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z80: decide to remove embedded changelog from comments (refer to github history)
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// license:BSD-3-Clause
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// copyright-holders:Juergen Buchmueller
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/*****************************************************************************
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*
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* z80.cpp
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* Portable Z80 emulator V3.9
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*
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* TODO:
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* - Interrupt mode 0 should be able to execute arbitrary opcodes
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* - If LD A,I or LD A,R is interrupted, P/V flag gets reset, even if IFF2
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* was set before this instruction (implemented, but not enabled: we need
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* document Z80 types first, see below)
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* - Ideally, the tiny differences between Z80 types should be supported,
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* currently known differences:
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* - LD A,I/R P/V flag reset glitch is fixed on CMOS Z80
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* - OUT (C),0 outputs 0 on NMOS Z80, $FF on CMOS Z80
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* - SCF/CCF X/Y flags is ((flags | A) & 0x28) on SGS/SHARP/ZiLOG NMOS Z80,
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* (flags & A & 0x28).
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* However, recent findings say that SCF/CCF X/Y results depend on whether
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* or not the previous instruction touched the flag register.
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* This Z80 emulator assumes a ZiLOG NMOS model.
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*
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* Changes in 0.243:
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* Foundation for M cycles emulation. Currently we preserve cc_* tables with total timings.
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* execute_run() behavior (simplified) ...
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* Changes in 3.9:
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* - Fixed cycle counts for LD IYL/IXL/IYH/IXH,n [Marshmellow]
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* - Fixed X/Y flags in CCF/SCF/BIT, ZEXALL is happy now [hap]
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* - Simplified DAA, renamed MEMPTR (3.8) to WZ, added TODO [hap]
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* - Fixed IM2 interrupt cycles [eke]
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* Changes in 3.8 [Miodrag Milanovic]:
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* - Added MEMPTR register (according to informations provided
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* by Vladimir Kladov
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* - BIT n,(HL) now return valid values due to use of MEMPTR
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* - Fixed BIT 6,(XY+o) undocumented instructions
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* Changes in 3.7 [Aaron Giles]:
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* - Changed NMI handling. NMIs are now latched in set_irq_state
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* but are not taken there. Instead they are taken at the start of the
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* execute loop.
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* - Changed IRQ handling. IRQ state is set in set_irq_state but not taken
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* except during the inner execute loop.
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* - Removed x86 assembly hacks and obsolete timing loop catchers.
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* Changes in 3.6:
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* - Got rid of the code that would inexactly emulate a Z80, i.e. removed
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* all the #if Z80_EXACT #else branches.
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* - Removed leading underscores from local register name shortcuts as
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* this violates the C99 standard.
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* - Renamed the registers inside the Z80 context to lower case to avoid
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* ambiguities (shortcuts would have had the same names as the fields
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* of the structure).
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* Changes in 3.5:
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* - Implemented OTIR, INIR, etc. without look-up table for PF flag.
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* [Ramsoft, Sean Young]
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* Changes in 3.4:
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* - Removed Z80-MSX specific code as it's not needed any more.
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* - Implemented DAA without look-up table [Ramsoft, Sean Young]
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* Changes in 3.3:
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* - Fixed undocumented flags XF & YF in the non-asm versions of CP,
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* and all the 16 bit arithmetic instructions. [Sean Young]
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* Changes in 3.2:
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* - Fixed undocumented flags XF & YF of RRCA, and CF and HF of
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* INI/IND/OUTI/OUTD/INIR/INDR/OTIR/OTDR [Sean Young]
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* Changes in 3.1:
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* - removed the REPEAT_AT_ONCE execution of LDIR/CPIR etc. opcodes
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* for readabilities sake and because the implementation was buggy
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* (and i was not able to find the difference)
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* Changes in 3.0:
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* - 'finished' switch to dynamically overrideable cycle count tables
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* Changes in 2.9:
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* - added methods to access and override the cycle count tables
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* - fixed handling and timing of multiple DD/FD prefixed opcodes
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* Changes in 2.8:
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* - OUTI/OUTD/OTIR/OTDR also pre-decrement the B register now.
