riscv_platform.sail

/*=======================================================================================*/
/*  RISCV Sail Model                                                                     */
/*                                                                                       */
/*  This Sail RISC-V architecture model, comprising all files and                        */
/*  directories except for the snapshots of the Lem and Sail libraries                   */
/*  in the prover_snapshots directory (which include copies of their                     */
/*  licences), is subject to the BSD two-clause licence below.                           */
/*                                                                                       */
/*  Copyright (c) 2017-2021                                                              */
/*    Prashanth Mundkur                                                                  */
/*    Rishiyur S. Nikhil and Bluespec, Inc.                                              */
/*    Jon French                                                                         */
/*    Brian Campbell                                                                     */
/*    Robert Norton-Wright                                                               */
/*    Alasdair Armstrong                                                                 */
/*    Thomas Bauereiss                                                                   */
/*    Shaked Flur                                                                        */
/*    Christopher Pulte                                                                  */
/*    Peter Sewell                                                                       */
/*    Alexander Richardson                                                               */
/*    Hesham Almatary                                                                    */
/*    Jessica Clarke                                                                     */
/*    Microsoft, for contributions by Robert Norton-Wright and Nathaniel Wesley Filardo  */
/*    Peter Rugg                                                                         */
/*    Aril Computer Corp., for contributions by Scott Johnson                            */
/*                                                                                       */
/*  All rights reserved.                                                                 */
/*                                                                                       */
/*  This software was developed by the above within the Rigorous                         */
/*  Engineering of Mainstream Systems (REMS) project, partly funded by                   */
/*  EPSRC grant EP/K008528/1, at the Universities of Cambridge and                       */
/*  Edinburgh.                                                                           */
/*                                                                                       */
/*  This software was developed by SRI International and the University of               */
/*  Cambridge Computer Laboratory (Department of Computer Science and                    */
/*  Technology) under DARPA/AFRL contract FA8650-18-C-7809 ("CIFV"), and                 */
/*  under DARPA contract HR0011-18-C-0016 ("ECATS") as part of the DARPA                 */
/*  SSITH research programme.                                                            */
/*                                                                                       */
/*  This project has received funding from the European Research Council                 */
/*  (ERC) under the European Union’s Horizon 2020 research and innovation                */
/*  programme (grant agreement 789108, ELVER).                                           */
/*                                                                                       */
/*                                                                                       */
/*  Redistribution and use in source and binary forms, with or without                   */
/*  modification, are permitted provided that the following conditions                   */
/*  are met:                                                                             */
/*  1. Redistributions of source code must retain the above copyright                    */
/*     notice, this list of conditions and the following disclaimer.                     */
/*  2. Redistributions in binary form must reproduce the above copyright                 */
/*     notice, this list of conditions and the following disclaimer in                   */
/*     the documentation and/or other materials provided with the                        */
/*     distribution.                                                                     */
/*                                                                                       */
/*  THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS''                   */
/*  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED                    */
/*  TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A                      */
/*  PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR                  */
/*  CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,                         */
/*  SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT                     */
/*  LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF                     */
/*  USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND                  */
/*  ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,                   */
/*  OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT                   */
/*  OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF                   */
/*  SUCH DAMAGE.                                                                         */
/*=======================================================================================*/

/* Platform-specific definitions, and basic MMIO devices. */

/* Current constraints on this implementation are:
   - it cannot access memory directly, but instead provides definitions for the physical memory model
   - it can access system register state, needed to manipulate interrupt bits
   - it relies on externs to get platform address information and doesn't hardcode them
*/

val elf_tohost = {
  ocaml: "Elf_loader.elf_tohost",
  interpreter: "Elf_loader.elf_tohost",
  c: "elf_tohost"
} :  unit -> int

val elf_entry = {
  ocaml: "Elf_loader.elf_entry",
  interpreter: "Elf_loader.elf_entry",
  c: "elf_entry"
} : unit -> int

/* Main memory */
val plat_ram_base = {c: "plat_ram_base", ocaml: "Platform.dram_base", interpreter: "Platform.dram_base", lem: "plat_ram_base"} : unit -> xlenbits
val plat_ram_size = {c: "plat_ram_size", ocaml: "Platform.dram_size", interpreter: "Platform.dram_size", lem: "plat_ram_size"} : unit -> xlenbits

