insn_ret-retcc.v

   1 `ifdef EXECUTE
   2         `INSN_RET,`INSN_RETCC: begin
   3                 case (cycle)
   4                 0:      `EXEC_READ(`_SP)
   5                 1:      begin   // SPECIAL CASE: cycle does NOT increase linearly with ret!
   6                                 `EXEC_INC_PC    // cycle 1 is skipped if we are not retcc
   7                                 case (opcode[4:3])
   8                                 `INSN_cc_NZ:    if (registers[`REG_F][7]) `EXEC_NEWCYCLE
   9                                 `INSN_cc_Z:     if (~registers[`REG_F][7]) `EXEC_NEWCYCLE
  10                                 `INSN_cc_NC:    if (registers[`REG_F][4]) `EXEC_NEWCYCLE
  11                                 `INSN_cc_C:     if (~registers[`REG_F][4]) `EXEC_NEWCYCLE
  12                                 endcase
  13                                 `EXEC_READ(`_SP)        // retry the read
  14                         end
  15                 2:      `EXEC_READ(`_SP + 1)
  16                 3:      begin /* twiddle thumbs */ end
  17                 4:      `EXEC_NEWCYCLE
  18                 endcase
  19         end
  20 `endif
  21
  22 `ifdef WRITEBACK
  23         `INSN_RET,`INSN_RETCC: begin
  24                 case (cycle)
  25                 0:      if (opcode[0])  // i.e., not RETCC
  26                                 cycle <= 1;     // Skip cycle 1; it gets incremented on the next round.
  27                 1:      begin /* Nothing need happen here. */ end
  28                 2:      `_PCL <= rdata;
  29                 3:      `_PCH <= rdata;
  30                 4:      begin
  31                                 `_SP <= `_SP + 2;
  32                                 if (opcode[4] && opcode[0])     /* RETI */
  33                                         ie <= 1;
  34                         end
  35                 endcase
  36         end
  37 `endif