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zx81get.1
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.\" -*- nroff -*-
.\"
.\" zx81get.1
.\"
.TH zx81get 1 "23rd April, 1999" "Version 1.0" "Emulators"
.\"
.\"------------------------------------------------------------------
.\"
.SH NAME
zx81get \- load ZX81 programs from tape via /dev/dsp
.\"
.\"------------------------------------------------------------------
.\"
.SH SYNOPSIS
.PD 0
.B zx81get
.RB [ -v ]
.P
.PD 1
.\"
.\"------------------------------------------------------------------
.\"
.SH DESCRIPTION
Zx81get reads ZX81 programs (generally from tape) via /dev/dsp, i.e.,
using a soundcard. It writes (or verifies) the files under the
filenames they were saved with, in the `.P' format supported by z81.
.PP
Usage is either simply `zx81get', to transfer files, or `zx81get -v',
to verify files which have already been transferred. Once you're
finished, you can raise SIGINT (e.g. by doing a ^C) to exit zx81get.
.\"
.\"------------------------------------------------------------------
.\"
.SH OPTIONS
.TP
.I -v
verify existing files (instead of writing new ones). After running
zx81get to copy files from a tape, you should generally verify that
the files were read correctly by going through the tape a second time
with `zx81get -v'.
.\"
.\"------------------------------------------------------------------
.\"
.SH "TROUBLESHOOTING"
The main problem you're likely to have getting zx81get to work is
getting the output from the tape player at the right level (just the
same as when loading on a real ZX81, in fact :-)). Generally you want
it to fill the sample range as much as possible, but this isn't easy
to judge. Some ideas which may help:
.PP
- if you can't hear the tape hiss shortly before the program data
starts, it's probably not loud enough.
.PP
- if
.I all
you can hear is tape hiss, it's probably too loud. :-)
.PP
- as a general guide, the sound should be uncomfortably loud, but not
ear-splitting.
.PP
- an alternative approach to the above is to push the volume as far as
it will go without distorting.
.PP
But apart from that, you'll just have to experiment to find the most
reliable settings.
.PP
Two other problems are caused by inadequacies in the ZX81's tape
format:
.PP
Firstly, there is no lead-in tone, so if your sampling device uses an
auto-gain control (a manifestation of purest evil) on its `mic' input,
you may want to try `line-in' or similar instead, as an AGC will
completely destroy the start of the signal.
.PP
(If you're not familiar with the effect of an AGC, listen to the way
the volume changes on the input. If it gets louder and louder (to a
certain point) during silent parts, then suddenly adjusts when the
program starts, it's likely an AGC is involved.)
.PP
Secondly, there is no checksum, no CRC, absolutely no check of any
kind whatsoever. That means there's no way to tell if what you've
loaded bears even the slightest resemblance to what was saved. As
such, I
.I strongly
recommend you use the
.RI ` -v '
option after reading a tape to `verify' the files.
.PP
Another recommendation - if you have any Psion programs (e.g.
.IR "Flight Simulation" ),
try them first, as they do a CRC check when they start up. If you can
get such a check to work, you can be reasonably confident that you
have a working setup.
.\"
.\"------------------------------------------------------------------
.\"
.SH BUGS
The sound device must be capable of 22kHz 8-bit mono recording.
.PP
The boundary between noise (bits) and silence (gaps between them) is
hard-coded; it might be better if that could be adjusted.
.PP
I don't have that many ZX81 tapes any more, so I could only test it on
15 programs, the largest of which wasn't much over 4k. (I'd appreciate
knowing if it seems to be at all reliable for larger programs - it
should be, but I can't easily check.)
.\"
.\"------------------------------------------------------------------
.\"
.SH SEE ALSO
.IR z81 "(1)"
.\"
.\"------------------------------------------------------------------
.\"
.SH AUTHOR
Russell Marks ([email protected]).