/* whether the platform supports PMP configurations */
val plat_enable_pmp = {ocaml: "Platform.enable_pmp",
                       interpreter: "Platform.enable_pmp",
                       c: "plat_enable_pmp",
                       lem: "plat_enable_pmp"} : unit -> bool

/* whether the MMU should update dirty bits in PTEs */
val plat_enable_dirty_update = {ocaml: "Platform.enable_dirty_update",
                                interpreter: "Platform.enable_dirty_update",
                                c: "plat_enable_dirty_update",
                                lem: "plat_enable_dirty_update"} : unit -> bool

/* whether the platform supports misaligned accesses without trapping to M-mode. if false,
 * misaligned loads/stores are trapped to Machine mode.
 */
val plat_enable_misaligned_access = {ocaml: "Platform.enable_misaligned_access",
                                     interpreter: "Platform.enable_misaligned_access",
                                     c: "plat_enable_misaligned_access",
                                     lem: "plat_enable_misaligned_access"} : unit -> bool

/* whether mtval stores the bits of a faulting instruction on illegal instruction exceptions */
val plat_mtval_has_illegal_inst_bits = {ocaml: "Platform.mtval_has_illegal_inst_bits",
                                        interpreter: "Platform.mtval_has_illegal_inst_bits",
                                        c: "plat_mtval_has_illegal_inst_bits",
                                        lem: "plat_mtval_has_illegal_inst_bits"} : unit -> bool

/* ROM holding reset vector and device-tree DTB */
val plat_rom_base   = {ocaml: "Platform.rom_base", interpreter: "Platform.rom_base", c: "plat_rom_base", lem: "plat_rom_base"} : unit -> xlenbits
val plat_rom_size   = {ocaml: "Platform.rom_size", interpreter: "Platform.rom_size", c: "plat_rom_size", lem: "plat_rom_size"} : unit -> xlenbits

/* Location of clock-interface, which should match with the spec in the DTB */
val plat_clint_base = {ocaml: "Platform.clint_base", interpreter: "Platform.clint_base", c: "plat_clint_base", lem: "plat_clint_base"} : unit -> xlenbits
val plat_clint_size = {ocaml: "Platform.clint_size", interpreter: "Platform.clint_size", c: "plat_clint_size", lem: "plat_clint_size"} : unit -> xlenbits

/* Location of HTIF ports */
val plat_htif_tohost = {ocaml: "Platform.htif_tohost", c: "plat_htif_tohost", lem: "plat_htif_tohost"} : unit -> xlenbits
function plat_htif_tohost () = to_bits(sizeof(xlen), elf_tohost ())
// todo: fromhost

val phys_mem_segments : unit -> list((xlenbits, xlenbits))
function phys_mem_segments() =
  (plat_rom_base (), plat_rom_size ()) ::
  (plat_ram_base (), plat_ram_size ()) ::
  [||]

/* Physical memory map predicates */

function within_phys_mem forall 'n, 'n <= max_mem_access. (addr : xlenbits, width : atom('n)) -> bool = {
  /* To avoid overflow issues when physical memory extends to the end
   * of the addressable range, we need to perform address bound checks
   * on unsigned unbounded integers.
   */
  let addr_int     = unsigned(addr);
  let ram_base_int = unsigned(plat_ram_base ());
  let rom_base_int = unsigned(plat_rom_base ());
  let ram_size_int = unsigned(plat_ram_size ());
  let rom_size_int = unsigned(plat_rom_size ());

  /* todo: iterate over segment list */
  if      (  ram_base_int <= addr_int
           & (addr_int + sizeof('n)) <= (ram_base_int + ram_size_int))
  then    true
  else if (  rom_base_int <= addr_int
           & (addr_int + sizeof('n)) <= (rom_base_int + rom_size_int))
  then    true
  else {
    print_platform("within_phys_mem: " ^ BitStr(addr) ^ " not within phys-mem:");
    print_platform("  plat_rom_base: " ^ BitStr(plat_rom_base ()));
    print_platform("  plat_rom_size: " ^ BitStr(plat_rom_size ()));
    print_platform("  plat_ram_base: " ^ BitStr(plat_ram_base ()));
    print_platform("  plat_ram_size: " ^ BitStr(plat_ram_size ()));
    false
  }
}

