  38     svremap  - Re-Mapping of Register Element Offsets
  39     svindex  - General-purpose setting of SHAPEs to be re-mapped
  40     svshape  - Hardware-level setting of SHAPEs for element re-mapping
  41     svshape2 - Hardware-level setting of SHAPEs for element re-mapping (v2)
  42 ```
  43
  44 **Submitter**: Luke Leighton (Libre-SOC)
  45
  46 **Requester**: Libre-SOC
  47
  48 **Impact on processor**:
  49
  50 ```
  51     Addition of six new "Zero-Overhead-Loop-Control" DSP-style Vector-style
  52     Management Instructions which can be implemented extremely efficiently
  53     and effectively by inserting an additional phase between Decode and Issue.
  54     More complex designs are NOT adversely impacted and in fact greatly benefit
  55     whilst still retaining an obvious linear sequential execution programming model.
  56 ```
  57
  58 **Impact on software**:
  59
  60 ```
  61     Requires support for new instructions in assembler, debuggers,
  62     and related tools.
  63 ```
  64
  65 **Keywords**:
  66
  67 ```
  68     Cray Supercomputing, Vectorisation, Zero-Overhead-Loop-Control,
  69     Scalable Vectors, Multi-Issue Out-of-Order, Sequential Programming Model
  70 ```
  71
  72 **Motivation**
  73
  74 TODO
  75
  76 **Notes and Observations**:
  77
  78 1. TODO
  79
  80 **Changes**
  81
  82 Add the following entries to:
  83
  84 * the Appendices of Book I
  85 * Instructions of Book I as a new Section
  86 * SVL-Form of Book I Section 1.6.1.6 and 1.6.2
  87
  88 ----------------
  89
  90 \newpage{}
  91
  92 # svstep: Vertical-First Stepping and status reporting
  93
  94 SVL-Form
  95
  96 * svstep RT,SVi,vf (Rc=0)
  97 * svstep. RT,SVi,vf (Rc=1)
  98
  99 | 0-5|6-10|11.15|16..22| 23-25    | 26-30 |31|   Form   |
 100 |----|----|-----|------|----------|-------|--|--------- |
 101 |PO  | RT | /   | SVi  |  / / vf  | XO    |Rc| SVL-Form |
 102
 103 Pseudo-code:
 104
 105 ```
 106     if SVi[3:4] = 0b11 then
 107         # store subvl, pack and unpack in SVSTATE
 108         SVSTATE[53] <- SVi[5]
 109         SVSTATE[54] <- SVi[6]
 110         RT <- [0]*62 || SVSTATE[53:54]
 111     else
 112         step <- SVSTATE_NEXT(SVi, vf)
 113         RT <- [0]*57 || step
 114
 115 ```
 116
 117 Special Registers Altered:
 118
 119     CR0                     (if Rc=1)
 120
 121
 122 -------------
 123
 124 \newpage{}
 125
 126
 127 # setvl
 128
 129 SVL-Form
 130
 131 * setvl RT,RA,SVi,vf,vs,ms (Rc=0)
 132 * setvl. RT,RA,SVi,vf,vs,ms (Rc=1)
 133
 134 Pseudo-code:
 135
 136     overflow <- 0b0
 137     VLimm <- SVi + 1
 138     # set or get MVL
 139     if ms = 1 then MVL <- VLimm[0:6]
 140     else           MVL <- SVSTATE[0:6]
 141     # set or get VL
 142     if vs = 0                then VL <- SVSTATE[7:13]
 143     else if _RA != 0         then
 144         if (RA) >u 0b1111111 then
 145             VL <- 0b1111111
 146             overflow <- 0b1
 147         else                      VL <- (RA)[57:63]
 148     else if _RT = 0          then VL <- VLimm[0:6]
 149     else if CTR >u 0b1111111 then
 150         VL <- 0b1111111
 151         overflow <- 0b1
 152     else                          VL <- CTR[57:63]
 153     # limit VL to within MVL
 154     if VL >u MVL then
 155         overflow <- 0b1
 156         VL <- MVL
 157     SVSTATE[0:6] <- MVL
 158     SVSTATE[7:13] <- VL
 159     if _RT != 0 then
 160        GPR(_RT) <- [0]*57 || VL
 161     if ((Â¬vs) & Â¬(ms)) = 0 then
 162         # set requested Vertical-First mode, clear persist
 163         SVSTATE[63] <- vf
 164         SVSTATE[62] <- 0b0
 165
 166 Special Registers Altered:
 167
 168     CR0                     (if Rc=1)
 169
 170 -------------
 171
 172 \newpage{}
 173
 174
 175 # SVL-Form
 176
 177 Add the following to Book I, 1.6.1, SVL-Form
 178
 179 ```
 180     |0     |6    |11    |16   |23 |24 |25 |26    |31 |
 181     | PO   |  RT |   RA | SVi |ms |vs |vf |   XO |Rc |
 182     | PO   |  RT | /    | SVi |/  |/  |vf |   XO |Rc |
 183 ```
 184
 185 * Add `SVL` to `RA (11:15)` Field in Book I, 1.6.2
 186 * Add `SVL` to `RT (6:10)` Field in Book I, 1.6.2
 187 * Add `SVL` to `Rc (31)` Field in Book I, 1.6.2
 188 * Add `SVL` to `XO (26:31)` Field in Book I, 1.6.2
 189
 190 Add the following to Book I, 1.6.2
 191
 192 ```
 193     ms (23)
 194         Field used in Simple-V to specify whether MVL (MAXVL in the SVSTATE SPR)
 195         is to be set
 196         Formats: SVL
 197     vf (25)
 198         Field used in Simple-V to specify whether "Vertical" Mode is set
 199         (VF in the SVSTATE SPR)
 200         Formats: SVL
 201     vs (24)
 202         Field used in Simple-V to specify whether VL (in the SVSTATE SPR) is to be set
 203         Formats: SVL
 204     SVi (16:22)
 205          Simple-V immediate field for setting VL or MVL (VL, MAXVL in the SVSTATE SPR)
 206          Formats: SVL
 207 ```
 208
 209
 210 # Appendices
 211
 212     Appendix E Power ISA sorted by opcode
 213     Appendix F Power ISA sorted by version
 214     Appendix G Power ISA sorted by Compliancy Subset
 215     Appendix H Power ISA sorted by mnemonic
 216
 217 | Form | Book | Page | Version | mnemonic | Description |
 218 |------|------|------|---------|----------|-------------|
 219 | SVL  | I    | #    | 3.0B    | svstep   | Vertical-First Stepping and status reporting |
 220