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* This was wrong because of a bug fix on the wrong side
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* (astrocade sound driver).
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* Changes in 2.7:
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* - removed z80_vm specific code, it's not needed (and never was).
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* Changes in 2.6:
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* - BUSY_LOOP_HACKS needed to call change_pc() earlier, before
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* checking the opcodes at the new address, because otherwise they
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* might access the old (wrong or even nullptr) banked memory region.
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* Thanks to Sean Young for finding this nasty bug.
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* Changes in 2.5:
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* - Burning cycles always adjusts the ICount by a multiple of 4.
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* - In REPEAT_AT_ONCE cases the r register wasn't incremented twice
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* per repetition as it should have been. Those repeated opcodes
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* could also underflow the ICount.
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* - Simplified TIME_LOOP_HACKS for BC and added two more for DE + HL
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* timing loops. i think those hacks weren't endian safe before too.
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* Changes in 2.4:
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* - z80_reset zaps the entire context, sets IX and IY to 0xffff(!) and
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* sets the Z flag. With these changes the Tehkan World Cup driver
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* _seems_ to work again.
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* Changes in 2.3:
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* - External termination of the execution loop calls z80_burn() and
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* z80_vm_burn() to burn an amount of cycles (r adjustment)
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* - Shortcuts which burn CPU cycles (BUSY_LOOP_HACKS and TIME_LOOP_HACKS)
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* now also adjust the r register depending on the skipped opcodes.
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* Changes in 2.2:
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* - Fixed bugs in CPL, SCF and CCF instructions flag handling.
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* - Changed variable ea and arg16() function to u32; this
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* produces slightly more efficient code.
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* - The DD/FD XY CB opcodes where XY is 40-7F and Y is not 6/E
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* are changed to calls to the X6/XE opcodes to reduce object size.
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* They're hardly ever used so this should not yield a speed penalty.
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* New in 2.0:
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* - Optional more exact Z80 emulation (#define Z80_EXACT 1) according
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* to a detailed description by Sean Young which can be found at:
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* http://www.msxnet.org/tech/z80-documented.pdf
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*****************************************************************************/
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ZiLOG Z80 emulator
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TODO:
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- Interrupt mode 0 should be able to execute arbitrary opcodes
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- If LD A,I or LD A,R is interrupted, P/V flag gets reset, even if IFF2
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was set before this instruction (implemented, but not enabled: we need
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document Z80 types first, see below)
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- Ideally, the tiny differences between Z80 types should be supported,
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currently known differences:
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- LD A,I/R P/V flag reset glitch is fixed on CMOS Z80
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- OUT (C),0 outputs 0 on NMOS Z80, $FF on CMOS Z80
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- SCF/CCF X/Y flags is ((flags | A) & 0x28) on SGS/SHARP/ZiLOG NMOS Z80,
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(flags & A & 0x28).
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However, recent findings say that SCF/CCF X/Y results depend on whether
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or not the previous instruction touched the flag register.
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This Z80 emulator assumes a ZiLOG NMOS model.
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*****************************************************************************/
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#include "emu.h"
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#include "z80.h"
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@ -615,7 +527,7 @@ void z80_device::device_start()
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// sbc with carry set
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val = oldval - newval - 1;
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*psbc = NF | ((newval) ? ((newval & 0x80) ? SF : 0) : ZF);
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*psbc |= (newval & (YF | XF)); /* undocumented flag bits 5+3 */
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*psbc |= (newval & (YF | XF)); // undocumented flag bits 5+3
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if( (newval & 0x0f) >= (oldval & 0x0f) ) *psbc |= HF;
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if( newval >= oldval ) *psbc |= CF;
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if( (val^oldval) & (oldval^newval) & 0x80 ) *psbc |= VF;
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