///////////////////////////////////////////
// trap.sv
//
// Written: David_Harris@hmc.edu 9 January 2021
// Modified: dottolia@hmc.edu 14 April 2021: Add support for vectored interrupts
//
// Purpose: Handle Traps: Exceptions and Interrupts
// See RISC-V Privileged Mode Specification 20190608 3.1.10-11
//
// A component of the Wally configurable RISC-V project.
//
// Copyright (C) 2021 Harvey Mudd College & Oklahoma State University
//
// MIT LICENSE
// Permission is hereby granted, free of charge, to any person obtaining a copy of this
// software and associated documentation files (the "Software"), to deal in the Software
// without restriction, including without limitation the rights to use, copy, modify, merge,
// publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons
// to whom the Software is furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all copies or
// substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
// BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
// TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE
// OR OTHER DEALINGS IN THE SOFTWARE.
////////////////////////////////////////////////////////////////////////////////////////////////
`include "wally-config.vh"
module trap (
input logic clk,
input logic reset,
(* mark_debug = "true" *) input logic InstrMisalignedFaultM, InstrAccessFaultM, IllegalInstrFaultM,
(* mark_debug = "true" *) input logic BreakpointFaultM, LoadMisalignedFaultM, StoreAmoMisalignedFaultM,
(* mark_debug = "true" *) input logic LoadAccessFaultM, StoreAmoAccessFaultM, EcallFaultM, InstrPageFaultM,
(* mark_debug = "true" *) input logic LoadPageFaultM, StoreAmoPageFaultM,
(* mark_debug = "true" *) input logic mretM, sretM, uretM,
input logic [1:0] PrivilegeModeW, NextPrivilegeModeM,
(* mark_debug = "true" *) input logic [`XLEN-1:0] MEPC_REGW, SEPC_REGW, UEPC_REGW, UTVEC_REGW, STVEC_REGW, MTVEC_REGW,
(* mark_debug = "true" *) input logic [11:0] MIP_REGW, MIE_REGW, SIP_REGW, SIE_REGW,
input logic STATUS_MIE, STATUS_SIE,
input logic [`XLEN-1:0] PCM,
input logic [`XLEN-1:0] InstrMisalignedAdrM, IEUAdrM,
input logic [31:0] InstrM,
input logic InstrValidM, CommittedM, DivE,
output logic TrapM, MTrapM, STrapM, UTrapM, RetM,
output logic InterruptM,
output logic ExceptionM,
output logic PendingInterruptM,
output logic [`XLEN-1:0] PrivilegedNextPCM, CauseM, NextFaultMtvalM
// output logic [11:0] MIP_REGW, SIP_REGW, UIP_REGW, MIE_REGW, SIE_REGW, UIE_REGW,
// input logic WriteMIPM, WriteSIPM, WriteUIPM, WriteMIEM, WriteSIEM, WriteUIEM
);
logic MIntGlobalEnM, SIntGlobalEnM;
(* mark_debug = "true" *) logic [11:0] PendingIntsM;
//logic InterruptM;
logic [`XLEN-1:0] PrivilegedTrapVector, PrivilegedVectoredTrapVector;
logic Exception1M;
// Determine pending enabled interrupts
// interrupt if any sources are pending
// & with a M stage valid bit to avoid interrupts from interrupt a nonexistent flushed instruction (in the M stage)
// & with ~CommittedM to make sure MEPC isn't chosen so as to rerun the same instr twice
assign MIntGlobalEnM = (PrivilegeModeW != `M_MODE) | STATUS_MIE; // if M ints enabled or lower priv 3.1.9
assign SIntGlobalEnM = (PrivilegeModeW == `U_MODE) | ((PrivilegeModeW == `S_MODE) & STATUS_SIE); // if in lower priv mode, or if S ints enabled and not in higher priv mode 3.1.9
assign PendingIntsM = ((MIP_REGW & MIE_REGW) & ({12{MIntGlobalEnM}} & 12'h888)) | ((SIP_REGW & SIE_REGW) & ({12{SIntGlobalEnM}} & 12'h222));
assign PendingInterruptM = (|PendingIntsM) & InstrValidM;
assign InterruptM = PendingInterruptM & ~(CommittedM); // *** RT. temporary hack to prevent integer division from having an interrupt during divide.
// Trigger Traps and RET
// According to RISC-V Spec Section 1.6, exceptions are caused by instructions. Interrupts are external asynchronous.
