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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
// =======================================================================================
// default exception model
type ext_exception = unit
// Is XRET from given mode permitted by extension?
function ext_check_xret_priv (_p : Privilege) : Privilege -> bool = true
// Called if above check fails
function ext_fail_xret_priv () : unit -> unit = ()
function handle_trap_extension(_p : Privilege, _pc : xlenbits, _u : option(unit)) -> unit = ()
// used for traps and ECALL
function prepare_trap_vector(p : Privilege, cause : Mcause) -> xlenbits = {
let tvec : Mtvec = match p {
Machine => mtvec,
Supervisor => stvec,
User => internal_error(__FILE__, __LINE__, "Invalid privilege level"),
VirtualUser => internal_error(__FILE__, __LINE__, "Hypervisor extension not supported"),
VirtualSupervisor => internal_error(__FILE__, __LINE__, "Hypervisor extension not supported"),
};
match tvec_addr(tvec, cause) {
Some(epc) => epc,
None() => internal_error(__FILE__, __LINE__, "Invalid tvec mode")
}
}
// xRET handling involves three functions:
//
// get_xepc: used to read the value of the xret target (no control flow transfer)
// set_xepc: used to write a value of the xret target (no control flow transfer)
// prepare_xret_target: used to get the value for control transfer to the xret target
function get_xepc(p : Privilege) -> xlenbits =
match p {
Machine => align_pc(mepc),
Supervisor => align_pc(sepc),
User => internal_error(__FILE__, __LINE__, "Invalid privilege level"),
VirtualUser => internal_error(__FILE__, __LINE__, "Hypervisor extension not supported"),
VirtualSupervisor => internal_error(__FILE__, __LINE__, "Hypervisor extension not supported"),
}
function set_xepc(p : Privilege, value : xlenbits) -> xlenbits = {
let target = legalize_xepc(value);
match p {
Machine => mepc = target,
Supervisor => sepc = target,
User => internal_error(__FILE__, __LINE__, "Invalid privilege level"),
VirtualUser => internal_error(__FILE__, __LINE__, "Hypervisor extension not supported"),
VirtualSupervisor => internal_error(__FILE__, __LINE__, "Hypervisor extension not supported"),
};
target
}
function prepare_xret_target(p : Privilege) -> xlenbits =
get_xepc(p)
// other trap-related CSRs
function get_mtvec() -> xlenbits =
mtvec.bits
function get_stvec() -> xlenbits =
stvec.bits
function set_mtvec(value : xlenbits) -> xlenbits = {
mtvec = legalize_tvec(mtvec, value);
mtvec.bits
}
function set_stvec(value : xlenbits) -> xlenbits = {
stvec = legalize_tvec(stvec, value);
stvec.bits
}
mapping clause csr_name_map = 0x105 <-> "stvec"
mapping clause csr_name_map = 0x141 <-> "sepc"
mapping clause csr_name_map = 0x305 <-> "mtvec"
mapping clause csr_name_map = 0x341 <-> "mepc"
function clause is_CSR_accessible(0x105, _, _) = currentlyEnabled(Ext_S) // stvec
function clause is_CSR_accessible(0x141, _, _) = currentlyEnabled(Ext_S) // sepc
function clause is_CSR_accessible(0x305, _, _) = true // mtvec
function clause is_CSR_accessible(0x341, _, _) = true // mepc
function clause read_CSR(0x105) = get_stvec()
function clause read_CSR(0x141) = get_xepc(Supervisor)
function clause read_CSR(0x305) = get_mtvec()
function clause read_CSR(0x341) = get_xepc(Machine)
function clause write_CSR(0x105, value) = { Ok(set_stvec(value)) }
function clause write_CSR(0x141, value) = { Ok(set_xepc(Supervisor, value)) }
function clause write_CSR(0x305, value) = { Ok(set_mtvec(value)) }
function clause write_CSR(0x341, value) = { Ok(set_xepc(Machine, value)) }
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