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/* SXP (Simple Extensible Pipeline) Core

 *

 * Architecture - Sam Gladstone

 *

 */

// `define SYNC_REG

module sxp

                (clk,

                 reset_b,

                 mem_inst,              // Instruction ram read data

                 spqa,                  // scratch pad memory port A output (load data)

                 ext_ra,                // extension register a

                 ext_rb,                // extension register b

                 ext_result,            // extension bus result data

                 ext_cvnz,              // extension ALU flag result

                 halt,                  // halts operation of processor

                 int_req,               // interupt request

                 int_num,               // interupt number for request

                 int_rdy,               // interupt controller ready for interupt

                 int_srv_req,           // signal that interupt is being serviced

                 int_srv_num,           // interupt number being serviced

                 ext_alu_a,             // reg A for ext ALU

                 ext_alu_b,             // reg B for ext ALU

                 ext_inst,              // copy of 32 bit instruction for extension architecture

                 ext_inst_vld,          // test ext architecture that instruction is valid

                 ext_we,                // extension bus write enable (dest)

                 extr_addr,             // ext bus address to read from (qra)

                 extw_data,             // data to write to extension bus (dest)

                 extw_addr,             // ext address to write to

                 spl_addr,              // scratch pad memory (Port A) load address (from reg file A)

                 spw_addr,              // scratch pad memory (Port B) write address (from ALU passthough)

                 spw_we,                // scretch pad memory (Port B) write enable (from wb source section)

                 spw_data,              // scratch pad memory (Port B) write data (from ALU passthrough) 

                 mem_pc);               // Program Counter Address

parameter RF_WIDTH = 4;

parameter RF_SIZE  = 16;

input clk;

input reset_b;

input [31:0] mem_inst;

input [31:0] spqa;

input [31:0] ext_ra;

input [31:0] ext_rb;

input [31:0] ext_result;

input [3:0] ext_cvnz;

input halt;

input int_req;

input [15:0] int_num;

output int_rdy;

output int_srv_req;

output [15:0] int_srv_num;

output [31:0] ext_alu_a;

output [31:0] ext_alu_b;

output  ext_we;

reg     ext_we;

output [31:0] extr_addr;

output [31:0] extw_data;

output [31:0] extw_addr;

output [31:0] spl_addr;

output [31:0] spw_addr;

output spw_we;

reg spw_we;

output [31:0] spw_data;

output [31:0] mem_pc;

output [31:0] ext_inst;

output ext_inst_vld;

// Scratch pad signal and regs

reg [31:0] spl_addr_3;

reg [31:0] spl_addr_3_wb;

reg [31:0] spl_data_3_wb;

reg spl_we_3_wb;

reg [31:0] spl_data;

// Internal Wires

wire stall_1_2;                 // signal to stall pipelines 1 and 2

reg [31:0] wb_data;              // write back registered data

// Fetch interface wires

wire  set_pc;

wire flush_pipeline;            // signal to invalidate all pipelines

wire stall_fetch;               // stall for fetch module

// Regf interface wires

reg wec;                        // write enable for RF write to port C

wire [31:0] qra;         // regfile output for A

wire [31:0] qrb;         // regfile output for B

// ALU interface wires 

wire [3:0] cvnz_a;               // base ALU A flags

wire [3:0] cvnz_b;               // base ALU B flags

wire [31:0] ya;                  // A result from ALU 

wire [31:0] yb;                  // B result from ALU 

// Pipeline #1 wires and regs

wire stall_1;                   // stall 1st pipeline (fetch)

wire [31:0] pcn_1;               // Program Counter + 1

wire inst_vld_1;                // instruction valid from pipeline 1

wire [31:0] inst_1;              // 32 bit instruction from pipeline 1

wire [1:0] dest_cfg_1;           // destination configuration from pipeline 1

wire [RF_WIDTH-1:0] dest_addr_1;// destination address for reg file writeback

wire [2:0] src_cfg_1;            // ALU source configuration from pipeline 1

wire [2:0] alu_cfg_1;            // ALU configuration from pipeline 1

wire [3:0] wb_cfg_1;             // write back source configuration from pipeline 1

