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Moved the decoding of opcodes into a separate module and optimised memory reads

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This commit is contained in:
(Tim) Efthimis Kritikos 2023-02-17 18:08:09 +00:00
parent ed3d7101d3
commit 82bd859874
5 changed files with 536 additions and 419 deletions
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2
8086_documentation.md
View File

@ -23,6 +23,8 @@ On some instructions:
* **V**-bit : V-bit decides the number of shifts for rotate and shift instructions. If V = 0, then count = 1; if V = 1, the count is in CL register. For example, if V = 1 and CL = 2 then shift or rotate instruction shifts or rotates 2-bits
* **Z**-bit : Used as a compare bit with the zero flag in conditional repeat and loop instructions. ex branch if zero is set or clear.
No instruction has parts of its opcode past the first 2 bytes I.e. all bytes after the first two are additional data bytes
| Register ID / REG | Register Name |
|:-------------------:|:-------------:|
| 0 0 0 | AL AX |

2
common.mk
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@ -40,7 +40,7 @@ disas: $(subst .txt,.disas,${BOOT_CODE})
%.run: %.txt ${SYSTEM_VVP}
${QUIET_VVP}
${Q}vvp "${SYSTEM_VVP}" +BOOT_CODE="$<"
${Q}vvp -i "${SYSTEM_VVP}" +BOOT_CODE="$<"
%.disas: %.bin
objdump -D -b binary -m i8086 $^ | less

2
system/Makefile
View File

@ -15,7 +15,7 @@
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
#
SOURCES=processor.v testbench.v memory.v registers.v alu.v
SOURCES=processor.v testbench.v memory.v registers.v alu.v decoder.v
INCLUDES=proc_state_def.v alu_header.v config.v
SYSTEM_VVP=system.vvp
BOOT_CODE=boot_code.txt

447
system/decoder.v Normal file
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@ -0,0 +1,447 @@
/* decoder.v - Implementation of instruction opcode decoding logic
This file is part of the 9086 project.
Copyright (c) 2023 Efthymios Kritikos
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
`include "proc_state_def.v"
`include "alu_header.v"
module decoder(
input wire [15:0] CIR,input wire [15:0] FLAGS, output reg Wbit, output reg Sbit, output reg unaligning ,output reg opcode_size, output reg ERROR,output reg [`PROC_STATE_BITS-1:0]next_state
,output reg [1:0]MOD, output reg [2:0]RM, output reg [15:0] PARAM1,output reg [15:0] PARAM2,output reg HALT,output reg has_operands
,output reg [1:0]in_alu1_sel1,output reg [1:0]in_alu1_sel2,output reg [2:0]out_alu1_sel
,output reg [3:0]reg_read_port1_addr, output reg [3:0]reg_write_addr
,output reg [2:0]ALU_1OP
);
/* 0 0 0 0 0 0 0 0 | 0 0 0 0 0 0 0 0 | 0 0 0 0 0 0 0 0 | 0 0 0 0 0 0 0 0 */
`define invalid_instruction next_state=`PROC_IF_STATE_ENTRY;ERROR=1;MOD=2'b11;
`define start_aligning_instruction unaligning=0;
`define start_unaligning_instruction unaligning=1;
always @( CIR ) begin
ERROR=0;HALT=0;
MOD=2'b11;/*TODO:remove*/
case(CIR[15:10])
6'b000001 : begin
/* ADD, ... */
if ( CIR[9:9] == 0 )begin
/* Add Immediate word/byte to accumulator */
/* 0 0 0 0 0 1 0 W | DATA | DATA if W |*/
opcode_size=0;
has_operands=1;
