CosmOS had 1,161 bytes of Program Memory left before the address applications
load at, and Tab completion is not going to fit in that with anything to spare.
So the wall moves up one page: the system keeps below 0x4FFF and 0x2FFF, and an
application is based at 0x5000 and 0x3000.
A PAGE IS A CHEAP THING TO GIVE IT AND AN EXPENSIVE THING TO RUN OUT OF. An
application still has 44K of Program Memory before the vector table and the
largest one here uses 7.5K, so what was taken from applications is space nothing
has ever asked for - while what the system gained is the difference between
building the next thing and counting bytes while building it.
Not doubling, which was the version that would have cost application space worth
minding. One page, and the same again when it is needed.
Nothing in the machine knows where the wall is, so this is 34 #Base lines, one
threshold in the fault handler, and the table in the CosmOS README that
Tests/docs.sh reads its limits out of.
The native assembler's scratch map had to move with it, and docs.sh said so
before anything ran: its data reached 0x40D6 and its buffers began at 0x4000, so
they were sitting on its variables. That file already carries a paragraph about
the floor coming up and the map staying where it was. It has happened twice now,
and been caught by a check the first time wrote.
Twenty three recordings are the same runs a page higher.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW
A five instruction program that writes one port and exits has no Data Segment at
all, and the loader stopped the machine dead on it. It asked the memory
controller to move a segment of no bytes, and a length of zero asks for the
whole 64K - which is the machine's rule, and a reasonable one, since two bytes
cannot say 65536 and a transfer of nothing is not usually what anybody meant. It
is exactly what was meant here. 64K did not fit, the controller refused, and the
load stopped half done.
ON A TERMINAL THAT PRINTS A FAULT WITH AN ADDRESS. Behind a window it is a
frozen picture and no reason at all, which is how it was found and is a separate
problem from this one.
The header says how long each segment is, so the loader knows before it asks.
Both bytes are already in hand, so the test costs one OR. Nothing is lost by
skipping the transfer: a blit leaves the controller's addresses past whatever it
touched, and a blit of nothing would have left them where they already are,
which is where the vectors are read from next.
Guarded for the code segment too. A program with no code is equally assemblable
and would have stopped in exactly the same place.
Mode.sbx is the fix's test and a program worth having on its own: forty columns
or eighty, whichever the screen is not in, which is what a person wanting Snake
drawn twice the size actually needs. Ten instructions and no data, deliberately
- it prints its two digits a register at a time rather than from a string, so it
stays the smallest shape a loadable program can take. Nothing else on that disk
had ever been that shape, which is why nothing had ever tried it.
Reported by the user, who wrote the program.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW
AnachronautandClaude Opus 5