BACKSPACE REACHED THE SHELL. A terminal in line mode does not hand a program every
keystroke: it collects a line, rubs out a backspace, and delivers the finished thing at
Return. CosmOS has always relied on that, and behind a window there is no terminal to do it,
so the raw 0x08 went into the command buffer. Correcting a typo produced a line that looked
perfectly right on the screen and matched no command at all - "I do not know: help".
So the console does it, because behind a window the console IS the terminal. In key mode it
does not, and must not: a program in key mode asked for every keystroke as it happens.
CosmOS now asks for eighty columns at boot. Its own help text is seventy-four characters
wide, and dir, the monitor and the assembler's messages all assume room. The machine still
wakes up in the smaller mode, which is right for a machine - it is the system that knows
what shape of screen its own output needs, and a game that wants forty columns says so.
AND A FILE CAN BE A KEYBOARD, which is the part that matters beyond today. The console
behind a window is not the console behind a terminal, and until now the difference was
unreachable: it broke twice in two days and a person typing found it both times. --keyboard
installs the same hook a window does, so the same path runs, and the manifest has a column
for it. cosmosTyped types "halp", backs over it, arrives at "help", and requires the help to
come out. Verified by removing the rub-out, which loses the whole help text.
It does not test the window. Voyager's key queue and everything about presenting frames are
still out of reach. It tests the console, which is where the logic is.
Along the way: VOY_OBJS was missing from the dependency include, so voyager.o never rebuilt
when a header changed. EmulatorOptions grew a field, Voyager kept an object that disagreed
about the size of the struct, and smashed its stack on every run. A clean build hides it and
'make sanitize' cleans first, so that would never have found it either. Tests/voyager.sh did,
by failing all 115 tests that start the machine - which is the differential test earning its
keep on a bug that has nothing to do with what it was built to check.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW
A tile engine on ports 0x30 to 0x3F, bringing one bank of video memory registered the way
the disk's buffer is. The CPU writes cell indices and the device turns them into pixels,
which is the whole reason a screen is affordable at a megahertz: a frame is 16,667 cycles,
a full 320 by 200 picture is 64,000 bytes, and a 40 by 25 map is 2,000. A program that
changes two cells writes four bytes. The cost of a screen becomes the number of cells that
changed rather than the number of pixels on it.
Which makes colour depth free, so the tiles are eight bits: an 8 by 8 cell is 64 pixels and
each picks independently out of 256 colours, with no per-cell limit of the kind that made a
Spectrum two and C64 multicolour four. The low nibble of a cell's attribute is ADDED to
every index in its tile, sixteen at a time, so a tile drawn in 0 to 15 appears in any of
sixteen schemes without a second copy in tile memory - and a tile wanting all 256 leaves the
nibble at zero and gets them. Neither use costs the other anything.
Two decisions are arithmetic rather than taste, and both come from the machine having no
multiply. A map row is a page whether the mode fills it or not, so a cell address is the row
number as the high byte and the doubled column as the low byte with no arithmetic at all;
otherwise every cursor move on a 40 column screen would cost a row-times-40 in software. And
a palette entry is four bytes rather than three, so entry n is at n times four, a shift.
THE MAP IS A RING and the Scroll register says which of its 128 rows is on top. Scrolling
moves a register and no memory: blitting a 40 by 25 screen up one line is 1,920 bytes inside
one bank, which is twelve percent of a frame even with the controller widened, and a program
printing one page would spend six frames shuffling memory. It is now one port write - and
the rows that scrolled off are still there, which is where a terminal gets scrollback it
never had.
The device is part of the machine rather than part of the window. It renders into a buffer
that is a pure function of video memory, so the same program draws the same picture with
nobody watching; Voyager puts that buffer on the glass and decides nothing. Both binaries
take --screen, which saves a PPM when the machine stops, and that is what makes a screen
checkable on a host with no display at all.
Tests/video.sh checks fourteen named behaviours rather than comparing a recorded image,
because a recorded image would say "something changed" and leave which of the palette, the
tile, the attribute, the map or the scroll register broke to be found by hand. Verified by
breaking three things in turn: the additive nibble failed exactly one check, the scroll
origin exactly two, and moving every cell one pixel sideways exactly the four about
placement.
