From 4570556215f96cc22cabf18c4430757183d2f6f1 Mon Sep 17 00:00:00 2001 From: Luke Kenneth Casson Leighton Date: Sat, 22 Jun 2019 10:05:52 +0100 Subject: [PATCH] update 64-bit prefix format --- simple_v_extension/sv_prefix_proposal.rst | 118 +++++++++++++++------- 1 file changed, 80 insertions(+), 38 deletions(-) diff --git a/simple_v_extension/sv_prefix_proposal.rst b/simple_v_extension/sv_prefix_proposal.rst index 7a2c6b843..547f90654 100644 --- a/simple_v_extension/sv_prefix_proposal.rst +++ b/simple_v_extension/sv_prefix_proposal.rst @@ -1,4 +1,4 @@ -SimpleV Prefix (SVprefix) Proposal v0.2 +SimpleV Prefix (SVprefix) Proposal v0.3 ======================================= This proposal is designed to be able to operate without SVcsr, but not to @@ -40,8 +40,8 @@ are reused for additional encoding space in the 48-bit instructions. 64-bit Prefixed Instructions ============================ -TODO. Really need to resolve vitp7 by reducing lsk to 2 bits, or just use -0b111111 as the prefix, then lsk can remain at 3 bits. +The 48 bit format is further extended with the full 128-bit range on all source +and destination registers, and the option to set both VL and MVL is provided. 48-bit Instruction Encodings ============================ @@ -123,43 +123,85 @@ Table showing Standard RV32 encodings: 64-bit Instruction Encodings ============================ -TODO (please disregard for now, WIP) - -+--------------+-------+-------+--------+--------+--------+----------+ -| Encoding | 63:58 | 57 | 56 | 55 | 54 | 53:48 | -+--------------+-------+-------+--------+--------+--------+----------+ -| P64-LD-type | VLtyp | rd[6] | rs1[6] | | | MVLtp | -+--------------+-------+-------+--------+--------+--------+----------+ -| P64-ST-type | VLtyp | | rs1[6] | rs2[6] | | MVLtp | -+--------------+-------+-------+--------+--------+--------+----------+ -| P64-R-type | VLtyp | rd[6] | rs1[6] | rs2[6] | | MVLtp | -+--------------+-------+-------+--------+--------+--------+----------+ -| P64-I-type | VLtyp | rd[6] | rs1[6] | | | MVLtp | -+--------------+-------+-------+--------+--------+--------+----------+ -| P64-U-type | VLtyp | rd[6] | | | | MVLtp | -+--------------+-------+-------+--------+--------+--------+----------+ -| P64-FR-type | VLtyp | | rs1[6] | rs2[6] | | MVLtp | -+--------------+-------+-------+--------+--------+--------+----------+ -| P64-FI-type | VLtyp | rd[6] | rs1[6] | rs2[6] | | MVLtp | -+--------------+-------+-------+--------+--------+--------+----------+ -| P64-FR4-type | VLtyp | rd[6] | rs1[6] | rs2[6] | rs3[6] | MVLtp | -+--------------+-------+-------+--------+--------+--------+----------+ - -The extra bit for src and dest registers provides the full range of up to 128 registers, when combined with the extra bit from the 48 bit prefix as well. - -VLtyp - -+--------------+---------+ -| vtyp[5:1] | vtyp[0] | -+--------------+---------+ -| regnum | 1 | -+--------------+---------+ -| immed | 0 | -+--------------+---------+ - -Just as in the VLIW format, when bit 0 of vtyp is zero, bits 1 to 5 specify the scalar register that VL is set from. When bit 0 is 1, VL is set to the immediate (plus one). +Where in the 48 bit format the prefix is "0b0011111" in bits 0 to 6, this is +now set to "0b0111111". + ++---------------+---------------+--------------+-----------| +| 63:48 | 47:18 | 17:7 | 6:0 | ++---------------+---------------+--------------+-----------| +| 64 bit prefix | RV32[31:3] | P48[17:7] | 0b0111111 | ++---------------+---------------+--------------+-----------| + +* The 64 bit prefix format is below +* Bits 18 to 47 contain bits 3 to 31 of a standard RV32 format +* Bits 7 to 17 contain bits 7 through 17 of the P48 format +* Bits 0 to 6 contain the standard RV 64-bit prefix 0b0111111 + +64 bit prefix format: + ++--------------+-------+--------+--------+--------+--------+ +| Encoding | 63 | 62 | 61 | 60 | 59:48 | ++--------------+-------+--------+--------+--------+--------+ +| P64-LD-type | rd[6] | rs1[6] | | | SVtyp | ++--------------+-------+--------+--------+--------+--------+ +| P64-ST-type | | rs1[6] | rs2[6] | | SVtyp | ++--------------+-------+--------+--------+--------+--------+ +| P64-R-type | rd[6] | rs1[6] | rs2[6] | | SVtyp | ++--------------+-------+--------+--------+--------+--------+ +| P64-I-type | rd[6] | rs1[6] | | | SVtyp | ++--------------+-------+--------+--------+--------+--------+ +| P64-U-type | rd[6] | | | | SVtyp | ++--------------+-------+--------+--------+--------+--------+ +| P64-FR-type | | rs1[6] | rs2[6] | | SVtyp | ++--------------+-------+--------+--------+--------+--------+ +| P64-FI-type | rd[6] | rs1[6] | rs2[6] | | SVtyp | ++--------------+-------+--------+--------+--------+--------+ +| P64-FR4-type | rd[6] | rs1[6] | rs2[6] | rs3[6] | SVtyp | ++--------------+-------+--------+--------+--------+--------+ + +The extra bit for src and dest registers provides the full range of +up to 128 registers, when combined with the extra bit from the 48 bit +prefix as well. + +SVtyp field encoding +==================== + ++-----------+-------------+--------------+----------+----------------------+ +| SVtyp[11] | SVtyp[10:6] | SVtyp[5:1] | SVtyp[0] | comment | ++-----------+-------------+--------------+----------+----------------------+ +| 0 | 000000 | 00000 | 0 | no change to VL/MVL | ++-----------+-------------+--------------+----------+----------------------+ +| 0 | VLdest!=0 | 00000 | 0 | reserved | ++-----------+-------------+--------------+----------+----------------------+ +| 0 | VLdest | VLEN | vlt | VL imm/reg mode (vlt)| ++-----------+-------------+--------------+----------+----------------------+ +| 1 | VLdest | MVL+VL-immed | MVL/VL immed mode | ++-----------+-------------+--------------+----------+----------------------+ +Notes: + +* When SVtyp is all zeros, neither VL nor MVL are changed +* SVtype[11]=0, SVtype[5:0]=0 and SVtype[10:6] non-zero is a reserved encoding. + Its uses raises an illegal instruction exception. + +Just as in the VLIW format, when bit 11 of SVtyp is zero: + +* if vlt is zero, bits 1 to 5 specify the VLEN as a 5 bit immediate + (offset by 1: 0b00000 represents VL=1, 0b00001 represents VL=2 etc.) +* if vlt is 1, bits 1 to 5 specify the scalar (RV standard) register + from which VL is set. x0 is not permitted +* VL goes into the scalar register VLdest (if VLdest is not x0) + +When bit 11 of SVtype is 1: + +* both MAXVL and VL are set to (VLenimmed+1) +* the same value goes into the scalar register VLdest (if VLdest is not x0) +This gives the option to set up VL in a "loop mode" (SVtype[11]=0) or +in a "one-off" mode (SVtype[11]=1) which sets both MVL and VL to the +same immediate value. This may be most useful for one-off Vectorised +operations such as LOAD-MULTI / STORE-MULTI, for saving and restoration +of large batches of registers in context-switches or function calls. vs#/vd Fields' Encoding ======================= -- 2.30.2