Wbit=CIR[8:8];
if(Wbit)
`start_unaligning_instruction
else
`start_aligning_instruction
MOD=2'b11;
in_alu1_sel1=2'b00;
in_alu1_sel2=2'b01;
out_alu1_sel=3'b011;
reg_read_port1_addr={CIR[8:8],3'b000};
reg_write_addr={CIR[8:8],3'b000};
ALU_1OP=`ALU_OP_ADD;
if(CIR[8:8]==1)
next_state=`PROC_DE_LOAD_16_PARAM;
else begin
PARAM1[7:0]=CIR[7:0];
next_state=`PROC_EX_STATE_ENTRY;
end
end else begin
`invalid_instruction
end
end
6'b100000 : begin
/* ADD, ADC, SUB, SBB, CMP , AND, ... */
case (CIR[5:3])
3'b000 : begin
/* Add Immediate word/byte to register/memory */
/* 1 0 0 0 0 0 S W | MOD 0 0 0 R/M | < DISP LO > | < DISP HI > | DATA | DATA if W | */
opcode_size=1;
has_operands=1;
`start_aligning_instruction
Wbit=CIR[8:8];
MOD=2'b11;
in_alu1_sel1=2'b00;
in_alu1_sel2=2'b01;
out_alu1_sel={1'b0,CIR[7:6]};
reg_read_port1_addr={CIR[8:8],CIR[2:0]};
reg_write_addr={CIR[8:8],CIR[2:0]};
ALU_1OP=`ALU_OP_ADD;
next_state=`PROC_DE_LOAD_16_PARAM;
if(CIR[8:8]==1)
next_state=`PROC_DE_LOAD_16_PARAM;
else begin
`invalid_instruction /*do 8bit loads*/
end
end
3'b111 : begin
/* CMP - compare Immediate with register / memory */
/* 1 0 0 0 0 0 S W | MOD 0 0 0 R/M | < DISP LO > | < DISP HI > | DATA | DATA if W | */
opcode_size=1;
has_operands=1;
Wbit=CIR[8:8];
Sbit=CIR[9:9];
MOD=CIR[7:6];
if((Wbit==1)&&(CIR[9:9]==1))begin
`start_unaligning_instruction
end else begin
`invalid_instruction;
end
if(MOD==2'b11)begin
in_alu1_sel1=2'b00;
in_alu1_sel2=2'b01;
reg_read_port1_addr={CIR[8:8],CIR[2:0]};
out_alu1_sel=3'b100;
ALU_1OP=`ALU_OP_SUB;
next_state=`PROC_DE_LOAD_8_PARAM;
end else begin
`invalid_instruction
end
end
default:begin
`invalid_instruction
end
endcase
end
6'b101100,
6'b101101:begin
/* MOV - Move Immediate byte to register */
/* 1 0 1 1 W REG | DATA | DATA if W |*/
has_operands=1;
Wbit=CIR[11:11];
opcode_size=0;
if(Wbit)
`start_unaligning_instruction
else
`start_aligning_instruction
MOD=2'b11;
in_alu1_sel1=2'b00;
in_alu1_sel2=2'b00;
out_alu1_sel=3'b011;
reg_write_addr={1'b0,CIR[10:8]};
PARAM1[7:0]=CIR[7:0];
PARAM2=0;
ALU_1OP=`ALU_OP_ADD;
next_state=`PROC_EX_STATE_ENTRY;
end
6'b101110,
6'b101111 : begin
/*MOV - Move Immediate word to register*/
has_operands=1;
Wbit=CIR[11:11];
opcode_size=0;
if(Wbit)
`start_unaligning_instruction
else
`start_aligning_instruction
MOD=2'b11;
in_alu1_sel1=2'b00;
in_alu1_sel2=2'b00;
out_alu1_sel=3'b011;
reg_write_addr={1'b1,CIR[10:8]};
ALU_1OP=`ALU_OP_ADD;
PARAM2=0;
next_state=`PROC_DE_LOAD_16_PARAM;
end
6'b100010 : begin
/* MOV - Reg/Mem to/from register */
/* 1 0 0 0 1 0 D W | MOD REG RM | < DISP LO > | < DISP HI > |*/
has_operands=0;
`start_aligning_instruction
opcode_size=1;
MOD=CIR[7:6];
RM=CIR[2:0];
Wbit=CIR[8:8];
in_alu1_sel2=2'b00;
if(CIR[9:9] == 1)begin
/* Mem/Reg to reg */
if(MOD==2'b11)begin
/*Reg to Reg*/
in_alu1_sel1=2'b01;
reg_read_port1_addr=CIR[2:0];
next_state=`PROC_EX_STATE_ENTRY;
end else begin
/*Mem to Reg*/
in_alu1_sel1=2'b00;
next_state=`RPOC_MEMIO_READ;
end
out_alu1_sel=3'b011;
reg_write_addr={Wbit,CIR[5:3]};
end else begin
/* Reg to Mem/Reg */
if(MOD==2'b11)begin
/*Reg to Reg*/
in_alu1_sel1=2'b01;
out_alu1_sel=3'b011;
