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type xlen = atom(64)
type xlen_t = bits(64)
type regno ('n : Int), 0 <= 'n < 32 = atom('n)
type regbits = bits(5)
val zeros : forall 'n, 'n >= 0. atom('n) -> bits('n)
function zeros n = replicate_bits(0b0, n)
val cast regbits_to_regno : bits(5) -> {'n, 0 <= 'n < 32. regno('n)}
function regbits_to_regno b = let r as atom(_) = unsigned(b) in r
/* Architectural state */
register PC : xlen_t
register nextPC : xlen_t
register Xs : vector(32, dec, xlen_t)
/* Getters and setters for X registers (special case for zeros register, x0) */
val rX : forall 'n, 0 <= 'n < 32. regno('n) -> xlen_t effect {rreg}
function rX 0 = 0x0000000000000000
and rX (r if r > 0) = Xs[r]
val wX : forall 'n, 0 <= 'n < 32. (regno('n), xlen_t) -> unit effect {wreg}
function wX (r, v) =
if (r != 0) then {
Xs[r] = v;
}
overload X = {rX, wX}
/* Accessors for memory */
val MEMr : forall 'n, 'n >= 0. (xlen_t, atom('n)) -> bits(8 * 'n) effect {rmem}
function MEMr (addr, width) =
match __RISCV_read(addr, width, false, false, false) { Some(v) => v, None() => zeros(8 * width) }
/* Instruction decode and execute */
enum iop = {RISCV_ADDI, RISCV_SLTI, RISCV_SLTIU, RISCV_XORI, RISCV_ORI, RISCV_ANDI} /* immediate ops */
scattered union ast
val decode : bits(32) -> option(ast) effect pure
scattered function decode
val execute : ast -> unit effect {rmem, rreg, wreg}
scattered function execute
/* ****************************************************************** */
/* ADDI */
union clause ast = ITYPE : (bits(12), regbits, regbits, iop)
function clause decode imm : bits(12) @ rs1 : regbits @ 0b000 @ rd : regbits @ 0b0010011
= Some(ITYPE(imm, rs1, rd, RISCV_ADDI))
function clause execute (ITYPE (imm, rs1, rd, RISCV_ADDI)) =
let rs1_val = X(rs1) in
let imm_ext : xlen_t = EXTS(imm) in
let result = rs1_val + imm_ext in
X(rd) = result
/* ****************************************************************** */
/* Load double */
union clause ast = LOAD : (bits(12), regbits, regbits)
function clause decode imm : bits(12) @ rs1 : regbits @ 0b011 @ rd : regbits @ 0b0000011
= Some(LOAD(imm, rs1, rd))
function clause execute(LOAD(imm, rs1, rd)) =
let addr : xlen_t = X(rs1) + EXTS(imm) in
let result : xlen_t = MEMr(addr, 8) in
X(rd) = result
/* ****************************************************************** */
function clause decode _ = None()
end ast
end decode
end execute
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