PTO Micro-Instruction: VMS4 Status Query (pto.get_vms4_sr)

This page documents the PTO micro-instruction runtime query for the VMS4_SR status register. The op is part of the PTO micro-instruction surface (A5 Ascend 950 profile).

Overview

pto.get_vms4_sr exposes the contents of the VMS4_SR hardware register to scalar code. After an exhausted pto.vmrgsort4 merge-sort operation, VMS4_SR records the per-source-list executed counts; reading it lets a kernel reason about how many elements of each input list were consumed.

Mechanism

pto.get_vms4_sr is a pure scalar producer. It does not move data, does not synchronize pipelines, and does not change any architectural state. It simply reads the four 16-bit fields of VMS4_SR and returns them as four SSA i16 values.

The intended pattern is to issue a pto.vmrgsort4 that may exhaust before fully consuming all inputs, then read VMS4_SR to discover how far each source list advanced, and use those counts to drive the next round of sort/merge work.

pto.get_vms4_sr

Syntax: %list0, %list1, %list2, %list3 = pto.get_vms4_sr : i16, i16, i16, i16

Semantics: Read VMS4_SR and return the finished element counts for source lists 0, 1, 2, and 3.

Inputs

None.

Expected Outputs

Result Type Description
%list0 i16 Finished count for source list 0
%list1 i16 Finished count for source list 1
%list2 i16 Finished count for source list 2
%list3 i16 Finished count for source list 3

Register Layout

Bits Meaning
[15:0] finished count for source list 0
[31:16] finished count for source list 1
[47:32] finished count for source list 2
[63:48] finished count for source list 3 
status = VMS4_SR;
list0 = (uint16_t)(status & 0xffff);
list1 = (uint16_t)((status >> 16) & 0xffff);
list2 = (uint16_t)((status >> 32) & 0xffff);
list3 = (uint16_t)((status >> 48) & 0xffff);

Constraints

  • The returned values are unsigned 16-bit counts of elements consumed from each source list.
  • The intended pattern is to read VMS4_SR after an exhausted pto.vmrgsort4 to determine partial-progress counts.
  • The op is a pure scalar producer; it has no architectural side effects.

Examples

// After a partial pto.vmrgsort4, read per-list executed counts
%list0, %list1, %list2, %list3 = pto.get_vms4_sr : i16, i16, i16, i16

// Use the counts to advance the next sort round
%c0_i64 = arith.extui %list0 : i16 to i64
// ... feed back into the next vmrgsort4 setup