reg_write_addr={Wbit,CIR[2:0]};
next_state=`PROC_EX_STATE_ENTRY;
end else begin
/*Reg to Mem*/
in_alu1_sel1=2'b00;
reg_read_port1_addr=CIR[5:3];
out_alu1_sel={1'b0,MOD};
next_state=`PROC_DE_LOAD_REG_TO_PARAM;
end
reg_read_port1_addr={Wbit,CIR[5:3]};
end
ALU_1OP=`ALU_OP_ADD;
PARAM2=0;
end
6'b010000,//INC
6'b010001,//INC
6'b010010,//DEC
6'b010011:begin//DEC
/* DEC - Decrement Register */
/* | 0 1 0 0 1 REG | */
/* INC - Increment Register */
/* | 0 1 0 0 0 REG | */
has_operands=0;
opcode_size=0;
`start_unaligning_instruction
Wbit=1;
in_alu1_sel1=2'b01;
in_alu1_sel2=2'b00;
out_alu1_sel=3'b011;
MOD=2'b11;
PARAM2=1;
reg_read_port1_addr={1'b1,CIR[10:8]};
reg_write_addr={1'b1,CIR[10:8]};
if(CIR[11:11]==0)
ALU_1OP=`ALU_OP_ADD;
else
ALU_1OP=`ALU_OP_SUB;
next_state=`PROC_EX_STATE_ENTRY;
end
6'b111111 : begin
/* INC */
if (CIR[9:9] == 1 ) begin
case (CIR[5:3])
3'b000,3'b001 :begin
/* INC - Register/Memory */
/* 1 1 1 1 1 1 1 W | MOD 0 0 0 R/M | < DISP LO> | < DISP HI> */
/* DEC - Register/Memory */
/* 1 1 1 1 1 1 1 W | MOD 0 0 1 R/M | < DISP LO> | < DISP HI> */
has_operands=1;
opcode_size=1;
`start_aligning_instruction
Wbit=CIR[8:8];
MOD=CIR[7:6];
RM=CIR[2:0];
in_alu1_sel1=(MOD==2'b11)? 2'b01 : 2'b00;
in_alu1_sel2=2'b00;/* number 1 */
out_alu1_sel={1'b0,MOD};
PARAM2=1;
/*in case MOD=11 */
reg_read_port1_addr={1'b0,RM};
reg_write_addr={1'b0,RM};
ALU_1OP=(CIR[3:3]==1)?`ALU_OP_SUB:`ALU_OP_ADD;
if ( CIR[7:6] == 2'b11 )
next_state=`PROC_EX_STATE_ENTRY;
else
next_state=`RPOC_MEMIO_READ;
end
default:begin
`invalid_instruction
end
endcase
end else begin
`invalid_instruction
end
end
6'b111101 : begin
/*HLT, CMC, TEST, NOT, NEG, MUL, IMUL, .... */
case (CIR[9:8])
2'b00:begin
/* HLT - Halt */
/* 1 1 1 1 0 1 0 0 | */
has_operands=0;
opcode_size=0;
`start_unaligning_instruction
MOD=2'b11;
HALT=1;
next_state=`PROC_HALT_STATE;
end
default:begin
`invalid_instruction;
end
endcase
end
6'b001111 : begin
if ( CIR[9:9] == 0 ) begin
/* CMP - Compare Immediate with accumulator */
/* 0 0 1 1 1 1 0 W | DATA | DATA if W |*/
/* */
/* NOTE: 8086 doc doesn't show the third byte but the */
/* W flag and my assembler seem to disagree */
Wbit=CIR[8:8];
opcode_size=0;
has_operands=1;
if(Wbit)
`start_unaligning_instruction
else
`start_aligning_instruction
MOD=2'b11;
in_alu1_sel1=2'b00;
in_alu1_sel2=2'b01;
reg_read_port1_addr={CIR[8:8],3'b000};
out_alu1_sel=3'b100;
ALU_1OP=`ALU_OP_SUB;
if(CIR[8:8]==1)
next_state=`PROC_DE_LOAD_16_PARAM;
else begin
PARAM1[7:0]=CIR[7:0];
next_state=`PROC_EX_STATE_ENTRY;
end
end else begin
`invalid_instruction
end
end
6'b011100,
6'b011101,
6'b011110,
6'b011111:begin
/* Conditional relative jumps */
/* JE/JZ - Jump on Zero */
/* 0 1 1 1 0 1 0 0 | IP-INC8 |*/
/* JS - Jump on Sign */
/* 0 1 1 1 1 0 0 0 | IP-INC8 |*/
/* JNS -Jump on not Sign */
/* 0 1 1 1 1 0 0 1 | IP-INC8 |*/
/* .... */
has_operands=1;
`start_aligning_instruction
Wbit=1;
opcode_size=0;
in_alu1_sel1=2'b10;
in_alu1_sel2=2'b00;
PARAM2={{8{CIR[7:7]}},CIR[7:0]};
ALU_1OP=`ALU_OP_ADD_SIGNED_B;
out_alu1_sel=3'b101;
case(CIR[11:9])
4'b000: begin
/* Jump on (not) Overflow */
if(FLAGS[11:11]==CIR[8:8])