function within_clint forall 'n, 0 < 'n <= max_mem_access . (addr : xlenbits, width : atom('n)) -> bool = {
  /* To avoid overflow issues when physical memory extends to the end
   * of the addressable range, we need to perform address bound checks
   * on unsigned unbounded integers.
   */
  let addr_int       = unsigned(addr);
  let clint_base_int = unsigned(plat_clint_base ());
  let clint_size_int = unsigned(plat_clint_size ());
    clint_base_int <= addr_int
  & (addr_int + sizeof('n)) <= (clint_base_int + clint_size_int)
}

function within_htif_writable forall 'n, 0 < 'n <= max_mem_access . (addr : xlenbits, width : atom('n)) -> bool =
    plat_htif_tohost() == addr | (plat_htif_tohost() + 4 == addr & width == 4)

function within_htif_readable forall 'n, 0 < 'n <= max_mem_access . (addr : xlenbits, width : atom('n)) -> bool =
    plat_htif_tohost() == addr | (plat_htif_tohost() + 4 == addr & width == 4)

/* CLINT (Core Local Interruptor), based on Spike. */

val plat_insns_per_tick = {ocaml: "Platform.insns_per_tick", interpreter: "Platform.insns_per_tick", c: "plat_insns_per_tick", lem: "plat_insns_per_tick"} : unit -> int

// assumes a single hart, since this typically is a vector of per-hart registers.
register mtimecmp : bits(64)  // memory-mapped internal clint register.

/* CLINT memory-mapped IO */

/* relative address map:
 *
 * 0000 msip hart 0         -- memory-mapped software interrupt
 * 0004 msip hart 1
 * 4000 mtimecmp hart 0 lo  -- memory-mapped timer thresholds
 * 4004 mtimecmp hart 0 hi
 * 4008 mtimecmp hart 1 lo
 * 400c mtimecmp hart 1 hi
 * bff8 mtime lo            -- memory-mapped clocktimer value
 * bffc mtime hi
 */

let MSIP_BASE        : xlenbits = EXTZ(0x00000)
let MTIMECMP_BASE    : xlenbits = EXTZ(0x04000)
let MTIMECMP_BASE_HI : xlenbits = EXTZ(0x04004)
let MTIME_BASE       : xlenbits = EXTZ(0x0bff8)
let MTIME_BASE_HI    : xlenbits = EXTZ(0x0bffc)

val clint_load : forall 'n, 'n > 0. (AccessType(ext_access_type), xlenbits, int('n)) -> MemoryOpResult(bits(8 * 'n)) effect {rreg}
function clint_load(t, addr, width) = {
  let addr = addr - plat_clint_base ();
  /* FIXME: For now, only allow exact aligned access. */
  if addr == MSIP_BASE & ('n == 8 | 'n == 4)
  then {
    if   get_config_print_platform()
    then print_platform("clint[" ^ BitStr(addr) ^ "] -> " ^ BitStr(mip.MSI()));
    MemValue(sail_zero_extend(mip.MSI(), sizeof(8 * 'n)))
  }
  else if addr == MTIMECMP_BASE & ('n == 4)
  then {
    if   get_config_print_platform()
    then print_platform("clint<4>[" ^ BitStr(addr) ^ "] -> " ^ BitStr(mtimecmp[31..0]));
    /* FIXME: Redundant zero_extend currently required by Lem backend */
    MemValue(sail_zero_extend(mtimecmp[31..0], 32))
  }
  else if addr == MTIMECMP_BASE & ('n == 8)
  then {
    if   get_config_print_platform()
    then print_platform("clint<8>[" ^ BitStr(addr) ^ "] -> " ^ BitStr(mtimecmp));
    /* FIXME: Redundant zero_extend currently required by Lem backend */
    MemValue(sail_zero_extend(mtimecmp, 64))
  }
  else if addr == MTIMECMP_BASE_HI & ('n == 4)
  then {
    if   get_config_print_platform()
    then print_platform("clint-hi<4>[" ^ BitStr(addr) ^ "] -> " ^ BitStr(mtimecmp[63..32]));
    /* FIXME: Redundant zero_extend currently required by Lem backend */
    MemValue(sail_zero_extend(mtimecmp[63..32], 32))
  }
  else if addr == MTIME_BASE & ('n == 4)
  then {
    if   get_config_print_platform()
    then print_platform("clint[" ^ BitStr(addr) ^ "] -> " ^ BitStr(mtime));
    MemValue(sail_zero_extend(mtime[31..0], 32))
  }
  else if addr == MTIME_BASE & ('n == 8)
  then {
    if   get_config_print_platform()
    then print_platform("clint[" ^ BitStr(addr) ^ "] -> " ^ BitStr(mtime));
    MemValue(sail_zero_extend(mtime, 64))
  }
  else if addr == MTIME_BASE_HI & ('n == 4)
  then {
    if   get_config_print_platform()
    then print_platform("clint[" ^ BitStr(addr) ^ "] -> " ^ BitStr(mtime));
    MemValue(sail_zero_extend(mtime[63..32], 32))
  }
  else {
    if   get_config_print_platform()
    then print_platform("clint[" ^ BitStr(addr) ^ "] -> <not-mapped>");
    match t {
      Execute()  => MemException(E_Fetch_Access_Fault()),
      Read(Data) => MemException(E_Load_Access_Fault()),
      _          => MemException(E_SAMO_Access_Fault())
    }
  }
}

