988260c699
This PR is the second of two PRs that replaces earlier PRs #2589 and #2590. Due to a git branching mishap it was decided to re-partition the new functionality in two sequential PRs that offer self-contained, new functionality to sim65. The functionality in this second and last PR provides the following things in relation to the new "peripheral" support: * C support: there is now an include/sim65.h that can be included from C. It provides access to the memory-mapped peripheral addresses. * Asm support: there is now an asminc/sim65.inc that can be included from assembly. It provides symbolic labels for the memory-mapped peripheral addresses. Note: the two items above are implemented by adding a "_peripherals" symbol to cfg/sim6502.cfg and cfg/sim65c02.cfg, with the fixed base address of the peripherals memory aperture (0xffc0). * Updated the sim65 documentation to describe the peripherals in some detail, with examples that show to use the new features from within C. * Some examples in the new samples/sim5/ directory. These are currently not integrated in the build system (in other words, there's no Makefile there), because I don't know how to do that. I will happily implement that after #2582 is taken care of. If that is not acceptable, the next best thing will be for somebody else (who understands how the Makefiles are set up) to take care of this. If that's not going to happen, and we don't want examples that are not properly integrated with the build system, there's always the option of removing these samples from the PR.
105 lines
3.7 KiB
C
105 lines
3.7 KiB
C
/*
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* Sim65 cpu-mode switching example.
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*
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* Description
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* -----------
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*
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* We can inspect and manipulate the CPU model that sim65 emulates at runtime.
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*
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* Sim65 always runs in one of three modes:
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*
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* - 6502 mode: the 151 documented opcodes are supported; if the processor encounters
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* one of the 105 undocumented opcodes, the simulator ends with an
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* 'illegal opcode' message.
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* - 65C02 mode: the 105 undocumented opcodes now have well-defined behavior. Some
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* do useful things, while all others are now defined as NOPs.
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* - 6502X mode: the 105 undocumented opcodes don't have documented behavior, but
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* they /do/ have behavior on a real 6502. This behavior has been
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* figured out, and is deterministic (with minor exceptions).
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* In this mode, sim65 mimics the behavior of a real 6502 when
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* it encounters an undocumented opcode, rather than terminating.
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*
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* In the example below, we first switch to 6502X mode and execute a small
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* assembly code fragment, then repeat this in 65C02 mode.
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*
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* The code fragment is designed to distinguish between a 6502 and a 65C02
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* processor based on the behavior of the ADC function in decimal mode.
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*
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* Important Note:
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*
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* When running in a program compiled for the "sim6502" target, it is safe to switch to
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* 65C02 or 6502X mode, since the runtime library will only use plain 6502 opcodes, and
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* those work the same in 65C02 and 6502X mode.
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*
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* However, when running in a program compiled for the "sim65c02" target, it is NOT safe
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* to switch to 6502 or 6502X mode, since many routines in the runtime library use
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* 65C02-specific opcodes, and these will not work as expected when the CPU is switched
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* to 6502 or 6502X mode. When such an instruction is encountered, the program will
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* exhibit undefined behavior.
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*
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* For this reason, this program will only work when compiled for the "sim6502" target.
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*
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* Running the example
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* -------------------
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*
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* cl65 -t sim6502 -O cpumode_example.c -o cpumode_example.prg
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* sim65 cpumode_example.prg
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*
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*/
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#include <stdio.h>
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#include <stdbool.h>
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#include <sim65.h>
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static bool __fastcall__ is_65c02(void)
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{
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/* This assembly routine loads 0 into AX on a 6502 (also on a 6502 on which decimal
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* mode is not implemented), and 1 on a 65C02.
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*
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* Note: this implementation triggers a "control reaches end of non-void function"
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* warning that can be safely ignored. While no return statement is present, the
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* return value is correctly loaded into AX by the assembly code.
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*/
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__asm__("ldx #0");
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__asm__("sed");
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__asm__("txa");
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__asm__("sbc #28");
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__asm__("asl a");
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__asm__("sbc #28");
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__asm__("and #1");
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__asm__("cld");
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}
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int main(void)
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{
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printf("CPU mode at startup ....... : %u\n", GET_CPU_MODE());
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printf("Is 65C02? ................. : %s\n", is_65c02() ? "YES" : "NO");
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printf("\n");
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printf("Switching to 6502 mode ....\n");
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SET_CPU_MODE(SIM65_CPU_MODE_6502);
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printf("Current CPU mode .......... : %u\n", GET_CPU_MODE());
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printf("Is 65C02? ................. : %s\n", is_65c02() ? "YES" : "NO");
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printf("\n");
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printf("Switching to 65C02 mode ...\n");
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SET_CPU_MODE(SIM65_CPU_MODE_65C02);
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printf("Current CPU mode .......... : %u\n", GET_CPU_MODE());
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printf("Is 65C02? ................. : %s\n", is_65c02() ? "YES" : "NO");
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printf("\n");
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printf("Switching to 6502X mode ...\n");
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SET_CPU_MODE(SIM65_CPU_MODE_6502X);
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printf("Current CPU mode .......... : %u\n", GET_CPU_MODE());
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printf("Is 65C02? ................. : %s\n", is_65c02() ? "YES" : "NO");
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printf("\n");
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printf("Bye!\n");
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return 0;
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}
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