core/insn_ret-retcc.v

   1 `define INSN_RET                9'b0110x1001    // 1 = RETI, 0 = RET
   2 `define INSN_RETCC              9'b0110xx000
   3
   4 `ifdef EXECUTE
   5         `INSN_RET,`INSN_RETCC: begin
   6                 case (cycle)
   7                 0:      `EXEC_READ(`_SP)
   8                 1:      begin   // SPECIAL CASE: cycle does NOT increase linearly with ret!
   9                                 `EXEC_INC_PC    // cycle 1 is skipped if we are not retcc
  10                                 case (opcode[4:3])
  11                                 `INSN_cc_NZ:    if (`_F[7])  `EXEC_NEWCYCLE
  12                                 `INSN_cc_Z:     if (~`_F[7]) `EXEC_NEWCYCLE
  13                                 `INSN_cc_NC:    if (`_F[4])  `EXEC_NEWCYCLE
  14                                 `INSN_cc_C:     if (~`_F[4]) `EXEC_NEWCYCLE
  15                                 endcase
  16                                 `EXEC_READ(`_SP)        // retry the read
  17                         end
  18                 2:      `EXEC_READ(`_SP + 1)
  19                 3:      begin /* twiddle thumbs */ end
  20                 4:      `EXEC_NEWCYCLE
  21                 endcase
  22         end
  23 `endif
  24
  25 `ifdef WRITEBACK
  26         `INSN_RET,`INSN_RETCC: begin
  27                 case (cycle)
  28                 0:      if (opcode[0])  // i.e., not RETCC
  29                                 cycle <= 1;     // Skip cycle 1; it gets incremented on the next round.
  30                 1:      begin /* Nothing need happen here. */ end
  31                 2:      `_PCL <= rdata;
  32                 3:      `_PCH <= rdata;
  33                 4:      begin
  34                                 `_SP <= `_SP + 2;
  35                                 if (opcode[4] && opcode[0])     /* RETI */
  36                                         ie <= 1;
  37                         end
  38                 endcase
  39         end
  40 `endif