function clint_dispatch() -> unit = {
  if   get_config_print_platform()
  then print_platform("clint::tick mtime <- " ^ BitStr(mtime));
  mip->MTI() = 0b0;
  if mtimecmp <=_u mtime then {
    if   get_config_print_platform()
    then print_platform(" clint timer pending at mtime " ^ BitStr(mtime));
    mip->MTI() = 0b1
  }
}

/* The rreg effect is due to checking mtime. */
val clint_store: forall 'n, 'n > 0. (xlenbits, int('n), bits(8 * 'n)) -> MemoryOpResult(bool) effect {rreg,wreg}
function clint_store(addr, width, data) = {
  let addr = addr - plat_clint_base ();
  if addr == MSIP_BASE & ('n == 8 | 'n == 4) then {
    if   get_config_print_platform()
    then print_platform("clint[" ^ BitStr(addr) ^ "] <- " ^ BitStr(data) ^ " (mip.MSI <- " ^ BitStr(data[0]) ^ ")");
    mip->MSI() = [data[0]];
    clint_dispatch();
    MemValue(true)
  } else if addr == MTIMECMP_BASE & 'n == 8 then {
    if   get_config_print_platform()
    then print_platform("clint<8>[" ^ BitStr(addr) ^ "] <- " ^ BitStr(data) ^ " (mtimecmp)");
    mtimecmp = sail_zero_extend(data, 64); /* FIXME: Redundant zero_extend currently required by Lem backend */
    clint_dispatch();
    MemValue(true)
  } else if addr == MTIMECMP_BASE & 'n == 4 then {
    if   get_config_print_platform()
    then print_platform("clint<4>[" ^ BitStr(addr) ^ "] <- " ^ BitStr(data) ^ " (mtimecmp)");
    mtimecmp = vector_update_subrange(mtimecmp, 31, 0, sail_zero_extend(data, 32));  /* FIXME: Redundant zero_extend currently required by Lem backend */
    clint_dispatch();
    MemValue(true)
  } else if addr == MTIMECMP_BASE_HI & 'n == 4 then {
    if   get_config_print_platform()
    then print_platform("clint<4>[" ^ BitStr(addr) ^ "] <- " ^ BitStr(data) ^ " (mtimecmp)");
    mtimecmp = vector_update_subrange(mtimecmp, 63, 32, sail_zero_extend(data, 32)); /* FIXME: Redundant zero_extend currently required by Lem backend */
    clint_dispatch();
    MemValue(true)
  } else {
    if   get_config_print_platform()
    then print_platform("clint[" ^ BitStr(addr) ^ "] <- " ^ BitStr(data) ^ " (<unmapped>)");
    MemException(E_SAMO_Access_Fault())
  }
}

val tick_clock : unit -> unit effect {rreg, wreg}
function tick_clock() = {
  if   mcountinhibit.CY() == 0b0
  then mcycle = mcycle + 1;

  mtime  = mtime  + 1;
  clint_dispatch()
}

/* Basic terminal character I/O. */

val plat_term_write = {ocaml: "Platform.term_write", c: "plat_term_write", lem: "plat_term_write"} : bits(8) -> unit
val plat_term_read  = {ocaml: "Platform.term_read",  c: "plat_term_read", lem: "plat_term_read"}  : unit -> bits(8)

