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| author | user <user@clank> | 2026-07-18 10:10:04 +0200 |
|---|---|---|
| committer | user <user@clank> | 2026-07-18 10:10:17 +0200 |
| commit | 0cc9b0a8bdf774ee376937d5a6767ccdced51245 (patch) | |
| tree | 221326e7a86fa0121ae7eea1763a9f3ffa8100e6 /src/blk.asm | |
| parent | kernel: dmesg-style boot spew before init spawns (diff) | |
| download | gbos-0cc9b0a8bdf774ee376937d5a6767ccdced51245.tar.gz gbos-0cc9b0a8bdf774ee376937d5a6767ccdced51245.tar.xz gbos-0cc9b0a8bdf774ee376937d5a6767ccdced51245.zip | |
kernel: a real timer source (64 Hz tick IRQ) + uptime(1)
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.
Diffstat (limited to '')
| -rw-r--r-- | src/blk.asm | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/src/blk.asm b/src/blk.asm index 2be961e..76561da 100644 --- a/src/blk.asm +++ b/src/blk.asm @@ -34,6 +34,8 @@ ENDM ; ----------------------------------------------------------------------------- read_block:: ld c, a + di ; the tick ISR pushes on SP, which points into + ; the $A000 window we are about to remap srl a srl a srl a @@ -54,6 +56,7 @@ read_block:: dec b jr nz, .cp restore_bank ; inline - no stack while the disk bank is mapped + ei ret ; ----------------------------------------------------------------------------- @@ -61,6 +64,7 @@ read_block:: ; ----------------------------------------------------------------------------- write_block:: ld c, a + di ; see read_block srl a srl a srl a @@ -81,6 +85,7 @@ write_block:: dec b jr nz, .cp restore_bank + ei ret ; ============================================================================= |