next_state=`PROC_IF_STATE_ENTRY;
else begin
next_state=`PROC_EX_STATE_ENTRY;
end
end
4'b010: begin
/* Jump on (not) Zero */
if(FLAGS[6:6]==CIR[8:8])
next_state=`PROC_IF_STATE_ENTRY;
else
next_state=`PROC_EX_STATE_ENTRY;
end
4'b100: begin
/* Jump on (not) Sign */
if(FLAGS[7:7]==CIR[8:8])
next_state=`PROC_IF_STATE_ENTRY;
else
next_state=`PROC_EX_STATE_ENTRY;
end
4'b101: begin
/* Jump on (not) Parity */
if(FLAGS[2:2]==CIR[8:8])
next_state=`PROC_IF_STATE_ENTRY;
else
next_state=`PROC_EX_STATE_ENTRY;
end
default:begin
`invalid_instruction; /*We don't support that condition*/
end
endcase
end
6'b111010:begin
/* JMP,CALL */
case(CIR[9:8])
2'b00: begin
/* CALL - Call direct within segment */
/* 1 1 1 0 1 0 0 0 | IP-INC-LO | IP-INC-HI |*/
`invalid_instruction
end
2'b01: begin
/* JMP - Uncoditional Jump direct within segment */
/* 1 1 1 0 1 0 0 1 | IP-INC-LO | IP-INC-HI |*/
`invalid_instruction
end
2'b10: begin
/* JMP - Unconditional jump direct intersegment */
/* 0 0 0 0 0 0 0 0 | IP-LO | IP-HI | CS-LO | CS-HI | */
`invalid_instruction
end
2'b11: begin
/* JMP - Unconditional jump direct within segment (short) */
/* | 1 1 1 0 1 0 0 1 | IP-INC-LO | */
`start_aligning_instruction
opcode_size=0;
has_operands=1;
Wbit=1;
in_alu1_sel1=2'b10;
in_alu1_sel2=2'b00;
PARAM2={{8{CIR[7:7]}},CIR[7:0]};
ALU_1OP=`ALU_OP_ADD_SIGNED_B;
out_alu1_sel=3'b101;
next_state=`PROC_EX_STATE_ENTRY;
end
endcase
end
6'b110011:begin
case(CIR[9:8])
2'b00:begin
`invalid_instruction
end
2'b01:begin
if(CIR[7:0]==8'h21) begin
/* INT - execut interrupt handler */
/* 1 1 0 0 1 1 0 1 | DATA |*/
has_operands=1;
opcode_size=0;
`start_aligning_instruction
/* Emulate MS-DOS print routines */
$write("%s" ,register_file.registers[2][7:0]); /*TODO:Could trigger erroneously while CIR is not final*/
next_state=`PROC_IF_STATE_ENTRY;
end else begin
`invalid_instruction
end
end
2'b10:begin
`invalid_instruction
end
2'b11:begin
`invalid_instruction
end
endcase
end
default:begin
`invalid_instruction
end
endcase
end
endmodule

502
system/processor.v
View File

@ -42,16 +42,33 @@ assign external_data_bus=read?data_bus_output_register:'hz;
// State
reg [`PROC_STATE_BITS-1:0] state;
/* Decoder */
wire Wbit, Sbit, unaligning_instruction;
wire [`PROC_STATE_BITS-1:0] next_state;
wire [1:0]MOD;
wire [2:0]RM;
wire [15:0]DE_PARAM1;
wire [15:0]DE_PARAM2;
wire DE_ERROR,DE_HALT;
wire [3:0]DE_reg_read_port1_addr,DE_reg_write_addr;
wire opcode_size;
wire has_operands;
decoder decoder(
CIR,FLAGS,Wbit,Sbit,unaligning_instruction,opcode_size,DE_ERROR,next_state
,MOD,RM,DE_PARAM1,DE_PARAM2,DE_HALT,has_operands
,in_alu1_sel1,in_alu1_sel2,out_alu1_sel
,DE_reg_read_port1_addr,DE_reg_write_addr
,ALU_1OP
);
// Registers
reg [19:0] ProgCount; /*TODO consider having single circuit to increment PC instead of having possible lots of adders all over the code*/
reg [15:0] CIR;
reg [15:0] PARAM1;
reg [15:0] PARAM2;
reg one_byte_instruction;
reg unaligned_access;
reg [1:0]MOD;
reg [2:0]RM;
reg Wbit;
reg Sbit;
reg [15:0]FLAGS;
/* . . . . O D I T S Z . A . P . C */
// C - Carry flag : carry out or borrow into the high order bit (8bit/16bit)
