ed917c394f
Along with the mypy tool, this helps find bugs in the Python code handling the instruction definition data structures.
76 lines
1.9 KiB
Python
76 lines
1.9 KiB
Python
"""
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RISC-V Encoding recipes.
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The encoding recipes defined here more or less correspond to the RISC-V native
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instruction formats described in the reference:
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The RISC-V Instruction Set Manual
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Volume I: User-Level ISA
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Version 2.1
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"""
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from __future__ import absolute_import
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from cretonne import EncRecipe
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from cretonne.formats import Binary, BinaryImm
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from cretonne.predicates import IsSignedInt
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# The low 7 bits of a RISC-V instruction is the base opcode. All 32-bit
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# instructions have 11 as the two low bits, with bits 6:2 determining the base
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# opcode.
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#
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# Encbits for the 32-bit recipes are opcode[6:2] | (funct3 << 5) | ...
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# The functions below encode the encbits.
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def LOAD(funct3):
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# type: (int) -> int
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assert funct3 <= 0b111
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return 0b00000 | (funct3 << 5)
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def STORE(funct3):
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# type: (int) -> int
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assert funct3 <= 0b111
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return 0b01000 | (funct3 << 5)
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def BRANCH(funct3):
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# type: (int) -> int
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assert funct3 <= 0b111
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return 0b11000 | (funct3 << 5)
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def OPIMM(funct3, funct7=0):
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# type: (int, int) -> int
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assert funct3 <= 0b111
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return 0b00100 | (funct3 << 5) | (funct7 << 8)
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def OPIMM32(funct3, funct7=0):
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# type: (int, int) -> int
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assert funct3 <= 0b111
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return 0b00110 | (funct3 << 5) | (funct7 << 8)
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def OP(funct3, funct7):
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# type: (int, int) -> int
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assert funct3 <= 0b111
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assert funct7 <= 0b1111111
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return 0b01100 | (funct3 << 5) | (funct7 << 8)
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def OP32(funct3, funct7):
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# type: (int, int) -> int
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assert funct3 <= 0b111
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assert funct7 <= 0b1111111
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return 0b01110 | (funct3 << 5) | (funct7 << 8)
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# R-type 32-bit instructions: These are mostly binary arithmetic instructions.
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# The encbits are `opcode[6:2] | (funct3 << 5) | (funct7 << 8)
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R = EncRecipe('R', Binary)
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# R-type with an immediate shift amount instead of rs2.
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Rshamt = EncRecipe('Rshamt', BinaryImm)
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I = EncRecipe('I', BinaryImm, instp=IsSignedInt(BinaryImm.imm, 12))
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