git.joshuawise.com / fpgaboy.git / blame
| Commit | Line | Data |
|---|---|---|
| e7fe9dc2 JW |
1 | `define INSN_RET 9'b0110x1001 // 1 = RETI, 0 = RET |
| 2 | `define INSN_RETCC 9'b0110xx000 | |
| 3 | ||
| df770340 JW |
4 | `ifdef EXECUTE |
| 5 | `INSN_RET,`INSN_RETCC: begin | |
| 6 | case (cycle) | |
| 5c33c5c0 | 7 | 0: `EXEC_READ(`_SP) |
| df770340 | 8 | 1: begin // SPECIAL CASE: cycle does NOT increase linearly with ret! |
| 5c33c5c0 | 9 | `EXEC_INC_PC // cycle 1 is skipped if we are not retcc |
| df770340 | 10 | case (opcode[4:3]) |
| b4f3ac35 JW |
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 | |
| df770340 | 15 | endcase |
| 5c33c5c0 | 16 | `EXEC_READ(`_SP) // retry the read |
| df770340 | 17 | end |
| 5c33c5c0 | 18 | 2: `EXEC_READ(`_SP + 1) |
| df770340 | 19 | 3: begin /* twiddle thumbs */ end |
| 5c33c5c0 | 20 | 4: `EXEC_NEWCYCLE |
| df770340 JW |
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 | |
| 5c33c5c0 JW |
31 | 2: `_PCL <= rdata; |
| 32 | 3: `_PCH <= rdata; | |
| df770340 | 33 | 4: begin |
| 5c33c5c0 | 34 | `_SP <= `_SP + 2; |
| df770340 JW |
35 | if (opcode[4] && opcode[0]) /* RETI */ |
| 36 | ie <= 1; | |
| 37 | end | |
| 38 | endcase | |
| 39 | end | |
| 40 | `endif |