litex/verilog/lm32/lm32_decoder.v

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//                         FILE DETAILS
// Project          : LatticeMico32
// File             : lm32_decoder.v
// Title            : Instruction decoder
// Dependencies     : lm32_include.v
// Version          : 6.1.17
//                  : Initial Release
// Version          : 7.0SP2, 3.0
//                  : No Change
// Version          : 3.1
//                  : Support for static branch prediction. Information about
//                  : branch type is generated and passed on to the predictor.
// Version          : 3.2
//                  : No change
// Version          : 3.3
//                  : Renamed port names that conflict with keywords reserved
//                  : in System-Verilog.
// =============================================================================

`include "lm32_include.v"

// Index of opcode field in an instruction
`define LM32_OPCODE_RNG         31:26
`define LM32_OP_RNG             30:26

// Opcodes - Some are only listed as 5 bits as their MSB is a don't care
`define LM32_OPCODE_ADD         5'b01101
`define LM32_OPCODE_AND         5'b01000
`define LM32_OPCODE_ANDHI       6'b011000
`define LM32_OPCODE_B           6'b110000
`define LM32_OPCODE_BI          6'b111000
`define LM32_OPCODE_BE          6'b010001
`define LM32_OPCODE_BG          6'b010010
`define LM32_OPCODE_BGE         6'b010011
`define LM32_OPCODE_BGEU        6'b010100
`define LM32_OPCODE_BGU         6'b010101
`define LM32_OPCODE_BNE         6'b010111
`define LM32_OPCODE_CALL        6'b110110
`define LM32_OPCODE_CALLI       6'b111110
`define LM32_OPCODE_CMPE        5'b11001
`define LM32_OPCODE_CMPG        5'b11010
`define LM32_OPCODE_CMPGE       5'b11011
`define LM32_OPCODE_CMPGEU      5'b11100
`define LM32_OPCODE_CMPGU       5'b11101
`define LM32_OPCODE_CMPNE       5'b11111
`define LM32_OPCODE_DIVU        6'b100011
`define LM32_OPCODE_LB          6'b000100
`define LM32_OPCODE_LBU         6'b010000
`define LM32_OPCODE_LH          6'b000111
`define LM32_OPCODE_LHU         6'b001011
`define LM32_OPCODE_LW          6'b001010
`define LM32_OPCODE_MODU        6'b110001
`define LM32_OPCODE_MUL         5'b00010
`define LM32_OPCODE_NOR         5'b00001
`define LM32_OPCODE_OR          5'b01110
`define LM32_OPCODE_ORHI        6'b011110
`define LM32_OPCODE_RAISE       6'b101011
`define LM32_OPCODE_RCSR        6'b100100
`define LM32_OPCODE_SB          6'b001100
`define LM32_OPCODE_SEXTB       6'b101100
`define LM32_OPCODE_SEXTH       6'b110111
`define LM32_OPCODE_SH          6'b000011
`define LM32_OPCODE_SL          5'b01111
`define LM32_OPCODE_SR          5'b00101
`define LM32_OPCODE_SRU         5'b00000
`define LM32_OPCODE_SUB         6'b110010
`define LM32_OPCODE_SW          6'b010110
`define LM32_OPCODE_USER        6'b110011
`define LM32_OPCODE_WCSR        6'b110100
`define LM32_OPCODE_XNOR        5'b01001
`define LM32_OPCODE_XOR         5'b00110