// Traps are the union of exceptions and interrupts.
assign ExceptionM = InstrMisalignedFaultM | InstrAccessFaultM | IllegalInstrFaultM |
LoadMisalignedFaultM | StoreAmoMisalignedFaultM |
InstrPageFaultM | LoadPageFaultM | StoreAmoPageFaultM |
BreakpointFaultM | EcallFaultM |
LoadAccessFaultM | StoreAmoAccessFaultM;
assign TrapM = ExceptionM | InterruptM; // *** clean this up later DH
assign MTrapM = TrapM & (NextPrivilegeModeM == `M_MODE);
assign STrapM = TrapM & (NextPrivilegeModeM == `S_MODE) & `S_SUPPORTED;
assign UTrapM = TrapM & (NextPrivilegeModeM == `U_MODE) & `N_SUPPORTED;
assign RetM = mretM | sretM | uretM;
always_comb
if (NextPrivilegeModeM == `U_MODE) PrivilegedTrapVector = UTVEC_REGW;
else if (NextPrivilegeModeM == `S_MODE) PrivilegedTrapVector = STVEC_REGW;
else PrivilegedTrapVector = MTVEC_REGW;
// Handle vectored traps (when mtvec/stvec/utvec csr value has bits [1:0] == 01)
// For vectored traps, set program counter to _tvec value + 4 times the cause code
//
// POSSIBLE OPTIMIZATION:
// From 20190608 privielegd spec page 27 (3.1.7)
// > Allowing coarser alignments in Vectored mode enables vectoring to be
// > implemented without a hardware adder circuit.
// For example, we could require m/stvec be aligned on 7 bits to let us replace the adder directly below with
// [untested] PrivilegedVectoredTrapVector = {PrivilegedTrapVector[`XLEN-1:7], CauseM[3:0], 4'b0000}
if(`VECTORED_INTERRUPTS_SUPPORTED) begin:vec
always_comb
if (PrivilegedTrapVector[1:0] == 2'b01 & CauseM[`XLEN-1] == 1)
PrivilegedVectoredTrapVector = {PrivilegedTrapVector[`XLEN-1:2] + {CauseM[`XLEN-5:0], 2'b00}, 2'b00};
else
PrivilegedVectoredTrapVector = {PrivilegedTrapVector[`XLEN-1:2], 2'b00};
end
else begin
assign PrivilegedVectoredTrapVector = {PrivilegedTrapVector[`XLEN-1:2], 2'b00};
end
always_comb
if (mretM) PrivilegedNextPCM = MEPC_REGW;
else if (sretM) PrivilegedNextPCM = SEPC_REGW;
else if (uretM) PrivilegedNextPCM = UEPC_REGW;
else PrivilegedNextPCM = PrivilegedVectoredTrapVector;
// Cause priority defined in table 3.7 of 20190608 privileged spec
// Exceptions are of lower priority than all interrupts (3.1.9)
always_comb
if (reset) CauseM = 0; // hard reset 3.3
else if (PendingIntsM[11]) CauseM = (1 << (`XLEN-1)) + 11; // Machine External Int
else if (PendingIntsM[3]) CauseM = (1 << (`XLEN-1)) + 3; // Machine Sw Int
else if (PendingIntsM[7]) CauseM = (1 << (`XLEN-1)) + 7; // Machine Timer Int
else if (PendingIntsM[9]) CauseM = (1 << (`XLEN-1)) + 9; // Supervisor External Int
else if (PendingIntsM[1]) CauseM = (1 << (`XLEN-1)) + 1; // Supervisor Sw Int
else if (PendingIntsM[5]) CauseM = (1 << (`XLEN-1)) + 5; // Supervisor Timer Int
else if (InstrPageFaultM) CauseM = 12;
else if (InstrAccessFaultM) CauseM = 1;
else if (InstrMisalignedFaultM) CauseM = 0;
else if (IllegalInstrFaultM) CauseM = 2;
else if (BreakpointFaultM) CauseM = 3;
else if (EcallFaultM) CauseM = {{(`XLEN-2){1'b0}}, PrivilegeModeW} + 8;
else if (LoadMisalignedFaultM) CauseM = 4;
else if (StoreAmoMisalignedFaultM) CauseM = 6;
else if (LoadPageFaultM) CauseM = 13;
else if (StoreAmoPageFaultM) CauseM = 15;
else if (LoadAccessFaultM) CauseM = 5;
else if (StoreAmoAccessFaultM) CauseM = 7;
else CauseM = 0;
// MTVAL
// 3.1.17: on instruction fetch, load, or store address misaligned access or page fault
// mtval is written with the faulting virtual address.
// On illegal instruction trap, mtval may be written with faulting instruction
// For other traps (including interrupts), mtval is set to 0
// *** hardware breakpoint is supposed to write faulting virtual address per priv p. 38
// *** Page faults not yet implemented
// Technically
always_comb
if (InstrMisalignedFaultM) NextFaultMtvalM = InstrMisalignedAdrM;
else if (LoadMisalignedFaultM) NextFaultMtvalM = IEUAdrM;
else if (StoreAmoMisalignedFaultM) NextFaultMtvalM = IEUAdrM;
else if (BreakpointFaultM) NextFaultMtvalM = PCM;
else if (InstrPageFaultM) NextFaultMtvalM = PCM;
else if (LoadPageFaultM) NextFaultMtvalM = IEUAdrM;
else if (StoreAmoPageFaultM) NextFaultMtvalM = IEUAdrM;
else if (IllegalInstrFaultM) NextFaultMtvalM = {{(`XLEN-32){1'b0}}, InstrM};
else NextFaultMtvalM = 0;
endmodule