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Make rvpy cycle-accurate enough to get the correct Dhrystone score

This commit is contained in:
Luke Wren 2022-06-09 01:34:37 +01:00
parent 11596a5bd7
commit d31b1708db
1 changed files with 26 additions and 2 deletions
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28
test/sim/rvpy/rvpy
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@ -1,6 +1,6 @@
#!/usr/bin/env python3
# Minimal RISC-V interpreter, supporting RV32I + Zcsr only, with trace disassembly
# Minimal RISC-V interpreter, RV32IM + Zicsr only, with trace disassembly
import argparse
import sys
@ -160,8 +160,9 @@ class RVCore:
self.mem = mem
self.pc = reset_vector
self.csr = RVCSR()
self.stage3_result = None
def step(self, instr=None, log=True):
def step(self, instr=None, log=True, cycle_accurate=True):
if instr is None:
instr = self.mem.mem[self.pc >> 2]
regnum_rs1 = instr >> 15 & 0x1f
@ -174,6 +175,8 @@ class RVCore:
pc_wdata = None
log_disasm = None
instr_invalid = False
stall_cycles = 0
stage3_result_next = None
opc = instr >> 2 & 0x1f
funct3 = instr >> 12 & 0x7
@ -239,6 +242,7 @@ class RVCore:
if funct3 != 0b000:
mul_result >>= 32
rd_wdata = sext(mul_result, XLEN - 1)
stage3_result_next = regnum_rd
else:
if log:
div_instr_name = {0b100: "div", 0b101: "divu", 0b110: "rem", 0b111: "remu"}[funct3]
@ -253,8 +257,11 @@ class RVCore:
rd_wdata = rs1 if rs2 == 0 else sext((rs1 & XLEN_MASK) % (rs2 & XLEN_MASK), XLEN - 1)
else:
instr_invalid = True
stall_cycles = 18
else:
instr_invalid = True
if not instr_invalid:
stall_cycles += regnum_rs1 == self.stage3_result or regnum_rs2 == self.stage3_result
elif opc == OPC_OP_IMM:
imm = (instr >> 20) - (instr >> 19 & 0x1000) # imm_i(instr)
@ -291,19 +298,24 @@ class RVCore:
instr_invalid = True
else:
instr_invalid = True
if not instr_invalid:
stall_cycles += regnum_rs1 == self.stage3_result
elif opc == OPC_JAL:
rd_wdata = self.pc + 4
# pc_wdata = self.pc + imm_j(instr)
pc_wdata = self.pc + (instr >> 20 & 0x7fe) + (instr >> 9 & 0x800) + (instr & 0xff000) - (instr >> 11 & 0x100000)
if log: log_disasm = f"jal x{regnum_rd}, {pc_wdata & XLEN_MASK:08x}"
stall_cycles = 1
elif opc == OPC_JALR:
stall_cycles += regnum_rs1 == self.stage3_result
imm = imm_i(instr)
if log: log_disasm = f"jalr x{regnum_rd}, x{regnum_rs1}, {imm}"
rd_wdata = self.pc + 4
# JALR clears LSB always
pc_wdata = (rs1 + imm) & -2
stall_cycles = 1
elif opc == OPC_BRANCH:
# target = self.pc + imm_b(instr)
@ -330,8 +342,11 @@ class RVCore:
taken = (rs1 & XLEN_MASK) >= (rs2 & XLEN_MASK)
else:
instr_invalid = True
if not instr_invalid:
stall_cycles += regnum_rs1 == self.stage3_result or regnum_rs2 == self.stage3_result
if taken:
pc_wdata = target
stall_cycles += 1
elif opc == OPC_LOAD:
imm = imm_i(instr)
@ -357,6 +372,9 @@ class RVCore:
rd_wdata = self.mem.get16(load_addr)
else:
instr_invalid = True
if not instr_invalid:
stall_cycles += regnum_rs1 == self.stage3_result
stage3_result_next = regnum_rd
elif opc == OPC_STORE:
imm = imm_s(instr)
@ -373,6 +391,8 @@ class RVCore:
self.mem.put32(store_addr, rs2)
else:
instr_invalid = True
if not instr_invalid:
stall_cycles += regnum_rs1 == self.stage3_result
elif opc == OPC_LUI:
imm = imm_u(instr)
@ -404,6 +424,7 @@ class RVCore:
rd_wdata = self.csr.read(csr_addr)
if csr_write_op == RVCSR.WRITE or rs2 != 0:
self.csr.write(csr_addr, rs2, op=csr_write_op)
stall_cycles += regnum_rs1 == self.stage3_result
elif funct3 in (0b101, 0b110, 0b111):
if log:
instr_name = {0b101: "csrrwi", 0b110: "csrrsi", 0b111: "csrrci"}[funct3]
@ -451,6 +472,9 @@ class RVCore:
print(f"Invalid instruction at {self.pc:08x}: {instr:08x}")
self.csr.step()
if cycle_accurate:
self.csr.mcycle += stall_cycles
self.stage3_result = stage3_result_next if stage3_result_next != 0 else None