Using Z88 Snapshots

A Z88 snapshot (a .z88 file) is a complete freeze of a Cambridge Z88: the Z80 registers, the Blink chip’s registers, the internal ROM and RAM, and the cards in the three slots. The format comes from the OZvm  emulator and is documented in its wiki .

Klive can show you what a snapshot contains, and load it into the Cambridge Z88 machine to run it or debug it from the exact instruction where it was saved. That makes a snapshot a ready-made debug setup: save the machine in OZvm just before the code you are interested in, then continue from there in Klive.

Viewing a snapshot

Open a .z88 file from the Explorer to see its contents:

• Snapshot: whether Klive can load it (and if not, why), its Autorun flag, when it was saved, the real-time clock as saved and as it will be after loading, the files inside the snapshot, and the picture of the LCD that OZvm saved with it.
• Z80 Registers and Blink: the saved state, with the set bits of COM, INT, STA, TMK and TSTA named.
• Address Space at PC: which bank and offset the program counter is in, and which bank is paged into each address range. The two buttons in the heading open the 64K the CPU sees as a memory dump or a disassembly, positioned at the program counter.
• Slots: every bank of every card in one list, grouped by card (the slot-0 ROM, the internal RAM, and every card in slots 1–3). Each card’s heading shows its type, its size, and what it loads as in Klive. A bank’s row is marked with the segment registers that page it in (SR0–SR3, or $0000 for the fixed lower 8K), with PC or SP when the program counter or stack pointer points into it, and with empty when it holds only erased bytes ($FF on ROM, EPROM and Flash, $00 on RAM). The buttons above the list show all banks, only non-empty ones, only paged-in ones, or one card’s. Select a bank to see its details: where it is paged in, the other bank numbers that reach it (a card smaller than its slot repeats across the slot), and any breakpoints OZvm saved in it.
• Pop out a bank — with its row’s icon, by double-clicking the row, or with Enter — to open it as its own document, as a memory dump or a disassembly (the arrow beside Pop out chooses). The disassembly starts at the address the snapshot pages the bank in, or $C000 when it is not paged in, and reads the bytes as Z88 code: OZ system calls after RST 20h are decoded, whatever machine the emulator is running. Go Back returns to the viewer.
• Breakpoints: the breakpoints OZvm saved with the snapshot, for reference.

Loading, running and debugging

There are two ways to load a snapshot:

• Run (play icon): the machine runs from the snapshot’s state.
• Debug (debug icon): the machine starts in debug mode and stops at the snapshot’s program counter before executing that instruction, so the CPU, Memory and Disassembly panels show the saved state. Step from there, or continue with your breakpoints active.

You can reach them from:

• the buttons in a .z88 document’s tab;
• the Explorer’s context menu on a .z88 file;
• the z88-snapshot command;
• the Emulator’s Machine menu, while the machine is a Cambridge Z88: Open Z88 Snapshot… does what the file’s Autorun flag says, as OZvm does — it runs the snapshot if the flag is set, and stops in the debugger at the program counter if it is not.

Klive makes the machine fit the snapshot. If the current machine is not a Cambridge Z88, or its internal RAM or LCD size differs from the snapshot’s, the machine is set up again first. The cards of slots 1–3 are recorded in the machine configuration, so the card dialogs show them.

The real-time clock

The Z88’s real-time clock kept running in the real world while the snapshot sat on disk. When Klive loads a snapshot, it advances the clock by the time that passed since the snapshot was saved, as OZvm does, so the Z88’s time and alarms stay in step with your computer’s clock.

What Klive can load

The internal RAM can be 32K, 64K, 128K, 256K or 512K. Slot 0 accepts a ROM, a UV EPROM, or a 512K Flash chip. If a snapshot contains anything else, the viewer lists every reason, and loading reports them instead of loading part of the machine.

An LCD size Klive does not offer (it offers 640 × 64, 256, 320 and 480 pixels) does not stop the load: the machine keeps its current LCD size, with a warning.

Things to know

• The snapshot’s cards come from the file, not from card images on disk. Hard reset (and anything else that sets the machine up again) re-inserts the configured slot-0 ROM and blank cards in slots 1–3, so the snapshot is gone. Soft reset keeps the memory, as the reset button of a real Z88 does.
• OZvm’s saved breakpoints are shown in the viewer but not added to Klive’s breakpoints.
• Klive loads snapshots; it does not save them.