One setting to a line: a key, a space, the rest of the line is the value.
A semicolon starts a comment. The format was noticed rather than designed -
textSplit already cuts the first word off a line and leaves the rest, and
textSame already insists two strings end together, so reading a setting is
those two routines and a loop. It is also what the shell reads, which makes
a configuration line a command line the machine reads instead of a person
typing one.
The format was chosen by asking what the BOOT LOADER could manage, because
it is the worst case in every direction: a few kilobytes, no operating
system to report to, and if it fails the machine does not start. Two
formats would be worse than one and the loader cannot have the richer one.
CONFIGURATION IS ADVICE. A missing file, a missing key, an unusable value,
a line too long to read: all of them mean use the default and none is a
failure. BUT QUIET IS NOT SILENT - a setting somebody meant, which did not
take effect, says so. That was the user's addition and it is the better
rule: the default alone leaves the only symptom being that the machine did
not do what somebody asked.
So two routines. cfgGet reads and says nothing, because reading three
settings should not report one bad line three times. cfgCheck reads the
file once and reports, and is handed the caller's list of keys - whether a
key means anything is the only part of this a shared reader cannot judge.
/System/Boot/ holds the boot files, and stage two reads boot.cfg for what
to start, with a fallback to try if it does not work and a name compiled in
for when the file says nothing.
THE TEST FOUND A REAL BUG, and it is the interaction I would not have
thought to look for. First-match-wins met an empty value: a file with
system
system /System/Boot/bare.bin
matched the first line, handed back nothing, and the machine tried to start
a file with no name while a good setting sat underneath. An unusable value
is an absent one - which is what "configuration is advice" says, and this
is where it earns its keep.
cfgBare starts an image with no operating system in it at all, which is
what loading an ordinary boot image buys: a program wanting the whole
machine is a file like any other, chosen the same way the system is. Three
disks differing ONLY in boot.cfg, so each is a test of the file rather than
of the machinery under it.
stage two
CosmOS
> saved it
read it back, 22 bytes:
Stage one hands over to stage two out of a boot slot; stage two mounts the
filesystem, finds /System/cosmos.bin, takes the image apart and places its
code, its data and its vector table, and jumps to the entry point the
vectors named. Nothing placed memory for it.
What it loads is an ORDINARY BOOT IMAGE, the same SPBT file the emulator
has always been handed. That was the user's call and it is the whole trick:
a second stage that loads the machine's normal image format is not a
boot-specific mechanism, so bare metal SplitBit stops being a special case.
A program wanting no operating system under it is just an image, written
under CosmOS like any other, and startable because it is a file.
Three things in it worth knowing:
- THE ENTRY POINT IS CAUGHT ON ITS WAY PAST. Program Memory cannot be read
back, so the boot vector cannot be looked up after being installed; the
vector loop notices the one addressed at 0xFC00 and keeps it.
- A missing "VEC" is not a fault. An image written before vectors existed
simply ends after its data, and then the entry point is zero, which is
what every such image has always relied on.
- Feature flags that are set mean an image asking for a machine this may
not be, and the honest answer to a request that cannot be understood is
to refuse rather than to run it anyway.
The test records that the system WORKS afterwards rather than that it
started. A loaded program running is what says the vector table arrived,
because a program reaches the system through SWI and nothing else; the file
written and the directory entered say the filesystem and the console came
up with it. A second disk has a boot slot and nothing to start, and says so
rather than jumping somewhere.
Anachronaut