/////////////////////////////////////////////////////
// Module interface
/////////////////////////////////////////////////////

module lm32_decoder (
    // ----- Inputs -------
    instruction,
    // ----- Outputs -------
    d_result_sel_0,
    d_result_sel_1,        
    x_result_sel_csr,
`ifdef LM32_MC_ARITHMETIC_ENABLED
    x_result_sel_mc_arith,
`endif    
`ifdef LM32_NO_BARREL_SHIFT    
    x_result_sel_shift,
`endif
`ifdef CFG_SIGN_EXTEND_ENABLED
    x_result_sel_sext,
`endif    
    x_result_sel_logic,
`ifdef CFG_USER_ENABLED
    x_result_sel_user,
`endif
    x_result_sel_add,
    m_result_sel_compare,
`ifdef CFG_PL_BARREL_SHIFT_ENABLED
    m_result_sel_shift,  
`endif    
    w_result_sel_load,
`ifdef CFG_PL_MULTIPLY_ENABLED
    w_result_sel_mul,
`endif
    x_bypass_enable,
    m_bypass_enable,
    read_enable_0,
    read_idx_0,
    read_enable_1,
    read_idx_1,
    write_enable,
    write_idx,
    immediate,
    branch_offset,
    load,
    store,
    size,
    sign_extend,
    adder_op,
    logic_op,
`ifdef CFG_PL_BARREL_SHIFT_ENABLED
    direction,
`endif
`ifdef CFG_MC_BARREL_SHIFT_ENABLED
    shift_left,
    shift_right,
`endif
`ifdef CFG_MC_MULTIPLY_ENABLED
    multiply,
`endif
`ifdef CFG_MC_DIVIDE_ENABLED
    divide,
    modulus,
`endif
    branch,
    branch_reg,
    condition,
    bi_conditional,
    bi_unconditional,
`ifdef CFG_DEBUG_ENABLED
    break_opcode,
`endif
    scall,
    eret,
`ifdef CFG_DEBUG_ENABLED
    bret,
`endif
`ifdef CFG_USER_ENABLED
    user_opcode,
`endif
    csr_write_enable
    );

/////////////////////////////////////////////////////
// Inputs
/////////////////////////////////////////////////////

input [`LM32_INSTRUCTION_RNG] instruction;       // Instruction to decode

/////////////////////////////////////////////////////
// Outputs
/////////////////////////////////////////////////////

output [`LM32_D_RESULT_SEL_0_RNG] d_result_sel_0;
reg    [`LM32_D_RESULT_SEL_0_RNG] d_result_sel_0;
output [`LM32_D_RESULT_SEL_1_RNG] d_result_sel_1;
reg    [`LM32_D_RESULT_SEL_1_RNG] d_result_sel_1;
output x_result_sel_csr;
reg    x_result_sel_csr;
`ifdef LM32_MC_ARITHMETIC_ENABLED
output x_result_sel_mc_arith;
reg    x_result_sel_mc_arith;
`endif
`ifdef LM32_NO_BARREL_SHIFT    
output x_result_sel_shift;
reg    x_result_sel_shift;
`endif
`ifdef CFG_SIGN_EXTEND_ENABLED
output x_result_sel_sext;
