gbos - a tiny Unix-flavored OS for the Game Boy Color (kernel, shell, coreutils in C, RAM filesystem) https://git.sl0p.foo/gbos.git/atom/src/sched.asm?h=master 2026-07-18T20:06:35Z 2026-07-18T20:06:35Z user user@clank 2026-07-18T20:06:35Z urn:sha1:4425150cb6f52d15f513690a75645639358a2030 KEY1 prepare + STOP at KernelInit (skipped on warm reboot if already fast). The PPU/LCD keep their normal rate; the timer and DIV double with the CPU, compensated at the two consumers: - TimerISR now fires at 128 Hz; a toggle byte keeps wTicks at 64 Hz (uptime semantics unchanged) - sys_sleep halves the DIV-delta accumulator's high byte (256 DIV ticks = 1/128 s in double speed) so gsleep/msleep stay real-time Measured: count 60 (scroll-heavy) 3.77s -> 1.89s wall; wTicks 64 Hz over 4s; ping's 800ms msleep pacing unchanged (2.77s for 4 echoes). sl0pboy already emulated KEY1/STOP + per-speed timer/PPU rates. 2026-07-18T08:10:17Z user user@clank 2026-07-18T08:10:04Z urn:sha1:0cc9b0a8bdf774ee376937d5a6767ccdced51245 The kernel had no clock: TimerISR was a reti stub, IEF_TIMER masked, and IME was never enabled - the vectors were decorative. sys_sleep just polls DIV deltas per-process; nothing counted globally. Now: TAC runs the hardware timer at 16384 Hz with TMA=0, so TIMA overflows at exactly 64 Hz; TimerISR increments a monotonic 32-bit wTicks (wraps after ~2.1 years). Scheduling stays cooperative - the ISR is transparent. Enabling IME in a kernel written for zero interrupts needs care wherever SP points into memory whose bank is being switched (an IRQ pushes onto SP): - read_block/write_block map the disk bank over the $A000 window that holds the caller's stack -> di/ei around the transfer (~2ms, well under the 15.6ms tick period, so no tick is ever lost) - hSwitchTo switches SVBK + cart-RAM banks under the outgoing stack -> di on entry, ei once the incoming stack is mapped - fork already runs on KSTACK_TOP2 (fixed WRAM) - safe as-is - term_putc's SVBK switch only remaps $Dxxx, stacks live in $Axxx/$Cxxx SYS_UPTIME (36) copies the counter (4B LE, di/ei so the read can't tear) to a user buffer; libc gticks(); usr/uptime.c formats 'up [Nd] H:MM:SS'. uptime avoids SDCC long div/shift entirely: sm83.lib modules link into their own areas that land in the $A000 RAM window (latent build.sh trap, documented there) - bytewise >>6 plus bounded subtraction loops instead. 2026-07-15T22:12:43Z user user@clank 2026-07-15T22:12:43Z urn:sha1:19a2b63bab71b796ee456b3ae8bec1a2ab297158 - exit(): zombie + status, reparent orphans to init, wake blocked parent, schedule away forever (resources reclaimed by the reaper) - wait(): scan for a zombie child; reap (free cart-RAM bank + PCB slot) and return pid/code; block PS_BLOCKED + yield if children still live; $FF if none - cart-RAM banks are now a free list (wBankUsed bitmap): AllocRamBank/FreeRamBank - scheduler: FindNextReady returns carry when nothing runnable; yield idles instead of blindly picking slot 0 - helpers: FindPcbByPid, ReparentToInit - demo: init forks 3 workers -> exec -> exit(pid) -> wait/reap => wwwR2R3R4! verified bank recycling with 6 workers over 3 banks (w2w3w4w5w6w7) - README: document the lifecycle + syscall status 2026-07-15T21:44:28Z user user@clank 2026-07-15T21:44:28Z urn:sha1:de725da74db5cba0f9bfd0755269e1683423d87b - fix ClearKernelRAM clobbering the kernel stack (only clear $C000-$CBFF) - fix SyscallTrap clobbering DE (buffer arg) during table dispatch - README: run via ~/dev/gbc --headless; note bring-up bugs