Reboot, and the machine device that makes it possible

Until now the only way to restart was to stop the emulator and run it again, which meant the one thing the machine could not do was the thing Once was written for. The loop now closes without leaving it: > Once /System/Boot/bare.bin next start: /System/Boot/bare.bin, once > Reboot starting again stage two just this once: /System/Boot/bare.bin bare metal: no system, just this Writing 1 to port 0x13 asks the machine to start over. A PORT RATHER THAN A SERVICE, because a reset has to work when the system does not: something only askable through SWI would be unavailable in exactly the case that wants it most, and a program that owns the whole machine has no system to ask. It is device class 0x04, in the range kept for the machine rather than among the peripherals, because it is not one - it is not attached to anything and cannot be unplugged. WHAT A RESET REPEATS IS HOW THE MACHINE STARTED. Named an image, the emulator places it again; named none, the ROM is shadowed again and reads the disk. Anything else would mean a reset changed what the machine IS, which is the one thing a reset must not do. Both are tested. Taken between instructions, because a device cannot restart the machine from inside the instruction that asked: the CPU is part way through a step and its state is not yet anything a reset could leave behind consistently. The disk stays attached and keeps everything written to it - that is what warm means. The vector table is cleared, which is the one deliberate departure from leaving memory alone: a vector points into whatever installed it, and after a reset that program is not running, so a handler left behind would aim an interrupt at an address belonging to something gone. It is the argument CosmOS already makes at exit, applied to the machine. Reboot is 45 bytes, most of them the word it prints.
2026-08-27 20:56:46 -04:00
parent 7b28f48f52
commit 79727044b7
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+; Reboot.asm
+; Starts the machine again.
+;
+; Whatever put the first instruction in memory does it again, and everything after that
+; follows: the boot slot is read, the loader runs, and whatever the configuration names -
+; or whatever Once asked for - is what starts.
+;
+; ---- Why this writes a port ----
+;
+; A reset has to work when the system does not. Something that could only be asked for
+; through SWI would be unavailable in exactly the case that wants it most, and a program
+; that owns the whole machine has no system to ask. So the machine takes it directly, the
+; way it takes everything else: a byte out of a port.
+;
+; It is still a program rather than a shell word, because it is not the shell's business
+; and because a word built into the shell is not callable by anything else.
+;
+; ---- What survives ----
+;
+; The disk, and everything written to it. That is what warm means: the machine starts
+; again, the world it starts into does not. Nothing here flushes anything, because nothing
+; on this machine is held back - a file is on the disk when the write returns.
+;
+; Written by Anachronaut
+
+#Include services.asm
+
+#Program
+
+  #Base 0x4000
+
+start:
+  SETD.0 Saying
+  SWI osPrintString
+
+  INIA 0x01
+  OUTA 0x13
+
+  ; Not reached. The machine has started over by the time the next instruction would run,
+  ; so anything here is a statement about a machine that no longer exists - but a program
+  ; whose last instruction is an output is one byte from running into whatever follows it,
+  ; and that is not a habit worth keeping.
+  RSTA
+  SWI osExit
+
+#Data
+
+  #Base 0x2000
+
+Saying:
+"starting again
+"