Tests/docs.sh could not count past nine, which is how a suite of ten scripts reported
itself as wrong for the wrong reason.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW
./SplitBit --disk system.img
stage two
CosmOS
>
No boot image named. The emulator shadows its built in stage one into
Program Memory - boot vector included - and the CPU then does exactly what
it has always done: reads the boot vector and starts where it points.
NOTHING ABOUT THE CPU CHANGED to make a machine that starts itself, which
is what picking shadowing over a mapped ROM bought.
The ROM is generated from Programs/Boot/stage1.asm by the makefile rather
than committed beside it, because a copy of a program kept next to the
program is a copy that goes stale. That makes the assembler a real
dependency of the emulator, which it always sort of was and now says so.
od and awk rather than xxd, which is not everywhere, or python, which the
README does not ask anybody to install in order to build this.
loadROM is loadFile given bytes instead of a path: both go through one
reader over an fmemopen stream, because a ROM is a boot image and there is
no reason for the machine to have two ways of understanding one.
Naming an image still works and is what every other test here does. That
path is not a shortcut to apologise for - placing memory from outside is a
real thing real machines allow, and it is a debugger. The help says so now.
No image and no disk is the one case with nothing to run, and it says that
rather than printing a usage message about a missing file.
run.sh gained a "rom" mode which hands the emulator a disk and nothing
else. The source column still names stage1.asm, because that is what is IN
the ROM: assembling it there says the thing the emulator carries is a thing
that still assembles.
The disk's status has always had a bit meaning "still going", and the header
beside it has always said to honour it. Nothing did, because nothing could: the
host finished the transfer inside the instruction that asked for it, so the bit
could never be seen up and asking about it was asking about something that
cannot happen.
--disk-cycles gives it a latency. The command is still checked at once, because
a refusal is not work - a block that is not there fails before any head moves -
but the transfer is remembered and done when the machine has run that far. Until
then the buffer holds the block BEFORE this one.
That last part is the point. A program that does not wait gets the wrong bytes
rather than an error, which is the failure the bit exists to prevent and the one
that would never have shown up. With a latency of two thousand, CosmOS could not
even mount: sbfsMount reads block zero and looks straight at the buffer.
deviceTick is the general shape rather than a disk feature. Called once per
instruction with the machine's clock, it lets anything whose moment has come
finish - which is what a display that refreshes, or a port that waits on the
host, would want in exactly the same way.
The filesystem watches the bit now, in one small routine reached with RCAL. That
is not decoration: what it hands back is the settled status in A, and CALL puts A
back the way it found it, so an ordinary call cannot carry the one thing this
exists to carry. Two bytes of Stack rather than ten, in a routine that runs on
every block the machine ever touches - the first place in the system where the
new call is the right one rather than merely a cheaper one.
The manifest takes a @N after a disk, the way it already takes :ro, so a test can
ask for a slow one. cosmosSlowDisk lists a directory at two thousand cycles a
block and gets the same listing as everything else, which is the whole assertion:
a filesystem that did not wait would print nonsense rather than fail.
Zero is the default and every other test runs at it. What waiting costs, on a
directory heavy run: 229k cycles at zero, 275k at five hundred, 415k at two
thousand, 1.16M at ten thousand.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW
"Binary" was doing three jobs. It meant an SPBT file that the machine starts
from; it meant whatever the assembler happened to produce, which is now
either that or a loadable program; and it meant a compiled host tool. A word
that means three things means none of them, and the first of the three has a
name already - this project has been calling them boot images for a while
and the manuals had not caught up.
Where it means an SPBT file -> boot image
Where it means either output -> output
Where it means a host executable -> left alone
Where it means base two -> left alone
The user facing messages move with it:
Error: No boot image specified.
Usage: ./SplitBit [OPTIONS] <boot image>
Error: This is not a SplitBit boot image.
Error: This boot image is in format version 2, and this emulator reads 1.
Successfully wrote SplitBit boot image to "hello.bin".
The assembler's own help was the interesting case. Its -o writes either
format, so "the binary" there was never right - it is "the output" now, and
the message that names the format is the one that says which it wrote.
No recorded output contained the word, so nothing needed re-blessing.
Checked before starting rather than after.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW
AnachronautandClaude Opus 5
Anachronaut