| | 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 |
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