reg    x_result_sel_sext;
`endif
output x_result_sel_logic;
reg    x_result_sel_logic;
`ifdef CFG_USER_ENABLED
output x_result_sel_user;
reg    x_result_sel_user;
`endif
output x_result_sel_add;
reg    x_result_sel_add;
output m_result_sel_compare;
reg    m_result_sel_compare;
`ifdef CFG_PL_BARREL_SHIFT_ENABLED
output m_result_sel_shift;
reg    m_result_sel_shift;
`endif
output w_result_sel_load;
reg    w_result_sel_load;
`ifdef CFG_PL_MULTIPLY_ENABLED
output w_result_sel_mul;
reg    w_result_sel_mul;
`endif
output x_bypass_enable;
wire   x_bypass_enable;
output m_bypass_enable;
wire   m_bypass_enable;
output read_enable_0;
wire   read_enable_0;
output [`LM32_REG_IDX_RNG] read_idx_0;
wire   [`LM32_REG_IDX_RNG] read_idx_0;
output read_enable_1;
wire   read_enable_1;
output [`LM32_REG_IDX_RNG] read_idx_1;
wire   [`LM32_REG_IDX_RNG] read_idx_1;
output write_enable;
wire   write_enable;
output [`LM32_REG_IDX_RNG] write_idx;
wire   [`LM32_REG_IDX_RNG] write_idx;
output [`LM32_WORD_RNG] immediate;
wire   [`LM32_WORD_RNG] immediate;
output [`LM32_PC_RNG] branch_offset;
wire   [`LM32_PC_RNG] branch_offset;
output load;
wire   load;
output store;
wire   store;
output [`LM32_SIZE_RNG] size;
wire   [`LM32_SIZE_RNG] size;
output sign_extend;
wire   sign_extend;
output adder_op;
wire   adder_op;
output [`LM32_LOGIC_OP_RNG] logic_op;
wire   [`LM32_LOGIC_OP_RNG] logic_op;
`ifdef CFG_PL_BARREL_SHIFT_ENABLED
output direction;
wire   direction;
`endif
`ifdef CFG_MC_BARREL_SHIFT_ENABLED
output shift_left;
wire   shift_left;
output shift_right;
wire   shift_right;
`endif
`ifdef CFG_MC_MULTIPLY_ENABLED
output multiply;
wire   multiply;
`endif
`ifdef CFG_MC_DIVIDE_ENABLED
output divide;
wire   divide;
output modulus;
wire   modulus;
`endif
output branch;
wire   branch;
output branch_reg;
wire   branch_reg;
output [`LM32_CONDITION_RNG] condition;
wire   [`LM32_CONDITION_RNG] condition;
output bi_conditional;
wire bi_conditional;
output bi_unconditional;
wire bi_unconditional;
`ifdef CFG_DEBUG_ENABLED
output break_opcode;
wire   break_opcode;
`endif
output scall;
wire   scall;
output eret;
wire   eret;
`ifdef CFG_DEBUG_ENABLED
output bret;
wire   bret;
`endif
`ifdef CFG_USER_ENABLED
output [`LM32_USER_OPCODE_RNG] user_opcode;
wire   [`LM32_USER_OPCODE_RNG] user_opcode;
`endif
output csr_write_enable;
wire   csr_write_enable;