wire [RF_WIDTH-1:0] addra_1;     // address for reg file A from pipeline 1

wire [RF_WIDTH-1:0] addrb_1;     // address for reg file B from pipeline 1

wire [RF_WIDTH-1:0] addrc_1;     // address for reg file write C from pipeline 1

wire [15:0] imm_1;               // immediate value from pipeline 1

reg dest_en_1;                  // destination register enable for scoreboarding

reg a_en;                       // A reg is enable for reg file and scoreboarding

reg b_en;                       // B reg is enable for reg file and scoreboarding

wire cond_jump_1;               // lsb of instruction is used for conditional reg jumps

wire jz_1;                      // jump if zero instruction (false is jump if not zero) 

wire jal_1;                     // jump and link from pipeline 1

// Pipeline #2 (from memory latency) wires and regs

wire stall_2;                   // stall 2nd pipeline

reg  inst_vld_2;                // instruction valid signal from pipeline 2

reg  [1:0] dest_cfg_2;           // destination configuration from pipeline 2

reg  [RF_WIDTH-1:0] dest_addr_2;// destination address for RF write from pipeline 2

reg  [2:0] src_cfg_2;            // ALU source configuration from pipeline 2

reg  [2:0] alu_cfg_2;            // ALU configuration from pipeline 2

reg  [3:0] wb_cfg_2;             // write back source configuration from pipeline 2

reg  [15:0] imm_2;               // immediate value from pipeline 2

reg  [31:0] pcn_2;               // next PC address from pipeline 2 

reg  [31:0] a_2;         // Selected ALU A from pipeline 2

reg  [31:0] b_2;         // Selected ALU B from pipeline 2

reg  cond_jump_2;               // Conditional jump from pipeline 2

reg  jz_2;                      // jump if zero instruction (false is jump if not zero) 

reg  jal_2;                     // jump and link from pipeline 2

// Pipeline #3 (for ALU setup) wires and regs

reg [31:0] r_qra;                // load stall protection register

wire stall_3;                   // stall 3rd pipeline

reg  inst_vld_3;                // instruction valid signal from pipeline 3

reg  [1:0] dest_cfg_3;           // destination configuration from pipeline 3

reg  [RF_WIDTH-1:0] dest_addr_3;// destination address for RF write from pipeline 3

reg  [2:0] alu_cfg_3;            // ALU configuration from pipeline 3

reg  [3:0] wb_cfg_3;             // write back source configuration from pipeline 3

reg  [31:0] pcn_3;               // next program counter value for pipeline 3

reg  [31:0] a_3;         // ALU input A from pipeline 3

reg  [31:0] b_3;         // ALU input B from pipeline 3

reg  cond_jump_3;               // Conditional jump from pipeline 3

reg  jz_3;                      // jump if zero instruction (false is jump if not zero) 

reg  jal_3;                     // jump and link from pipeline 3

// Pipeline #4 (WB and destination logic) wires and regs

wire stall_4;                   // stall 4th pipeline

reg  set_pc_4;                  // preliminary signal to set pc in pipeline 4

reg  inst_vld_4;                // instruction valid signal from pipeline 4

reg  [1:0] dest_cfg_4;           // destination configuration from pipeline 4

reg  [RF_WIDTH-1:0] dest_addr_4;// destination address for RF write from pipeline 4

reg  [3:0] wb_cfg_4;             // write back source configuration from pipeline 4

reg  [31:0] spqa_4;              // scratch pad output from pipeline 4 

reg  [31:0] ya_4;                // used for scratch pad memory stores

reg  [31:0] yb_4;                // used for scratch pad memory stores

reg  [31:0] ext_result_4;        // ext ALU result from pipeline 4

reg  [31:0] pcn_4;               // next program counter value for pipeline 4

reg  [3:0] ext_cvnz_4;           // ext ALU flags from pipeline 4

reg  [3:0] cvnz_a_4;             // ALU a result from pipeline 4

reg  [3:0] cvnz_b_4;             // ALU b result from pipeline 4

wire [RF_WIDTH-1:0] addrc_wb;    // connects dest_addr_4 to reg file write port C

reg  cond_jump_4;               // Conditional jump from pipeline 4

reg  jz_4;                      // jump if zero instruction (false is jump if not zero) 

reg  jal_4;                     // jump and link from pipeline 4

wire [31:0] regc_data;           // data to be written to port C (reg file)

