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Table of contents

The zx-state file format
Block types

ZXSTZ80REGS

Contains the Z80 registers and other internal state values. It does not contain any specific model registers.

#define ZXSTZF_EILAST	1
#define ZXSTZF_HALTED	2

typedef struct _tagZXSTZ80REGS
{
  ZXSTBLOCK blk;
  WORD AF, BC, DE, HL;
  WORD AF1, BC1, DE1, HL1;
  WORD IX, IY, SP, PC;
  BYTE I;
  BYTE R;
  BYTE IFF1, IFF2;
  BYTE IM;
  DWORD dwCyclesStart;
  BYTE chHoldIntReqCycles;
  BYTE chFlags;
  WORD wMemPtr;
} ZXSTZ80REGS, *LPZXSTZ80REGS;

Members

blk
The block header. The block id is ZXSTBID_Z80REGS ('Z', '8', '0', 'R').
AF
The contents of the AF register pair
BC
The contents of the BC register pair
DE
The contents of the DE register pair
HL
The contents of the HL register pair
AF1
The contents of the AF' register pair
BC1
The contents of the BC' register pair
DE1
The contents of the DE' register pair
HL1
The contents of the HL' register pair
IX
The contents of the IX register pair
IY
The contents of the IY register pair
SP
The contents of the stack pointer, SP
PC
The current value of the program counter, PC
I
The contents of the I register
R
The contents of the R register
IFF1
The value of Interrupt Flip Flop 1 (IFF1). This is guaranteed to be either 0 or 1.
IFF2
The value of Interrupt Flip Flop 2 (IFF2). This is guaranteed to be either 0 or 1.
IM
The current Z80 interrupt mode. This can be 0, 1 or 2.
dwCyclesStart
The t-states value at the time the snapshot was made. This counts up from zero to the maximum number of t-states per frame for the specific Spectrum model.
chHoldIntReqCycles
The number of t-states left on restart when an interrupt can occur. This is used to support interrupt re-triggering properly.

On the Spectrum, the ULA holds the INTREQ line of the Z80 low for up to 48 t-states (depending on the model). If interrupts are enabled during this time, the Z80 will accept the request and invoke the appropriate interrupt service routine.

The AMX mouse also asserts the INTREQ line when it needs attention. It is therefore possible for this member to be non-zero even if the t-state counter suggests we are not at the beginning of a frame.

chFlags
Various flags indicating the internal state of the CPU. This can be a combination of:
FlagMeaning
ZXSTZF_EILASTThe last instruction executed was an EI instruction or an invalid $DD or $FD prefix.
ZXSTZF_HALTEDThe last instruction executed was a HALT instruction. The CPU is currently executing NOPs and will continue to do so until the next interrupt occurs.

This flag is mutually exclusive with ZXSTZF_EILAST.

wMemPtr
Internal Z80 register used to generate bits 5 and 3 of the F register after executing a BIT x,(HL) instruction. Set to 0 (zero) if not supported.

Revision history

Available since version 1.0.

The chFlags, chBitReg and chReserved members were added in version 1.1. The size of the block is unchanged.

The wMemPtr member was added in version 1.4. It replaces the chBitReg and chReserved members. The size of the block is unchanged.


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