Timings.md

Introduction

47loader supports several different timings that you can select at assemble time. You can thus customize the loader for the speed and loading sound that you want.

Available timings

Name	Pilot pulse length	Zero pulse length	One pulse length	Percentage of ROM loader speed	Remarks
FAST	1710T	475T	950T	~185%
EAGER	1710T	509T	1018T	~170%
STANDARD	1710T	543T	1086T	~160%	The default speed if none is selected.
CAUTIOUS	1710T	611T	1222T	~145%
CONSERVATIVE	1710T	679T	1358T	~130%
SPEEDLOCK7	1710T	713T	1426T	~125%	Almost identical to the speed of the slower Speedlock loaders.
ROM	2168T	855T	1710T	100%	The same timings as used by the ROM loader.

How to choose a timing

You must specify the timing in two places:

1. by defining a symbol in your code;
2. as an option to 47loader-tzx when you create the TZX file.

Assemble-time symbols

Define a symbol LOADER_SPEED_*, where * is one of the names in the above table. Here is a simple example using the fastest-supported timings:

        ;; this is the border theme to use.  A full list of the
        ;; available themes is on the Wiki:
        ;; https://code.google.com/p/47loader/wiki/BorderThemes
LOADER_THEME_RAINBOW:equ 1
        ;; this is the symbol specifying the timing
LOADER_SPEED_FAST:equ 1

        ;; place the loader into uncontended memory
        org     32768

        ;; load a screen directly into the video RAM
        ld      ix,16384
        ld      de,6912
        call    loader

        ;; load 8144 bytes at address 49152
        ld      ix,49152
        ld      de,8144
        call    loader

        ;; jump to the code we just loaded
        jp      49152

loader:
        ;; call the loader proper
        call    loader_entry
        ;; carry set means success
        ret     c
        ;; if failed, drop into error handler
        include "47loader_error_handler.asm"

        include "47loader.asm"

47loader-tzx's -speed option

The -speed option takes one of the timing names as a parameter. The timing name is case-insensitive. To create a tape file suitable for use with the above example, do:

47loader-tzx -speed fast -output mygame.tzx mygame.scr
47loader-tzx -speed fast -output mygame.tzx mygame.bin

Notes about ROM timings

If you use the ROM timings, you will notice that the assembled 47loader code increases in size somewhat. This is because ROM timings are supported in addition to turbo timings: extra code is generated to detect which timings to use from the frequency of the pilot tone. The assemble-time option LOADER_SUPPORT_ROM_TIMINGS may be set in addition to any of the turbo timing options to produce a loader that supports both ROM timings and the turbo speed of your choice. Here is a simple example specifying a loader that supports both ROM and FAST speeds:

        ;; this is the border theme to use.  A full list of the
        ;; available themes is on the Wiki:
        ;; https://code.google.com/p/47loader/wiki/BorderThemes
LOADER_THEME_RAINBOW:equ 1
        ;; this is the symbol specifying the timings
LOADER_SPEED_FAST:equ 1
        ;; additionally, support ROM timings
LOADER_SUPPORT_ROM_TIMINGS:equ 1

        ;; place the loader into uncontended memory
        org     32768

        ;; load a screen directly into the video RAM
        ld      ix,16384
        ld      de,6912
        call    loader

        ;; load 8144 bytes at address 49152
        ld      ix,49152
        ld      de,8144
        call    loader

        ;; jump to the code we just loaded
        jp      49152

loader:
        ;; call the loader proper
        call    loader_entry
        ;; carry set means success
        ret     c
        ;; if failed, drop into error handler
        include "47loader_error_handler.asm"

        include "47loader.asm"

With a loader created like that, you can do:

47loader-tzx -speed fast -output mygame-turbo.tzx mygame.scr
47loader-tzx -speed fast -output mygame-turbo.tzx mygame.bin
47loader-tzx -speed rom -output mygame-slow.tzx mygame.scr
47loader-tzx -speed rom -output mygame-slow.tzx mygame.bin

Now you have two TZX files created from the same source. You could distribute both of them together; anyone wanting to make a tape to load into a real Spectrum but who has trouble with recording reliable turbo tapes can use the slow TZX instead.