// stall signal handling

assign stall_1 = stall_1_2 || halt;

assign stall_2 = stall_1_2 || halt;

assign stall_3 = halt;

assign stall_4 = halt;

// Interupt signals

wire idle;

wire jal_req;

wire safe_switch;

wire nop_detect;

wire int_jal_req;

// Processor Interupt controller

int_cont i_int_cont(

                .clk(clk),                      // system clock

                .reset_b(reset_b),              // system reset

                .halt(halt),                    // processor halt signal

                .int_req(int_req),              // signal that an interupt is requested

                .int_num(int_num),              // interupt number that is being requested

                .safe_switch(safe_switch),      // signal that processor is safe to switch

                .nop_detect(nop_detect),        // signal that the processor just executed a NOP instruction

                .int_rdy(int_rdy),              // 1 when int req will be serviced when requested

                .idle(idle),                    // signal to idle processor;

                .jal_req(jal_req),              // signal to fetch to insert the JAL instruction

                .int_srv_req(int_srv_req),      // signal that the interupt was serviced

                .int_srv_num(int_srv_num));     // interupt number that was serviced

// Fetch Section

fetch   i_fetch (

                 .clk(clk),                     // system clock

                 .reset_b(reset_b),             // system reset

                 .stall(stall_1),               // stall for fetch

                 .set_pc(set_pc),               // signal to set the program counter

                 .pc_init(wb_data),             // value to set the program counter to 

                 .mem_inst(mem_inst),           // instruction that was read from memory

                 .idle(idle),                   // idle fetch process 

                 .jal_req(jal_req),             // interupt jump and link request;

                 .int_srv_num(int_srv_num),     // interupt number for JAL

                 .int_jal_req(int_jal_req),     // interupt JAL signal request

                 .mem_pc(mem_pc),               // address to get from memory 

                 .pcn(pcn_1),                   // Next PC address

                 .flush_pipeline(flush_pipeline),       // Invalidate all pipelines (done during jumps)

                 .inst_vld(inst_vld_1),         // instruction valid flag

                 .inst(inst_1));                // instruction to be sent to pipeline

assign ext_inst = inst_1;

assign ext_inst_vld = inst_vld_1;

// Need to begin breaking out wire meaning for the next section

assign dest_cfg_1 = inst_1[31:30];

assign src_cfg_1 = inst_1[29:27];

assign alu_cfg_1 = inst_1[26:24];

assign wb_cfg_1 = inst_1[23:20];

assign dest_addr_1 = inst_1[19:16];

assign addra_1 = (src_cfg_1 == 3'b001) ? dest_addr_1 : inst_1[15:12];

assign addrb_1 = inst_1[11:8];

assign imm_1 = inst_1[15:0];

assign cond_jump_1 = inst_1[0];

assign jz_1 = inst_1[1];

assign jal_1 = (!src_cfg_1[0] && !src_cfg_1[2]) ? inst_1[2] : int_jal_req;

// This protects jal against imm and ext type sources

// ----------------------- Reg File Section ------------------------

always @(src_cfg_1 or inst_vld_1 or dest_cfg_1)

  begin

    if (inst_vld_1)

      begin

        dest_en_1 = !dest_cfg_1;                // Destination is register

        case (src_cfg_1)

          3'b 000 : begin

                      a_en = 1'b 1;

                      b_en = 1'b 1;

                    end

          3'b 001 : begin

                      a_en = 1'b 1;

                      b_en = 1'b 0;

                    end

          3'b 010 : begin

                      a_en = 1'b 0;

                      b_en = 1'b 1;

                    end

          3'b 011 : begin

                      a_en = 1'b 0;

                      b_en = 1'b 0;

                    end

          3'b 100 : begin

                      a_en = 1'b 1;

                      b_en = 1'b 0;

                    end

          3'b 101 : begin

                      a_en = 1'b 0;

                      b_en = 1'b 1;

                    end

          3'b 110 : begin

                      a_en = 1'b 0;

                      b_en = 1'b 0;

                    end

          3'b 111 : begin

                      a_en = 1'b 0;

                      b_en = 1'b 0;

                    end

         endcase

      end

    else

      begin

        a_en = 1'b 0;

        b_en = 1'b 0;

        dest_en_1 = 1'b 0;