/* Spike's HTIF device interface, which multiplexes the above MMIO devices. */

bitfield htif_cmd : bits(64) = {
  device  : 63 .. 56,
  cmd     : 55 .. 48,
  payload : 47 .. 0
}

register htif_tohost : bits(64)
register htif_done   : bool
register htif_exit_code : bits(64)

/* Applications sometimes write the lower 32-bit payload bytes without
   writing the control bytes; this is seen in the riscv-tests suite.
   However, processing the payload bytes too early could miss a
   subsequent write to the control bytes.  As a workaround, if the
   payload is written a few times with the same value, without an
   intervening write to the control bytes, we process the whole htif
   command anyway.  */

register htif_cmd_write : bit
register htif_payload_writes : bits(4)

/* Once a htif command has been processed, the port is reset. */
function reset_htif () -> unit = {
  htif_cmd_write = bitzero;
  htif_payload_writes = 0x0;
  htif_tohost = EXTZ(0b0);
}

/* Since the htif tohost port is only available at a single address,
 * we'll assume here that physical memory model has correctly
 * dispatched the address.
 */

val htif_load : forall 'n, 'n > 0. (AccessType(ext_access_type), xlenbits, int('n)) -> MemoryOpResult(bits(8 * 'n)) effect {rreg}
function htif_load(t, paddr, width) = {
  if   get_config_print_platform()
  then print_platform("htif[" ^ BitStr(paddr) ^ "] -> " ^ BitStr(htif_tohost));
  /* FIXME: For now, only allow the expected access widths. */
  if      width == 8 & (paddr == plat_htif_tohost())
  then    MemValue(sail_zero_extend(htif_tohost, 64))         /* FIXME: Redundant zero_extend currently required by Lem backend */
  else if width == 4 & paddr == plat_htif_tohost()
  then    MemValue(sail_zero_extend(htif_tohost[31..0], 32))  /* FIXME: Redundant zero_extend currently required by Lem backend */
  else if width == 4 & paddr == plat_htif_tohost() + 4
  then    MemValue(sail_zero_extend(htif_tohost[63..32], 32)) /* FIXME: Redundant zero_extend currently required by Lem backend */
  else match t {
    Execute()  => MemException(E_Fetch_Access_Fault()),
    Read(Data) => MemException(E_Load_Access_Fault()),
    _          => MemException(E_SAMO_Access_Fault())
  }
}

/* The rreg,wreg effects are an artifact of using 'register' to implement device state. */
val htif_store: forall 'n, 0 < 'n <= 8. (xlenbits, int('n), bits(8 * 'n)) -> MemoryOpResult(bool) effect {rreg,wreg}
function htif_store(paddr, width, data) = {
  if   get_config_print_platform()
  then print_platform("htif[" ^ BitStr(paddr) ^ "] <- " ^ BitStr(data));
  /* Store the written value so that we can ack it later. */
  if      width == 8
  then    { htif_cmd_write = bitone;
            htif_payload_writes = htif_payload_writes + 1;
            htif_tohost = EXTZ(data) }
  else if width == 4 & paddr == plat_htif_tohost()
  then    { if   data == htif_tohost[31 .. 0]
            then htif_payload_writes = htif_payload_writes + 1
            else htif_payload_writes = 0x1;
            htif_tohost = vector_update_subrange(htif_tohost, 31, 0, data) }
  else if width == 4 & paddr == plat_htif_tohost() + 4
  then    { if   data[15 .. 0] == htif_tohost[47 .. 32]
            then htif_payload_writes = htif_payload_writes + 1
            else htif_payload_writes = 0x1;
            htif_cmd_write = bitone;
            htif_tohost = vector_update_subrange(htif_tohost, 63, 32, data) }
  /* unaligned command writes are not supported and will not be detected */
  else    { htif_tohost = EXTZ(data) };