@ -90,7 +107,7 @@ always @(negedge reset) begin
@(posedge reset)
@(negedge clock);
state=`PROC_IF_STATE_ENTRY;
MOD=2'b11;
one_byte_instruction=0;
ERROR=0;
end
end
@ -144,28 +161,32 @@ wire [7:0] ALU_1FLAGS;
ALU ALU1(ALU_1A,ALU_1B,ALU_1OE,ALU_1O,ALU_1OP,ALU_1FLAGS,Wbit);
/*** Processor stages ***/
`define invalid_instruction state=`PROC_IF_STATE_ENTRY;ERROR=1;MOD=2'b11;
`define start_aligning_instruction if(unaligned_access==0)begin ProgCount=ProgCount+1; external_address_bus <= ProgCount; end /*we normally don't advance PC in case of singly byte unaligning instructions leaving us with two instructions in one read so do that here*/
`define start_unaligning_instruction unaligned_access=~unaligned_access;
`define invalid_instruction state=`PROC_IF_STATE_ENTRY;ERROR=1;
always @(negedge clock) begin
case(state)
`PROC_IF_WRITE_CIR:begin
if(unaligned_access)begin
CIR[15:8] <= external_data_bus[7:0];
ProgCount=ProgCount+1;
state=`PROC_IF_STATE_EXTRA_FETCH_SET;
if(one_byte_instruction==1)begin /*TODO: have a read buffer so we can do this even with data reads */
CIR <= {CIR[7:0],external_data_bus[15:8]};
state=`PROC_DE_STATE_ENTRY;
end else begin
CIR[15:8] <= external_data_bus[7:0];
state=`PROC_IF_STATE_EXTRA_FETCH_SET;
end
end else begin
CIR <= external_data_bus;
ProgCount=ProgCount+1;
state=`PROC_DE_STATE_ENTRY;
end
end
`PROC_IF_STATE_EXTRA_FETCH:begin
CIR[7:0] <= external_data_bus[15:8];
state=`PROC_DE_STATE_ENTRY;
ALU_1OE=0;
end
`PROC_EX_STATE_EXIT:begin
unaligned_access=unaligning_instruction^unaligned_access;
case(out_alu1_sel) /*TODO: use RM*/
3'b000,
3'b001,
@ -274,6 +295,7 @@ always @(negedge clock) begin
endcase
end
always @(posedge clock) begin
case(state)
`PROC_HALT_STATE:begin
@ -296,431 +318,77 @@ always @(posedge clock) begin
reg_write_in_sel=2'b00;
end
`PROC_IF_STATE_EXTRA_FETCH_SET:begin
ProgCount=ProgCount+1;
external_address_bus <= ProgCount;
state=`PROC_IF_STATE_EXTRA_FETCH;
end
/* 0 0 0 0 0 0 0 0 | 0 0 0 0 0 0 0 0 | 0 0 0 0 0 0 0 0 | 0 0 0 0 0 0 0 0 */
/* AFTER THE IF STAGE WE HAVE THE FIRST BYTE OF THE
* INSTRUCTION AND THE ONE FOLLOWING, ALIGNED CORRECTLY TO
* CIR */
`PROC_DE_STATE_ENTRY:begin
case(CIR[15:10])
6'b000001 : begin
/* ADD, ... */
if ( CIR[9:9] == 0 )begin
/* Add Immediate word/byte to accumulator */
/* 0 0 0 0 0 1 0 W | DATA | DATA if W |*/
Wbit=CIR[8:8];
if(Wbit)
`start_unaligning_instruction
else
`start_aligning_instruction
MOD=2'b11;
in_alu1_sel1=2'b00;
in_alu1_sel2=2'b01;
out_alu1_sel=3'b011;
reg_read_port1_addr={CIR[8:8],3'b000};
reg_write_addr={CIR[8:8],3'b000};
ALU_1OE=0;
ALU_1OP=`ALU_OP_ADD;
if(CIR[8:8]==1)
state=`PROC_DE_LOAD_16_PARAM;
else begin
PARAM1[7:0]=CIR[7:0];
state=`PROC_EX_STATE_ENTRY;
end
end else begin
`invalid_instruction
end
end
6'b100000 : begin
/* ADD, ADC, SUB, SBB, CMP , AND, ... */
case (CIR[5:3])
3'b000 : begin
/* Add Immediate word/byte to register/memory */
/* 1 0 0 0 0 0 S W | MOD 0 0 0 R/M | < DISP LO > | < DISP HI > | DATA | DATA if W | */
`start_aligning_instruction
Wbit=CIR[8:8];
MOD=2'b11;
in_alu1_sel1=2'b00;
in_alu1_sel2=2'b01;
out_alu1_sel={1'b0,CIR[7:6]};
reg_read_port1_addr={CIR[8:8],CIR[2:0]};