/////////////////////////////////////////////////////
// Internal nets and registers 
/////////////////////////////////////////////////////

wire [`LM32_WORD_RNG] extended_immediate;       // Zero or sign extended immediate
wire [`LM32_WORD_RNG] high_immediate;           // Immediate as high 16 bits
wire [`LM32_WORD_RNG] call_immediate;           // Call immediate
wire [`LM32_WORD_RNG] branch_immediate;         // Conditional branch immediate
wire sign_extend_immediate;                     // Whether the immediate should be sign extended (`TRUE) or zero extended (`FALSE)
wire select_high_immediate;                     // Whether to select the high immediate  
wire select_call_immediate;                     // Whether to select the call immediate 

/////////////////////////////////////////////////////
// Functions
/////////////////////////////////////////////////////

`include "lm32_functions.v"

/////////////////////////////////////////////////////
// Combinational logic
/////////////////////////////////////////////////////

// Determine opcode
assign op_add    = instruction[`LM32_OP_RNG] == `LM32_OPCODE_ADD;
assign op_and    = instruction[`LM32_OP_RNG] == `LM32_OPCODE_AND;
assign op_andhi  = instruction[`LM32_OPCODE_RNG] == `LM32_OPCODE_ANDHI;
assign op_b      = instruction[`LM32_OPCODE_RNG] == `LM32_OPCODE_B;
assign op_bi     = instruction[`LM32_OPCODE_RNG] == `LM32_OPCODE_BI;
assign op_be     = instruction[`LM32_OPCODE_RNG] == `LM32_OPCODE_BE;
assign op_bg     = instruction[`LM32_OPCODE_RNG] == `LM32_OPCODE_BG;
assign op_bge    = instruction[`LM32_OPCODE_RNG] == `LM32_OPCODE_BGE;
assign op_bgeu   = instruction[`LM32_OPCODE_RNG] == `LM32_OPCODE_BGEU;
assign op_bgu    = instruction[`LM32_OPCODE_RNG] == `LM32_OPCODE_BGU;
assign op_bne    = instruction[`LM32_OPCODE_RNG] == `LM32_OPCODE_BNE;
assign op_call   = instruction[`LM32_OPCODE_RNG] == `LM32_OPCODE_CALL;
assign op_calli  = instruction[`LM32_OPCODE_RNG] == `LM32_OPCODE_CALLI;
assign op_cmpe   = instruction[`LM32_OP_RNG] == `LM32_OPCODE_CMPE;
assign op_cmpg   = instruction[`LM32_OP_RNG] == `LM32_OPCODE_CMPG;
assign op_cmpge  = instruction[`LM32_OP_RNG] == `LM32_OPCODE_CMPGE;
assign op_cmpgeu = instruction[`LM32_OP_RNG] == `LM32_OPCODE_CMPGEU;
assign op_cmpgu  = instruction[`LM32_OP_RNG] == `LM32_OPCODE_CMPGU;
assign op_cmpne  = instruction[`LM32_OP_RNG] == `LM32_OPCODE_CMPNE;
`ifdef CFG_MC_DIVIDE_ENABLED
assign op_divu   = instruction[`LM32_OPCODE_RNG] == `LM32_OPCODE_DIVU;
`endif
assign op_lb     = instruction[`LM32_OPCODE_RNG] == `LM32_OPCODE_LB;
assign op_lbu    = instruction[`LM32_OPCODE_RNG] == `LM32_OPCODE_LBU;
assign op_lh     = instruction[`LM32_OPCODE_RNG] == `LM32_OPCODE_LH;
assign op_lhu    = instruction[`LM32_OPCODE_RNG] == `LM32_OPCODE_LHU;
assign op_lw     = instruction[`LM32_OPCODE_RNG] == `LM32_OPCODE_LW;
`ifdef CFG_MC_DIVIDE_ENABLED
assign op_modu   = instruction[`LM32_OPCODE_RNG] == `LM32_OPCODE_MODU;
`endif
`ifdef LM32_MULTIPLY_ENABLED
assign op_mul    = instruction[`LM32_OP_RNG] == `LM32_OPCODE_MUL;
`endif
assign op_nor    = instruction[`LM32_OP_RNG] == `LM32_OPCODE_NOR;
assign op_or     = instruction[`LM32_OP_RNG] == `LM32_OPCODE_OR;
assign op_orhi   = instruction[`LM32_OPCODE_RNG] == `LM32_OPCODE_ORHI;
assign op_raise  = instruction[`LM32_OPCODE_RNG] == `LM32_OPCODE_RAISE;
assign op_rcsr   = instruction[`LM32_OPCODE_RNG] == `LM32_OPCODE_RCSR;
assign op_sb     = instruction[`LM32_OPCODE_RNG] == `LM32_OPCODE_SB;
`ifdef CFG_SIGN_EXTEND_ENABLED
assign op_sextb  = instruction[`LM32_OPCODE_RNG] == `LM32_OPCODE_SEXTB;
assign op_sexth  = instruction[`LM32_OPCODE_RNG] == `LM32_OPCODE_SEXTH;
`endif
assign op_sh     = instruction[`LM32_OPCODE_RNG] == `LM32_OPCODE_SH;
`ifdef LM32_BARREL_SHIFT_ENABLED
assign op_sl     = instruction[`LM32_OP_RNG] == `LM32_OPCODE_SL;      
`endif
assign op_sr     = instruction[`LM32_OP_RNG] == `LM32_OPCODE_SR;
assign op_sru    = instruction[`LM32_OP_RNG] == `LM32_OPCODE_SRU;
assign op_sub    = instruction[`LM32_OPCODE_RNG] == `LM32_OPCODE_SUB;
assign op_sw     = instruction[`LM32_OPCODE_RNG] == `LM32_OPCODE_SW;
assign op_user   = instruction[`LM32_OPCODE_RNG] == `LM32_OPCODE_USER;
assign op_wcsr   = instruction[`LM32_OPCODE_RNG] == `LM32_OPCODE_WCSR;
assign op_xnor   = instruction[`LM32_OP_RNG] == `LM32_OPCODE_XNOR;
assign op_xor    = instruction[`LM32_OP_RNG] == `LM32_OPCODE_XOR;

