Speed and time¶

The machine normally runs at the speed of the real one, about 50 frames a second. The Machine menu has the commands that change that: Pause, Fast Mode, Slow Motion and Fast Forward. The same commands, and Rewind too, are at the right end of the toolbar. Their settings are on the Emulation page of Options.

Pause¶

Machine > Pause stops the machine, and the same command again lets it continue. The status bar says paused, and a pause sign shows in the top right corner of the picture. The key is Pause in both presets.

The machine also waits while Options, a file dialog or the Debugger is open, and continues when that window closes.

The Pause group on the Emulation page of Options has three more ways:

Pause when inactive - the machine stops whenever you switch to another program, and continues when you come back to the window. Off by default.
Pause in menus - the machine waits while a menu of the window is open: the menu bar, the right-click menu, the menus over the picture in fullscreen, a list from the toolbar. It continues when the menu closes; a command that opens a window keeps it stopped until that window closes. The volume slider does not stop it - you set the volume by ear. Save History holds it too, opened from the menu or by its key, as the place to pick a save from. On by default.
Resume by input - after Machine > Pause, the first key you press, a click in the picture, a click on the Virtual Keyboard or a pad button lets the machine go on. The key and the pad button reach the game, so the character moves at once; the click only ends the pause, it is not a fire for a mouse. Hotkeys work while paused and do not end it, nor do Shift, Ctrl, Alt or the lock keys alone. It ends only your own pause: not the one of Options, a dialog, the Debugger, an RZX recording’s player or Pause when inactive. Off by default.

A menu never takes your own pause off: if you paused the machine, it stays paused after the menu closes.

Fast Mode¶

Machine > Fast Mode runs the machine as fast as the computer can, with no sound. Use it to get through a long wait - a slow loader, a long calculation. The title bar says fast while it is on, and anti-flicker is not applied.

The number in the Fast Mode render row of the Emulation page is how many frames a second Fast Mode shows, from 1 to 100 (30 by default); the frames between are not drawn. Fast loading of a tape shows the same number of frames a second.

Any pause ends Fast Mode; Machine > Pause first lets the machine finish the frame, so the picture is whole. Fast Mode cannot be started while the machine is paused.

Slow Motion and Fast Forward¶

Machine > Slow Motion runs the whole machine slower, picture and sound alike: 1/2, 1/4 (the default) or 1/8 of the normal speed. Machine > Fast Forward runs it faster, x2, x4 (the default), x8 or x16, and the sound plays sped up. The speeds are set in the Slow Motion and Fast Forward rows of the Emulation page of Options.

The Faster and Slower hotkeys, Shift+Num++ and Shift+Num+- in both presets, step through all of these: 1/8, 1/4, 1/2, normal speed, x2, x4, x8, x16. Hold one down and it keeps stepping. The speeds set for Slow Motion and Fast Forward stay as they are: their keys and buttons always run at those.

How fast x8 and x16 really run depends on the computer: when it cannot keep up, the machine runs as fast as it can. The ZX Evolution in TSConf mode and the ZX Spectrum Next need the most from it.

Both always start from normal speed: switching one on switches the other off, and moving the Overclock slider ends either of them. Opening a file or switching to another machine brings the speed back to normal too.

A sign in the top right corner of the picture shows which mode is on.

How the keys work¶

The Slow Motion, Fast Forward and Fast Mode, no limit rows of the Emulation page each end in a list that says how the key of that mode works:

Toggle - a press switches the mode on, the next press switches it off;
Hold - the mode is on only while the key is held down;
Tap or hold (the default) - a short tap switches it on or off, a longer press keeps it on only while the key is held.

The Slow Motion, Fast Forward and Fast Mode buttons on the toolbar work as their keys do: a press is the key’s press, letting go is the key’s release. In the Machine menu a click switches the mode on or off, whatever the key setting. The Slow Motion and Fast Forward icons show the speed set for them.

Rewind¶

Rewind takes you back in time: hold the Rewind (Hold) key - Del in both presets - or hold the Rewind button on the toolbar down. The picture runs backwards, with the sound played backwards too, and the sign in the top right corner shows how many seconds back you are. Let go, and the machine continues from the picture on the screen. Everything that came after that picture is gone.

Rewind is on by default. Machine > Allow Rewind switches it off and on; with it off, the Rewind button is grayed out. While it is on, the program keeps a history of the machine in memory, a snapshot every few frames. This takes 20 to 45 MB with the default settings and costs a little emulation speed. How the history is kept is in Keeping time and going back.

Rewind on the Emulation page of Options is the same switch, with two settings beside it:

Step - frames between two snapshots, from 1 to 50 (3 by default). When you rewind, each frame shown is one snapshot earlier, so a smaller step rewinds more slowly and smoothly, and keeps more snapshots in memory.
History - how far back you can go, from 5 to 300 seconds (30 by default).

The history starts over when:

the machine writes to a floppy disk, a hard disk or an SD card - the disk could not be put back as it was;
you switch to another machine, or change a machine setting in Options that the history depends on;
you change Step or History;
an RZX recording starts or ends, or an RZX file starts or stops playing.

While a tape is being recorded, no history is kept and rewind does not start. Fast loading of a tape is not kept either: when you rewind, the picture jumps over it.

Overclock and Turbo Mode¶

Two more controls change how fast the CPU runs, and both are described in Turbo Mode and Overclock:

Machine > Turbo Mode is the board’s own turbo, a part of the machine like on the real one. A program can switch it by itself.
The Overclock slider on the Machine page of Options belongs to the emulator. It makes only the CPU faster: the frame rate, the music and everything timed by the frame stay at normal speed, while a program that is slow because of the CPU - a 3D game, say - runs faster. The Overclock Up and Overclock Down hotkeys move the slider.

Fast Forward is different from both: it speeds up the whole machine, frames and sound included, as if time ran faster.

While the CPU runs at a clock other than its base clock, the CPU clock indicator can show that clock over the picture (see Indicators on the picture). The status bar shows the clock all the time.