reg_write_addr={CIR[8:8],CIR[2:0]};
ALU_1OE=0;
ALU_1OP=`ALU_OP_ADD;
state=`PROC_DE_LOAD_16_PARAM;
if(CIR[8:8]==1)
state=`PROC_DE_LOAD_16_PARAM;
else begin
`invalid_instruction /*do 8bit loads*/
end
end
3'b111 : begin
/* CMP - compare Immediate with register / memory */
/* 1 0 0 0 0 0 S W | MOD 0 0 0 R/M | < DISP LO > | < DISP HI > | DATA | DATA if W | */
Wbit=CIR[8:8];
Sbit=CIR[9:9];
MOD=CIR[7:6];
if((Wbit==1)&&(CIR[9:9]==1))begin
`start_unaligning_instruction
end else begin
`invalid_instruction;
end
if(MOD==2'b11)begin
in_alu1_sel1=2'b00;
in_alu1_sel2=2'b01;
reg_read_port1_addr={CIR[8:8],CIR[2:0]};
out_alu1_sel=3'b100;
ALU_1OE=0;
ALU_1OP=`ALU_OP_SUB;
state=`PROC_DE_LOAD_8_PARAM;
end else begin
`invalid_instruction
end
end
default:begin
`invalid_instruction
end
endcase
end
6'b101100,
6'b101101:begin
/* MOV - Move Immediate byte to register */
/* 1 0 1 1 W REG | DATA | DATA if W |*/
Wbit=CIR[11:11];
if(Wbit)
`start_unaligning_instruction
else
`start_aligning_instruction
MOD=2'b11;
in_alu1_sel1=2'b00;
in_alu1_sel2=2'b00;
out_alu1_sel=3'b011;
reg_write_addr={1'b0,CIR[10:8]};
PARAM1[7:0]=CIR[7:0];
PARAM2=0;
ALU_1OE=0;
ALU_1OP=`ALU_OP_ADD;
state=`PROC_EX_STATE_ENTRY;
end
6'b101110,
6'b101111 : begin
/*MOV - Move Immediate word to register*/
Wbit=CIR[11:11];
if(Wbit)
`start_unaligning_instruction
else
`start_aligning_instruction
MOD=2'b11;
in_alu1_sel1=2'b00;
in_alu1_sel2=2'b00;
out_alu1_sel=3'b011;
reg_write_addr={1'b1,CIR[10:8]};
ALU_1OE=0;
ALU_1OP=`ALU_OP_ADD;
PARAM2=0;
state=`PROC_DE_LOAD_16_PARAM;
end
6'b100010 : begin
/* MOV - Reg/Mem to/from register */
/* 1 0 0 0 1 0 D W | MOD REG RM | < DISP LO > | < DISP HI > |*/
`start_aligning_instruction
MOD=CIR[7:6];
RM=CIR[2:0];
Wbit=CIR[8:8];
in_alu1_sel2=2'b00;
if(CIR[9:9] == 1)begin
/* Mem/Reg to reg */
if(MOD==2'b11)begin
/*Reg to Reg*/
in_alu1_sel1=2'b01;
reg_read_port1_addr=CIR[2:0];
state=`PROC_EX_STATE_ENTRY;
end else begin
/*Mem to Reg*/
in_alu1_sel1=2'b00;
state=`RPOC_MEMIO_READ;
end
out_alu1_sel=3'b011;
reg_write_addr={Wbit,CIR[5:3]};
end else begin
/* Reg to Mem/Reg */
if(MOD==2'b11)begin
/*Reg to Reg*/
in_alu1_sel1=2'b01;
out_alu1_sel=3'b011;
reg_write_addr={Wbit,CIR[2:0]};
state=`PROC_EX_STATE_ENTRY;
end else begin
/*Reg to Mem*/
in_alu1_sel1=2'b00;
reg_read_port1_addr=CIR[5:3];
out_alu1_sel={1'b0,MOD};
state=`PROC_DE_LOAD_REG_TO_PARAM;
end
reg_read_port1_addr={Wbit,CIR[5:3]};
end
ALU_1OE=0;
ALU_1OP=`ALU_OP_ADD;
PARAM2=0;
end
6'b010000,//INC
6'b010001,//INC
6'b010010,//DEC
6'b010011:begin//DEC
/* DEC - Decrement Register */
/* | 0 1 0 0 1 REG | */
/* INC - Increment Register */
/* | 0 1 0 0 0 REG | */
`start_unaligning_instruction
Wbit=1;
in_alu1_sel1=2'b01;
in_alu1_sel2=2'b00;
out_alu1_sel=3'b011;
MOD=2'b11;
PARAM2=1;
reg_read_port1_addr={1'b1,CIR[10:8]};
reg_write_addr={1'b1,CIR[10:8]};
ALU_1OE=0;
if(CIR[11:11]==0)
ALU_1OP=`ALU_OP_ADD;
else
ALU_1OP=`ALU_OP_SUB;
state=`PROC_EX_STATE_ENTRY;
end
6'b111111 : begin
/* INC */
if (CIR[9:9] == 1 ) begin
case (CIR[5:3])
3'b000,3'b001 :begin
/* INC - Register/Memory */
/* 1 1 1 1 1 1 1 W | MOD 0 0 0 R/M | < DISP LO> | < DISP HI> */
