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// =======================================================================================
// This Sail RISC-V architecture model, comprising all files and
// directories except where otherwise noted is subject the BSD
// two-clause license in the LICENSE file.
//
// SPDX-License-Identifier: BSD-2-Clause
// =======================================================================================

//
// Types used in supporting extensions for page-table walks.
//
// There are three types involved:
//
// . An accumulator, passed down from the root to the leaves (ext_ptw)
// . Metadata returned with failed permissions checks (ext_ptw_fail)
// . Errors embedded within the PTW_Error union
//
// Information flow begins with init_ext_ptw (: ext_ptw) being routed,
// via the translateNN functions and/or walkNN functions, to the
// checkPTEPermission function, which is the intended point of
// interaction with extensions.
//
// checkPTEPermission will be called repeatedly at each PTE, each call
// seeing the accumulator state generated by a successful result of
// the previous call.  On failure, this function is expected to
// generate, instead, an ext_ptw_fail value as well as a new
// accumulator value, both of which will be returned to the code
// calling into translation.
//
// If translation ultimately succeeds, the final accumulator state is
// captured and will be returned to the code calling into translation.
//
// If translation ultimately fails, the accumulator at the time of
// failure and the ext_ptw_fail value are returned to the caller.  The
// ext_ptw_fail value is used to generate a PTW_Error value by calling
// ext_get_ptw_error; this allows the extension to generate both novel
// (e.g., PTW_Ext_Error) and existing (e.g., PTW_Invalid_PTE) PTW_Error
// values.

type ext_ptw = unit
let init_ext_ptw : ext_ptw = ()

type ext_ptw_fail = unit

// This type can be used for custom errors for page-table-walks,
// and values in this type are typically generated from the final
// result of the ext_ptw at the end of the walk.
type ext_ptw_error = unit // No extensions for page-table-walk errors

// This type supports extensions to the exceptions defined in the ISA.
type ext_exc_type = unit // No exception extensions

// Default translation of PTW errors into exception annotations
function ext_translate_exception(e : ext_ptw_error) -> ext_exc_type =
  e // type pun because both are unit; extensions may need to override this

// Default conversion of extension exceptions to bits
mapping ext_exc_type_bits : ext_exc_type <-> exc_code = {
  // First code for a custom extension
  () <-> 0b011000, // 24
}

// Default conversion of extension exceptions to strings
val ext_exc_type_to_str : ext_exc_type -> string
function ext_exc_type_to_str(e) = "extension-exception"