| Version 1 (modified by trac, 6 years ago) (diff) |
|---|
GCN 1.2 VOP_SDWA and VOP_DPP encodings
The GCN 1.2 architecture provides two new VOP encoding enhancements which adds new features. The VOP_SDWA adds possibility to choosing and interesting bytes, words in operands. The VOP_DPP adds new parallel features to manipulating wavefronts (moving data between threads).
VOP_SDWA
The VOP_SDWA encoding is enabled by setting 0xf9 in VSRC0 field in VOP1/VOP2/VOPC encoding. List of fields:
| Bits | Name | Description |
|---|---|---|
| 0-7 | SRC0 | First source vector operand |
| 8-10 | DST_SEL | Destination selection |
| 11-12 | DST_UNUSED | Format for unused bits |
| 13 | CLAMP | CLAMP modifier |
| 16-18 | SRC0_SEL | Source data selection for SRC0 |
| 19 | SRC0_SEXT | Signed extension for SRC0 |
| 20 | SRC0_NEG | Negation modifier for SRC0 |
| 21 | SRC0_ABS | Absolute value for SRC0 |
| 24-26 | SRC0_SEL | Source data selectio for SRC1 |
| 27 | SRC1_SEXT | Signed extension for SRC1 |
| 28 | SRC1_NEG | Negation modifier for SRC1 |
| 29 | SRC1_ABS | Absolute value for SRC1 |
The DST_SEL modifier determines which first part of destination dword will be placed
to choosen part with same length of this dword.
This make operation (RESULT & PARTMASK) << PARTSHIFT.
The SRC0_SEL and SRC1_SEL determines what part of source dword will be placed to first
part of this source dword. This make operation (SOURCE>>PARTSHIFT) & PARTMASK.
Possible part selection for DST_SEL, SRC0_SEL and SRC1_SEL:
| Value | Name | CLRX names | Description |
|---|---|---|---|
| 0 | SDWA_BYTE_0 | BYTE0, BYTE_0, B0 | Byte 0 of dword |
| 1 | SDWA_BYTE_1 | BYTE1, BYTE_1, B1 | Byte 1 of dword |
| 2 | SDWA_BYTE_2 | BYTE2, BYTE_2, B2 | Byte 2 of dword |
| 3 | SDWA_BYTE_3 | BYTE3, BYTE_3, B3 | Byte 3 of dword |
| 4 | SDWA_WORD_0 | WORD0, WORD_0, W0 | Word 0 of dword |
| 5 | SDWA_WORD_1 | WORD1, WORD_1, W1 | Word 1 of dword |
| 6 | SDWA_DWORD | DWORD, DW | Whole dword |
The DST_UNUSED modifier specify how to fill bits that do not hold by choosen part. Following options:
| Value | Name | CLRX name | Descrption |
|---|---|---|---|
| 0 | SDWA_UNUSED_PAD | PAD | Fill by zeroes |
| 1 | SDWA_UNUSED_SEXT | SEXT | Fill by last bit of parts (sign), zero pad lower bits |
| 2 | SDWA_UNUSED_PRESERVE | PRESERVE | Preserve unused bits |
The modifier SEXT (applied by using sext(operand)) apply sign extension
(fill bits after part) to source operand while for source operand was not
selected whole dword (SDWA_DWORD not choosen).