      end

  end

`ifdef SYNC_REG

sync_regf #(4,16) i_regf (

                .clk(clk),                      // system clock

                .reset_b(reset_b),              // power on reset

                .halt(halt),                    // system wide halt

                .addra(addra_1),                // Port A read address 

                .a_en(a_en),                    // Port A read enable

                .addrb(addrb_1),                // Port B read address 

                .b_en(b_en),                    // Port B read enable 

                .addrc(addrc_wb),               // Port C write address 

                .dc(regc_data),                 // Port C write data 

                .wec(wec),                      // Port C write enable 

                .qra(qra),                      // Port A registered output data        

                .qrb(qrb));                     // Port B registered output data        

`else

mem_regf #(4,16) i_regf (

                .clk(clk),                      // system clock

                .reset_b(reset_b),              // power on reset

                .halt(halt),                    // system wide halt

                .addra(addra_1),                // Port A read address 

                .a_en(a_en),                    // Port A read enable

                .addrb(addrb_1),                // Port B read address 

                .b_en(b_en),                    // Port B read enable 

                .addrc(addrc_wb),               // Port C write address 

                .dc(regc_data),                 // Port C write data 

                .wec(wec),                      // Port C write enable 

                .qra(qra),                      // Port A registered output data        

                .qrb(qrb));                     // Port B registered output data        

`endif

regf_status #(4,16) i_regf_status(

                .clk(clk),                      // system clock

                .reset_b(reset_b),              // power on reset

                .stall(stall_1_2),              // stall in pipeline 1 and 2 

                .halt(halt),                    // system wide stall signal

                .dest_en(dest_en_1),            // instr has dest register (en scoreboarding)

                .dest_addr(dest_addr_1),        // destination address from instruction

                .wec(wec),                      // port C write back request

                .addrc(addrc_wb),               // port C write back address

                .addra(addra_1),                // reg file address reg A (source 1)

                .addrb(addrb_1),                // reg file address reg B (source 2)

                .a_en(a_en),                    // Reg A is enabled in instruction

                .b_en(b_en),                    // Reg B is enabled in instruction

                .flush_pipeline(flush_pipeline),// Reinitialize status after pipeline flush

                .safe_switch(safe_switch),    // safe to context switch or interupt;

                .stall_regf(stall_1_2));    // stall the reg file and modules prior

`ifdef SYNC_REG

always @(inst_vld_1 or stall_1_2 or  dest_cfg_1 or dest_addr_1 or src_cfg_1 or

         alu_cfg_1 or wb_cfg_1 or imm_1 or pcn_1 or cond_jump_1 or b_en or

         jz_1 or jal_1)

  begin

    inst_vld_2 = (stall_1_2 || flush_pipeline) ? 1'b 0 : inst_vld_1;             // Breaks the pipeline when reg needs to be stalled

    dest_cfg_2 = dest_cfg_1;

    dest_addr_2 = dest_addr_1;

    src_cfg_2 = src_cfg_1;

    alu_cfg_2 = alu_cfg_1;

    wb_cfg_2 = wb_cfg_1;

    imm_2 = imm_1;

    pcn_2 = pcn_1;

    cond_jump_2 = cond_jump_1 & b_en;                           // not valid unles b is enabled for read

    jz_2 = jz_1;

    jal_2 = jal_1;

  end

`else

// There is a pipeline inside the memory for the regfile 

// Need to account for memory pipeline to keep everything alligned 

always @(posedge clk or negedge reset_b)

  begin

    if (!reset_b)

      begin

        inst_vld_2 <= 'b 0;

        dest_cfg_2 <= 'b 0;

        dest_addr_2 <= 'b 0;

        src_cfg_2 <= 'b 0;

        alu_cfg_2 <= 'b 0;

        wb_cfg_2 <= 'b 0;

        imm_2 <= 'b 0;

        pcn_2 <= 'b 0;

        cond_jump_2 <= 'b 0;

        jz_2 <= 'b 0;

        jal_2 <= 'b 0;

      end

    else

      if (flush_pipeline)

        inst_vld_2 <= 'b 0;

      else

        if (!halt)

          begin

            inst_vld_2 <= (stall_1_2) ? 1'b 0 : inst_vld_1;      // Breaks the pipeline when reg needs to be stalled

            if (inst_vld_1 && !stall_1_2)                       // This will save some power by causing unecessary toggling

              begin

                dest_cfg_2 <= dest_cfg_1;

                dest_addr_2 <= dest_addr_1;

                src_cfg_2 <= src_cfg_1;

                alu_cfg_2 <= alu_cfg_1;

                wb_cfg_2 <= wb_cfg_1;

                imm_2 <= imm_1;

                pcn_2 <= pcn_1;

                cond_jump_2 <= cond_jump_1 & b_en;      // not valid unles b is enabled for read

                jz_2 <= jz_1;

                jal_2 <= jal_1;

              end

          end

  end

`endif

// Not sure if protection is needed or which stall (2 or 3) to use? 

