# rzxplay.py

## SYNOPSIS

`rzxplay.py` [options] FILE [OUTFILE]

## DESCRIPTION

`rzxplay.py` plays an RZX file. If ‘OUTFILE’ is given, an SZX or Z80 snapshot or an RZX file is written after playback has completed.

## OPTIONS

`-c, --cmio`

  Simulate memory and I/O contention delays and the MEMPTR register.

`--flags FLAGS`

  Set playback flags. Do `--flags help` for more information, or see the section on `FLAGS` below.

`--force`

  Force playback when an unsupported machine is detected.

`--fps FPS`

  Run at this many frames per second (default: 50). 0 means maximum speed.

`--map FILE`

  Log addresses of executed instructions to a file.

`--no-screen`

  Run without a screen.

`--python`

  Use the pure Python Z80 simulator even if the C version is available.

`--quiet`

  Don’t print progress percentage during playback.

`--scale SCALE`

  Scale the display up by this factor (1-4; default: 2).

`--snapshot FILE`

  Specify an external snapshot file to start with.

`--stop FRAMES`

  Stop after playing this many frames.

`--trace FILE`

  Log executed instructions to a file.

`-V, --version`

  Show the SkoolKit version number and exit.

## SUPPORTED MACHINES

`rzxplay.py` can play RZX files that were recorded in 48K, 128K or +2 mode with no peripherals (e.g. Interface 1) attached. If any peripherals are attached, playback may fail. The `--force` option can be used to make `rzxplay.py` attempt playback of a file that was recorded on an unsupported machine, but it is unlikely to play to the end.

## SCREEN

If pygame is installed, `rzxplay.py` will use it to render the Spectrum’s screen contents at 50 frames per second by default. Use the `--fps` option to change the frame rate. Specifying `--fps 0` makes `rzxplay.py` run at maximum speed. To disable the screen and make `rzxplay.py` run even faster, use the `--no-screen` option.

## CODE EXECUTION MAP

The `--map` option can be used to log the addresses of instructions executed during playback to a file. This file can then be used by `sna2ctl.py` to produce a control file. If the file specified by the `--map` option already exists, any addresses it contains will be merged with those of the instructions executed.

## FLAGS

The `--flags` option sets flags that control the playback of RZX frames when interrupts are enabled. If an RZX file fails to play to completion, setting one or more of these flags may help. `FLAGS` is the sum of the following values, chosen according to the desired outcome:

- 1 - When the last instruction in a frame is either ‘LD A,I’ or ‘LD A,R’, reset bit 2 of the flags register. This is the expected behaviour of a real Z80, but some RZX files fail when this flag is set.

- 2 - When the last instruction in a frame is ‘EI’, and the next frame is a short one (i.e. has a fetch count of 1 or 2), block the interrupt in the next frame. By default, and according to RZX convention, `rzxplay.py` accepts an interrupt at the start of every frame except the first, regardless of whether the instruction just executed would normally block it. However, some RZX files contain a short frame immediately after an ‘EI’ to indicate that the interrupt should in fact be blocked, and therefore require this flag to be set to play back correctly.

- 4 - Ignore any snapshots after the first one. By default, `rzxplay.py` will use a snapshot embedded in an RZX file to update its internal state (i.e. memory and registers) before continuing to process the next input recording block. However, some RZX files created by the Fuse emulator do not play correctly under that scheme, and require this flag to be set.

## OUTPUT FILE

If `OUTFILE` is given, and ends with either ‘.z80’ or ‘.szx’, then a snapshot in the corresponding format is written when playback ends. Similarly, if `OUTFILE` ends with ‘.rzx’, then an RZX file is written when playback ends. However, this makes sense only if `--stop` is used to end playback somewhere in the middle of the input RZX file, otherwise the output RZX file will be empty (i.e. contain no frames).

## EXAMPLES

1. Play `game.rzx`:

`rzxplay.py game.rzx`

2. Log the instructions executed while playing `game.rzx`:

`rzxplay.py --trace game.log game.rzx`

3. Play only 100 frames of `game.rzx` and then write `game-100.rzx`:

`rzxplay.py --stop 100 game.rzx game-100.rzx`