  /* Execute if there were repeated writes of the same payload without
   * a cmd (e.g. in riscv-tests), or we have a complete htif command.
   */
  if   (((htif_cmd_write == bitone) & (unsigned(htif_payload_writes) > 0))
        | (unsigned(htif_payload_writes) > 2))
  then {
    let cmd = Mk_htif_cmd(htif_tohost);
    match cmd.device() {
      0x00 => { /* syscall-proxy */
        if   get_config_print_platform()
        then print_platform("htif-syscall-proxy cmd: " ^ BitStr(cmd.payload()));
        if   cmd.payload()[0] == bitone
        then {
             htif_done = true;
             htif_exit_code = (sail_zero_extend(cmd.payload(), 64) >> 1)
        }
        else ()
      },
      0x01 => { /* terminal */
        if   get_config_print_platform()
        then print_platform("htif-term cmd: " ^ BitStr(cmd.payload()));
        match cmd.cmd() {
          0x00 => /* TODO: terminal input handling */ (),
          0x01 => plat_term_write(cmd.payload()[7..0]),
          c    => print("Unknown term cmd: " ^ BitStr(c))
        };
        /* reset to ack */
        reset_htif()
      },
      d => print("htif-???? cmd: " ^ BitStr(data))
    }
  };
  MemValue(true)
}

val htif_tick : unit -> unit effect {rreg, wreg}
function htif_tick() = {
  if   get_config_print_platform()
  then print_platform("htif::tick " ^ BitStr(htif_tohost));
  htif_tohost = htif_tohost /* prevent this function being optimized out */
}

/* Top-level MMIO dispatch */
$ifndef RVFI_DII
function within_mmio_readable forall 'n, 0 < 'n <= max_mem_access . (addr : xlenbits, width : atom('n)) -> bool =
  within_clint(addr, width) | (within_htif_readable(addr, width) & 1 <= 'n)
$else
function within_mmio_readable forall 'n, 0 < 'n <= max_mem_access . (addr : xlenbits, width : atom('n)) -> bool = false
$endif

$ifndef RVFI_DII
function within_mmio_writable forall 'n, 0 < 'n <= max_mem_access . (addr : xlenbits, width : atom('n)) -> bool =
  within_clint(addr, width) | (within_htif_writable(addr, width) & 'n <= 8)
$else
function within_mmio_writable forall 'n, 0 < 'n <= max_mem_access . (addr : xlenbits, width : atom('n)) -> bool = false
$endif

function mmio_read forall 'n, 0 < 'n <= max_mem_access . (t : AccessType(ext_access_type), paddr : xlenbits, width : atom('n)) -> MemoryOpResult(bits(8 * 'n)) =
  if   within_clint(paddr, width)
  then clint_load(t, paddr, width)
  else if within_htif_readable(paddr, width) & (1 <= 'n)
  then htif_load(t, paddr, width)
  else match t {
    Execute()  => MemException(E_Fetch_Access_Fault()),
    Read(Data) => MemException(E_Load_Access_Fault()),
    _          => MemException(E_SAMO_Access_Fault())
  }

function mmio_write forall 'n, 0 <'n <= max_mem_access . (paddr : xlenbits, width : atom('n), data: bits(8 * 'n)) -> MemoryOpResult(bool) =
  if   within_clint(paddr, width)
  then clint_store(paddr, width, data)
  else if within_htif_writable(paddr, width) & 'n <= 8
  then htif_store(paddr, width, data)
  else MemException(E_SAMO_Access_Fault())

/* Platform initialization and ticking. */

function init_platform() -> unit = {
  htif_tohost = EXTZ(0b0);
  htif_done   = false;
  htif_exit_code = EXTZ(0b0);
  htif_cmd_write = bitzero;
  htif_payload_writes = EXTZ(0b0);
}

function tick_platform() -> unit = {
  htif_tick();
}

/* Platform-specific handling of instruction faults */

function handle_illegal() -> unit = {
  let info = if plat_mtval_has_illegal_inst_bits ()
             then Some(instbits)
             else None();
  let t : sync_exception = struct { trap    = E_Illegal_Instr(),
                                    excinfo = info,
                                    ext     = None() };
  set_next_pc(exception_handler(cur_privilege, CTL_TRAP(t), PC))
}

/* Platform-specific wait-for-interrupt */

function platform_wfi() -> unit = {
  cancel_reservation();
  /* speed execution by getting the timer to fire at the next instruction,
   * since we currently don't have any other devices raising interrupts.
   */
  if mtime <_u mtimecmp then {
    mtime  = mtimecmp;
    mcycle = mtimecmp;
  }
}