// Load Stall protection circuit.

always @(posedge clk or negedge reset_b)

  begin

    if (!reset_b)

      r_qra <= 'b 0;

    else

      if (!halt)

        r_qra <= qra;

  end

assign spl_addr = (halt) ? r_qra : qra; // scratch pad memory load address from Reg A in pipeline 2

assign extr_addr = (halt) ? r_qra : qra; // ext bus load address from Reg A in pipeline 2

// End of memory load with stall protecttion

// Ready to select source data for ALU

always @(src_cfg_2 or qra or qrb or ext_ra or ext_rb or pcn_2 or imm_2)

  begin

    case (src_cfg_2)

      3'b 000 : begin

                  a_2 = qra;

                  b_2 = qrb;

                end

      3'b 001 : begin

                  a_2 = qra;

                  b_2 = {16'b 0, imm_2};

                end

      3'b 010 : begin

                  a_2 = pcn_2;

                  b_2 = qrb;

                end

      3'b 011 : begin

                  a_2 = pcn_2;

                  b_2 = {16'b 0, imm_2};

                end

      3'b 100 : begin

                  a_2 = qra;

                  b_2 = ext_rb;

                end

      3'b 101 : begin

                  a_2 = ext_ra;

                  b_2 = qrb;

                end

      3'b 110 : begin

                  a_2 = ext_ra;

                  b_2 = {16'b 0, imm_2};

                end

      3'b 111 : begin

                  a_2 = ext_ra;

                  b_2 = ext_rb;

                end

    endcase

  end

// --------- 3rd pipeline (ALU signals) ----------- 

always @(posedge clk or negedge reset_b)

  begin

    if (!reset_b)

      begin

        inst_vld_3 <= 'b 0;

        a_3 <= 'b 0;

        b_3 <= 'b 0;

        dest_cfg_3 <= 'b 0;

        dest_addr_3 <= 'b 0;

        alu_cfg_3 <= 'b 0;

        wb_cfg_3 <= 'b 0;

        pcn_3 <= 'b 0;

        cond_jump_3 <= 'b 0;

        jz_3 <= 'b 0;

        jal_3 <= 'b 0;

        spl_addr_3 <= 'b 0;

        spl_addr_3_wb <= 'b 0;

        spl_data_3_wb <= 'b 0;

        spl_we_3_wb <= 'b 0;

      end

    else

      if (flush_pipeline)               // flush pipeline take priority

        inst_vld_3 <= 'b 0;

      else

        if (!stall_3)

          begin

            inst_vld_3 <= inst_vld_2;

            if (inst_vld_2)             // For power savings

              begin

                a_3 <= a_2;

                b_3 <= b_2;

                dest_cfg_3 <= dest_cfg_2;

                dest_addr_3 <= dest_addr_2;

                alu_cfg_3 <= alu_cfg_2;

                wb_cfg_3 <= wb_cfg_2;

                pcn_3 <= pcn_2;

                cond_jump_3 <= cond_jump_2;

                jz_3 <= jz_2;

                jal_3 <= jal_2;

                spl_addr_3 <= spl_addr;

                spl_addr_3_wb <= spw_addr;

                spl_data_3_wb <= spw_data;

                spl_we_3_wb <= spw_we;

              end

          end

  end

assign ext_alu_a = a_3;                 // allow ext ALU to see the inputs

assign ext_alu_b = b_3;                 // allow ext ALU to see the inputs

alu      i_alu (

                .opcode(alu_cfg_3),     // alu function select

                .a(a_3),                // a operand

                .b(b_3),                // b operand

                .cin(1'b 0),             // carry input          (How do we handle this?)