/* DEC - Register/Memory */
/* 1 1 1 1 1 1 1 W | MOD 0 0 1 R/M | < DISP LO> | < DISP HI> */
`start_aligning_instruction
Wbit=CIR[8:8];
MOD=CIR[7:6];
RM=CIR[2:0];
in_alu1_sel1=(MOD==2'b11)? 2'b01 : 2'b00;
in_alu1_sel2=2'b00;/* number 1 */
out_alu1_sel={1'b0,MOD};
PARAM2=1;
/*in case MOD=11 */
reg_read_port1_addr={1'b0,RM};
reg_write_addr={1'b0,RM};
ALU_1OE=0;
ALU_1OP=(CIR[3:3]==1)?`ALU_OP_SUB:`ALU_OP_ADD;
if ( CIR[7:6] == 2'b11 )
state=`PROC_EX_STATE_ENTRY;
else
state=`RPOC_MEMIO_READ;
end
default:begin
`invalid_instruction
end
endcase
end else begin
`invalid_instruction
end
end
6'b111101 : begin
/*HLT, CMC, TEST, NOT, NEG, MUL, IMUL, .... */
case (CIR[9:8])
2'b00:begin
/* HLT - Halt */
/* 1 1 1 1 0 1 0 0 | */
`start_unaligning_instruction
MOD=2'b11;
HALT=1;
state=`PROC_HALT_STATE;
end
default:begin
`invalid_instruction;
end
endcase
end
6'b001111 : begin
if ( CIR[9:9] == 0 ) begin
/* CMP - Compare Immediate with accumulator */
/* 0 0 1 1 1 1 0 W | DATA | DATA if W |*/
/* */
/* NOTE: 8086 doc doesn't show the third byte but the */
/* W flag and my assembler seem to disagree */
Wbit=CIR[8:8];
if(Wbit)
`start_unaligning_instruction
else
`start_aligning_instruction
MOD=2'b11;
in_alu1_sel1=2'b00;
in_alu1_sel2=2'b01;
reg_read_port1_addr={CIR[8:8],3'b000};
out_alu1_sel=3'b100;
ALU_1OE=0;
ALU_1OP=`ALU_OP_SUB;
if(CIR[8:8]==1)
state=`PROC_DE_LOAD_16_PARAM;
else begin
PARAM1[7:0]=CIR[7:0];
state=`PROC_EX_STATE_ENTRY;
end
end else begin
`invalid_instruction
end
end
6'b011100,
6'b011101,
6'b011110,
6'b011111:begin
/* Conditional relative jumps */
/* JE/JZ - Jump on Zero */
/* 0 1 1 1 0 1 0 0 | IP-INC8 |*/
/* JS - Jump on Sign */
/* 0 1 1 1 1 0 0 0 | IP-INC8 |*/
/* JNS -Jump on not Sign */
/* 0 1 1 1 1 0 0 1 | IP-INC8 |*/
/* .... */
`start_aligning_instruction
Wbit=1;
in_alu1_sel1=2'b10;
in_alu1_sel2=2'b00;
PARAM2={{8{CIR[7:7]}},CIR[7:0]};
ALU_1OE=0;
ALU_1OP=`ALU_OP_ADD_SIGNED_B;
out_alu1_sel=3'b101;
case(CIR[11:9])
4'b000: begin
/* Jump on (not) Overflow */
if(FLAGS[11:11]==CIR[8:8])
state=`PROC_IF_STATE_ENTRY;
else begin
state=`PROC_EX_STATE_ENTRY;
end
end
4'b010: begin
/* Jump on (not) Zero */
if(FLAGS[6:6]==CIR[8:8])
state=`PROC_IF_STATE_ENTRY;
else
state=`PROC_EX_STATE_ENTRY;
end
4'b100: begin
/* Jump on (not) Sign */
if(FLAGS[7:7]==CIR[8:8])
state=`PROC_IF_STATE_ENTRY;
else
state=`PROC_EX_STATE_ENTRY;
end
4'b101: begin
/* Jump on (not) Parity */
if(FLAGS[2:2]==CIR[8:8])
state=`PROC_IF_STATE_ENTRY;
else
state=`PROC_EX_STATE_ENTRY;
end
default:begin
`invalid_instruction; /*We don't support that condition*/
end
endcase
end
6'b111010:begin
/* JMP,CALL */
case(CIR[9:8])
2'b00: begin
/* CALL - Call direct within segment */
/* 1 1 1 0 1 0 0 0 | IP-INC-LO | IP-INC-HI |*/
`invalid_instruction
end
2'b01: begin
/* JMP - Uncoditional Jump direct within segment */
/* 1 1 1 0 1 0 0 1 | IP-INC-LO | IP-INC-HI |*/
`invalid_instruction
end
2'b10: begin
/* JMP - Unconditional jump direct intersegment */
/* 0 0 0 0 0 0 0 0 | IP-LO | IP-HI | CS-LO | CS-HI | */
`invalid_instruction
end
2'b11: begin
/* JMP - Unconditional jump direct within segment (short) */
/* | 1 1 1 0 1 0 0 1 | IP-INC-LO | */
