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redcode
2022-08-01 19:35:47 +02:00
parent bab1800393
commit 25ff1d8bd6
1 changed files with 15 additions and 23 deletions
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sources/Z80.c
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@@ -32,31 +32,23 @@
| A12 <-02--| |--39-> A09 that can stand the test of time |
| A13 <-03--| |--38-> A08 with no need for major changes. |
| A14 <-04--| |--37-> A07 |
| A15 <-05--| |--36-> A06 Everything that is known about the |
| CLK --06->| |--35-> A05 Z80 is emulated here, including |
| D4 <-07->| |--34-> A04 the interrupt mode 0, which has |
| D3 <-08->|.---------.|--33-> A03 not been fully implemented to date |
| D5 <-09->|| ZILOG ||--32-> A02 in any other known open source Z80 |
| D6 <-10->|| Z80 ||--31-> A01 emulator. This is, therefore, the |
| +5V --11--|| CPU ||--30-> A00 first complete and free emulator. |
| A15 <-05--| |--36-> A06 Some of the main design decisions |
| CLK --06->| |--35-> A05 have been the following: |
| D4 <-07->| |--34-> A04 |
| D3 <-08->|.---------.|--33-> A03 1. Opcode partial decoding keeps |
| +5V --11--|| CPU ||--30-> A00 the code small and maintainable. |
| D2 <-12->|| ||--29-- GND |
| D7 <-13->|'---------'|--28-> RFSH Some of the main design decisions |
| D0 <-14->| |--27-> M1 have been the following: |
| D1 <-15->| |<-26-- RESET |
| INT --16->| |<-25-- BUSREQ 1. The logic of the opcodes has |
| NMI --17->| |<-24-- WAIT been separated from that of the |
| HALT <-18--| |--23-> BUSACK arguments to reduce the size of |
| MREQ <-19--| |--22-> WR the emulator, thus increasing the |
| IORQ <-20--| |--21-> RD possibility that the CPU loads all |
| '-----------' its code in the L1 cache. |
| D7 <-13->|'---------'|--28-> RFSH 2. Function pointer tables for |
| D0 <-14->| |--27-> M1 opcode selection allow easy reuse |
| D1 <-15->| |<-26-- RESET of almost all instruction code |
| INT --16->| |<-25-- BUSREQ in the interrupt mode 0. |
| NMI --17->| |<-24-- WAIT |
| HALT <-18--| |--23-> BUSACK 3. Avoiding conditional statements |
| MREQ <-19--| |--22-> WR as much as possible reduces the |
| IORQ <-20--| |--21-> RD branch penalty in modern pipelined |
| '-----------' processors. |
| Zilog Z80 CPU, May 1976 version |
| 40-pin ceramic DIP pinout 2. The use of function pointer |
| tables has been chosen over large |
| switch statements for opcode selection. This allows easy reuse of almost |
| all instruction emulation code in the interrupt mode 0. |
| |
| 3. Special attention has been given to avoid conditional statements as |
| much as possible to reduce the branch penalty in pipelined processors. |
| 40-pin ceramic DIP pinout Manuel |
| |
'=============================================================================*/