                .ya(ya),                // data output

                .yb(yb),                // data output

                .cvnz_a(cvnz_a),        // flag output for a

                .cvnz_b(cvnz_b)         // flag output for b

                );

always @(spqa or spw_we or spl_addr_3 or spw_addr or spw_data or spl_we_3_wb or spl_addr_3_wb or spl_data_3_wb)

  begin

    if ((spl_addr_3 == spw_addr) && spw_we)

      spl_data = spw_data;

    else

      if ((spl_addr_3 == spl_addr_3_wb) && spl_we_3_wb)

        spl_data = spl_data_3_wb;

      else

        spl_data = spqa;

  end

// New Pipeline 4 starts here

always @(posedge clk or negedge reset_b)

  begin

    if (!reset_b)

      begin

        ext_result_4 <= 'b 0;

        ext_cvnz_4 <= 'b 0;

        spqa_4 <= 'b 0;

        ya_4 <= 'b 0;

        cvnz_a_4 <= 'b 0;

        yb_4 <= 'b 0;

        cvnz_b_4 <= 'b 0;

        inst_vld_4 <= 'b 0;

        wb_cfg_4 <= 'b 0;

        dest_addr_4 <= 'b 0;

        dest_cfg_4 <= 'b 0;

        pcn_4 <= 'b 0;

        cond_jump_4 <= 'b 0;

        jz_4 <= 'b 0;

        jal_4 <= 'b 0;

      end

    else

      if (flush_pipeline)                       // Pipeline flush takes priority over stall

        inst_vld_4 <= 'b 0;

      else

        if (!stall_4)

          begin

            inst_vld_4 <= inst_vld_3;

            if (inst_vld_3)                     // For power savings

              begin

                ext_result_4 <= ext_result;

                ext_cvnz_4 <= ext_cvnz;

                spqa_4 <= spl_data;

                ya_4 <= ya;

                cvnz_a_4 <= cvnz_a;

                yb_4 <= yb;

                cvnz_b_4 <= cvnz_b;

                inst_vld_4 <= inst_vld_3;

                wb_cfg_4 <= wb_cfg_3;

                dest_addr_4 <= dest_addr_3;

                dest_cfg_4 <= dest_cfg_3;

                pcn_4 <= pcn_3;

                cond_jump_4 <= cond_jump_3;

                jz_4 <= jz_3;

                jal_4 <= jal_3;

              end

          end

  end

always @(wb_cfg_4 or ya_4 or cvnz_a_4 or yb_4 or cvnz_b_4 or spqa_4 or ext_cvnz_4 or ext_result_4)

  begin

    case (wb_cfg_4)

      4'b 0000 : wb_data = ya_4;

      4'b 0001 : wb_data = yb_4;

      4'b 0010 : wb_data = spqa_4;

      4'b 0011 : wb_data = ext_result_4;

      4'b 0100 : wb_data = { {31{1'b 0}} , cvnz_a_4[0]};  // Store Z

      4'b 0101 : wb_data = { {31{1'b 0}} , cvnz_a_4[1]};         // Store N

      4'b 0110 : wb_data = { {31{1'b 0}} , cvnz_a_4[2]};         // Store V

      4'b 0111 : wb_data = { {31{1'b 0}} , cvnz_a_4[3]};         // Store C

      4'b 1000 : wb_data = { {31{1'b 0}} , cvnz_b_4[0]};  // Store Z

      4'b 1001 : wb_data = { {31{1'b 0}} , cvnz_b_4[1]};         // Store N

      4'b 1010 : wb_data = { {31{1'b 0}} , cvnz_b_4[2]};         // Store V

      4'b 1011 : wb_data = { {31{1'b 0}} , cvnz_b_4[3]};         // Store C

      4'b 0100 : wb_data = { {31{1'b 0}} , ext_cvnz_4[0]};        // Store Z

      4'b 0101 : wb_data = { {31{1'b 0}} , ext_cvnz_4[1]};       // Store N

      4'b 0110 : wb_data = { {31{1'b 0}} , ext_cvnz_4[2]};       // Store V

      4'b 0111 : wb_data = { {31{1'b 0}} , ext_cvnz_4[3]};       // Store C

    endcase

  end

// Destination handling only write enable is instruction is valid

always @(dest_cfg_4 or inst_vld_4 or cond_jump_4 or yb_4[0] or jz_4 or set_pc)

  begin