`start_aligning_instruction
Wbit=1;
in_alu1_sel1=2'b10;
in_alu1_sel2=2'b00;
PARAM2={{8{CIR[7:7]}},CIR[7:0]};
ALU_1OE=0;
ALU_1OP=`ALU_OP_ADD_SIGNED_B;
out_alu1_sel=3'b101;
state=`PROC_EX_STATE_ENTRY;
end
endcase
end
6'b110011:begin
case(CIR[9:8])
2'b00:begin
`invalid_instruction
end
2'b01:begin
if(CIR[7:0]==8'h21) begin
/* INT - execut interrupt handler */
/* 1 1 0 0 1 1 0 1 | DATA |*/
`start_aligning_instruction
/* Emulate MS-DOS print routines */
$write("%s" ,register_file.registers[2][7:0]);
state=`PROC_IF_STATE_ENTRY;
end else begin
`invalid_instruction
end
end
2'b10:begin
`invalid_instruction
end
2'b11:begin
`invalid_instruction
end
endcase
end
default:begin
`invalid_instruction
end
endcase
/* IF we are unaligned, the address bus contains the
* ProgCount and points to the second word containing
* the nest unread byte in extenral_data_bus[7:0]. If
* we are aligned the address bus points to the first
* word of the instruction which contains no useful
* data anymore but the ProgCount has the correct
* address so update it now so that whatever the case
* external_data_bus contains at leat some unkown data */
one_byte_instruction=(!has_operands)&&(!opcode_size);
external_address_bus <= ProgCount;
state=next_state;
PARAM1=DE_PARAM1;
PARAM2=DE_PARAM2;
ERROR=DE_ERROR;
HALT=DE_HALT;
reg_read_port1_addr=DE_reg_read_port1_addr;
reg_write_addr=DE_reg_write_addr;
end
`PROC_DE_LOAD_REG_TO_PARAM:begin
PARAM1=reg_read_port1_data;
state=`PROC_EX_STATE_ENTRY;
end
`PROC_DE_LOAD_8_PARAM:begin
ProgCount=ProgCount+1;
if(unaligned_access==0)begin
if(opcode_size==0)begin
if({Sbit,Wbit}==2'b11)begin
PARAM1 = {{8{external_data_bus[7:7]}},external_data_bus[7:0]};
/*signed "16bit" read*/
PARAM1 = {{8{CIR[7:7]}},CIR[7:0]};
end else begin
PARAM1[7:0] = external_data_bus[7:0];
PARAM1[7:0] = CIR[7:0];
end
state=`PROC_EX_STATE_ENTRY;
end else begin
external_address_bus=ProgCount;
state=`PROC_DE_LOAD_8_PARAM_UNALIGNED;
if(unaligned_access==1)begin
if({Sbit,Wbit}==2'b11)begin
/*signed "16bit" read*/
PARAM1 = {{8{external_data_bus[7:7]}},external_data_bus[7:0]};
end else begin
PARAM1[7:0] = external_data_bus[7:0];
end
ProgCount=ProgCount+1;
state=`PROC_EX_STATE_ENTRY;
end else begin
external_address_bus=ProgCount;
state=`PROC_DE_LOAD_8_PARAM_UNALIGNED;
end
end
end
`PROC_DE_LOAD_16_PARAM:begin
if(unaligned_access==1)begin
PARAM1[7:0] = external_data_bus[7:0];
ProgCount=ProgCount+1;
state=`PROC_DE_LOAD_16_EXTRA_FETCH_SET;
if(opcode_size==0)begin
if(unaligned_access==1)begin
PARAM1 = {external_data_bus[7:0],external_data_bus[15:8]};
ProgCount=ProgCount+1;
state=`PROC_EX_STATE_ENTRY;
end else begin
PARAM1 = {external_data_bus[15:8],CIR[7:0]};
state=`PROC_EX_STATE_ENTRY;
end
end else begin
PARAM1[7:0] = external_data_bus[15:8];
PARAM1[15:8] = external_data_bus[7:0];
ProgCount=ProgCount+1;
state=`PROC_EX_STATE_ENTRY;
if(unaligned_access==1)begin
PARAM1[7:0] = external_data_bus[7:0];
state=`PROC_DE_LOAD_16_EXTRA_FETCH_SET;
end else begin
PARAM1 = {external_data_bus[7:0],external_data_bus[15:8]};
state=`PROC_EX_STATE_ENTRY;
end
end
end
`PROC_DE_LOAD_16_EXTRA_FETCH:begin