Iván Izaguirre
4fc0aa6652
DOS turns the drive off at the end of each access. At the start of the next it reads the data latch eight times, comparing each read with one 14 cycles later, to tell whether the disk still turns; if it does not seem to, it waits for the motor to come up to speed, close to a second. With the Disk II card and a DSK, PO or NIB diskette that wait was paid on every access, and a DOS 3.3 boot took 36 million cycles where the real machine takes five. Two things made the disk look still: - The motor stopped as soon as the drive was turned off. The 556 timer of the controller keeps it turning for about a second, as the sequencer card already does, and the writable diskette does not move while stopped. - The diskette gives a nibble on every read, and the 48 0xff sync nibbles of the gap after a sector, where an access ends, read the same sixteen times in a row. The latch of a turning disk is never the same nibble twice: it holds the next one being shifted in, with bit 7 clear. Every other read now gives that, which programs reading nibbles skip. DOS 3.3 reaches its banner in 5.4 million cycles, and the System Master loads Integer BASIC in 4.7 million where it took 59 million, as with the WOZ image on the sequencer card. Tests pin the boot time and check that a diskette INIT formats starts the machine.
2.5 KiB
The headless frontend
headless has no window and no screen. It builds the machine, leaves it
paused and gives you a prompt to drive it: run so many cycles, type something,
print the text screen, save a snapshot. It is the frontend for a script, for a
test, or for looking at what a machine does without watching it happen.
Building
Nothing to install besides Go:
git clone github.com/ivanizag/izapple2
cd izapple2/frontend/headless
go build .
Running
casa@servidor:~$ ./headless
* run 10000
* text
* type 10 PRINT "HELLO WORLD"
* enter
* run 100
* text
* quit
The machine is built with the command line options like
everywhere else, and starts paused. Nothing happens until you say start or
run.
Commands
| Command | What it does |
|---|---|
help |
Prints the list of commands |
quit |
Quits |
start |
Runs the machine at its normal speed, and returns to the prompt while it runs |
pause |
Stops it |
run <cycles> |
Runs <cycles> thousand cycles at full speed and waits until they are done. Only while paused |
cycle |
Prints the cycle count |
reset |
Resets the machine |
key <number> |
Queues a key, as a decimal number from 0 to 127 |
type <text> |
Queues the characters of <text>. No quotes, it can have spaces |
enter |
Queues the Return key. The same as key 13 |
clearkeys |
Empties the key queue |
text |
Prints the text screen on the terminal |
png |
Saves the screen as snapshot.png in NTSC colour |
pngm |
The same in monochrome |
gif |
Records one second of the screen to snapshot.gif, 20 frames of 5 hundredths |
The keys are queued, not typed: they are handed to the machine as it asks for
them, so a type before a run is a fine way to feed a program that is not
running yet.
run is the useful one for a script. It asks for full speed, sets a breakpoint
that many cycles ahead and waits, so a DOS 3.3 boot is over in a moment and the
prompt comes back exactly when it is done. A DOS 3.3 boot from a diskette
spends some five million cycles, so run 10000 covers it.
The help the program prints is ahead of what it does in a few places: there
is no stop (it is pause) and no gifm, and png, pngm and gif take no
arguments, they always write snapshot.png and snapshot.gif.
What is missing
There is nothing to insert a diskette while it runs, and nothing to move the joysticks or press their buttons. Both have to come from the command line, or not at all.