// Group opcodes by function
assign arith = op_add | op_sub;
assign logical = op_and | op_andhi | op_nor | op_or | op_orhi | op_xor | op_xnor;
assign cmp = op_cmpe | op_cmpg | op_cmpge | op_cmpgeu | op_cmpgu | op_cmpne;
assign bi_conditional = op_be | op_bg | op_bge | op_bgeu  | op_bgu | op_bne;
assign bi_unconditional = op_bi;
assign bra = op_b | bi_unconditional | bi_conditional;
assign call = op_call | op_calli;
`ifdef LM32_BARREL_SHIFT_ENABLED
assign shift = op_sl | op_sr | op_sru;
`endif
`ifdef LM32_NO_BARREL_SHIFT
assign shift = op_sr | op_sru;
`endif
`ifdef CFG_MC_BARREL_SHIFT_ENABLED
assign shift_left = op_sl;
assign shift_right = op_sr | op_sru;
`endif
`ifdef CFG_SIGN_EXTEND_ENABLED
assign sext = op_sextb | op_sexth;
`endif
`ifdef LM32_MULTIPLY_ENABLED
assign multiply = op_mul;
`endif
`ifdef CFG_MC_DIVIDE_ENABLED
assign divide = op_divu; 
assign modulus = op_modu;
`endif
assign load = op_lb | op_lbu | op_lh | op_lhu | op_lw;
assign store = op_sb | op_sh | op_sw;

// Select pipeline multiplexor controls
always @(*)
begin
    // D stage
    if (call) 
        d_result_sel_0 = `LM32_D_RESULT_SEL_0_NEXT_PC;
    else 
        d_result_sel_0 = `LM32_D_RESULT_SEL_0_REG_0;
    if (call) 
        d_result_sel_1 = `LM32_D_RESULT_SEL_1_ZERO;         
    else if ((instruction[31] == 1'b0) && !bra) 
        d_result_sel_1 = `LM32_D_RESULT_SEL_1_IMMEDIATE;
    else
        d_result_sel_1 = `LM32_D_RESULT_SEL_1_REG_1; 
    // X stage
    x_result_sel_csr = `FALSE;
`ifdef LM32_MC_ARITHMETIC_ENABLED
    x_result_sel_mc_arith = `FALSE;
`endif
`ifdef LM32_NO_BARREL_SHIFT
    x_result_sel_shift = `FALSE;
`endif
`ifdef CFG_SIGN_EXTEND_ENABLED
    x_result_sel_sext = `FALSE;
`endif
    x_result_sel_logic = `FALSE;
`ifdef CFG_USER_ENABLED        
    x_result_sel_user = `FALSE;
`endif
    x_result_sel_add = `FALSE;
    if (op_rcsr)
        x_result_sel_csr = `TRUE;
`ifdef LM32_MC_ARITHMETIC_ENABLED    
`ifdef CFG_MC_BARREL_SHIFT_ENABLED
    else if (shift_left | shift_right) 
        x_result_sel_mc_arith = `TRUE;
`endif
`ifdef CFG_MC_DIVIDE_ENABLED
    else if (divide | modulus)
        x_result_sel_mc_arith = `TRUE;        
`endif
`ifdef CFG_MC_MULTIPLY_ENABLED
    else if (multiply)
        x_result_sel_mc_arith = `TRUE;            
`endif
`endif
`ifdef LM32_NO_BARREL_SHIFT
    else if (shift)
        x_result_sel_shift = `TRUE;        
`endif
`ifdef CFG_SIGN_EXTEND_ENABLED
    else if (sext)
        x_result_sel_sext = `TRUE;
`endif        
    else if (logical) 
        x_result_sel_logic = `TRUE;
`ifdef CFG_USER_ENABLED        
    else if (op_user)
        x_result_sel_user = `TRUE;
`endif
    else 
        x_result_sel_add = `TRUE;        
    
    // M stage

    m_result_sel_compare = cmp;
`ifdef CFG_PL_BARREL_SHIFT_ENABLED
    m_result_sel_shift = shift;
`endif

    // W stage
    w_result_sel_load = load;
`ifdef CFG_PL_MULTIPLY_ENABLED
    w_result_sel_mul = op_mul; 
`endif
end

// Set if result is valid at end of X stage
assign x_bypass_enable =  arith 
                        | logical
`ifdef CFG_MC_BARREL_SHIFT_ENABLED
                        | shift_left
                        | shift_right
`endif                        
`ifdef CFG_MC_MULTIPLY_ENABLED
                        | multiply
`endif
`ifdef CFG_MC_DIVIDE_ENABLED
                        | divide
                        | modulus
`endif
`ifdef LM32_NO_BARREL_SHIFT
                        | shift
`endif                  
`ifdef CFG_SIGN_EXTEND_ENABLED
                        | sext 
`endif                        
`ifdef CFG_USER_ENABLED
                        | op_user
`endif
                        | op_rcsr
                        ;
// Set if result is valid at end of M stage                        
assign m_bypass_enable = x_bypass_enable 
`ifdef CFG_PL_BARREL_SHIFT_ENABLED
                        | shift
`endif
                        | cmp
                        ;
// Register file read port 0                        
assign read_enable_0 = ~(op_bi | op_calli);
assign read_idx_0 = instruction[25:21];
// Register file read port 1 
assign read_enable_1 = ~(op_bi | op_calli | load);
assign read_idx_1 = instruction[20:16];
// Register file write port
assign write_enable = ~(bra | op_raise | store | op_wcsr);
assign write_idx = call
                    ? 5'd29
                    : instruction[31] == 1'b0 
                        ? instruction[20:16] 
                        : instruction[15:11];
                        
// Size of load/stores                        
assign size = instruction[27:26];
// Whether to sign or zero extend
assign sign_extend = instruction[28];                      
// Set adder_op to 1 to perform a subtraction
assign adder_op = op_sub | op_cmpe | op_cmpg | op_cmpge | op_cmpgeu | op_cmpgu | op_cmpne | bra;
// Logic operation (and, or, etc)
assign logic_op = instruction[29:26];
`ifdef CFG_PL_BARREL_SHIFT_ENABLED
// Shift direction
assign direction = instruction[29];
`endif
// Control flow microcodes
assign branch = bra | call;
assign branch_reg = op_call | op_b;
assign condition = instruction[28:26];      
`ifdef CFG_DEBUG_ENABLED
assign break_opcode = op_raise & ~instruction[2];
`endif
assign scall = op_raise & instruction[2];
assign eret = op_b & (instruction[25:21] == 5'd30);
`ifdef CFG_DEBUG_ENABLED
assign bret = op_b & (instruction[25:21] == 5'd31);
`endif
`ifdef CFG_USER_ENABLED
// Extract user opcode
assign user_opcode = instruction[10:0];
`endif
// CSR read/write
assign csr_write_enable = op_wcsr;

// Extract immediate from instruction

assign sign_extend_immediate = ~(op_and | op_cmpgeu | op_cmpgu | op_nor | op_or | op_xnor | op_xor);
assign select_high_immediate = op_andhi | op_orhi;
assign select_call_immediate = instruction[31];

assign high_immediate = {instruction[15:0], 16'h0000};
assign extended_immediate = {{16{sign_extend_immediate & instruction[15]}}, instruction[15:0]};
assign call_immediate = {{6{instruction[25]}}, instruction[25:0]};
assign branch_immediate = {{16{instruction[15]}}, instruction[15:0]};

assign immediate = select_high_immediate == `TRUE 
                        ? high_immediate 
                        : extended_immediate;
   
assign branch_offset = select_call_immediate == `TRUE   
                        ? call_immediate
                        : branch_immediate;
    
endmodule