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Ilia Sharin 2026-04-26 14:46:18 -04:00
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10
10_devices/timer.md
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@ -122,7 +122,7 @@ The **E-clock** is derived from the system clock ÷ 10:
### VBlank Timing
UNIT_VBLANK is synchronised to the display's vertical blank interrupt:
UNIT_VBLANK is synchronized to the display's vertical blank interrupt:
| Standard | VBlank Rate | Period | Use |
|---|---|---|---|
@ -155,7 +155,7 @@ struct EClockVal { /* OS 2.0+ */
---
## Proper Initialisation and Shutdown
## Proper Initialization and Shutdown
timer.device uses the standard Exec I/O model: a **MsgPort** for signal delivery, an **IORequest** to describe the operation, and an explicit **open/close** lifecycle. Every step matters — skipping any one causes subtle or catastrophic failures.
@ -191,8 +191,8 @@ struct Library *TimerBase = (struct Library *)tr->tr_node.io_Device;
|---|---|
| Skip `CreateMsgPort` | No signal bit allocated → `Wait()` will never wake up. Or worse: signal bit 0 (CTRL-C) gets reused, causing random task termination. |
| Skip error check on `CreateIORequest` | NULL IORequest passed to `OpenDevice` → immediate crash (NULL pointer dereference in Exec). |
| Skip `OpenDevice` error check | If device can't open (e.g. wrong unit), the IORequest is uninitialised — any subsequent `DoIO`/`SendIO` writes to random memory → Guru Meditation. |
| Use `AllocMem` instead of `CreateIORequest` | IORequest fields (`io_Message.mn_ReplyPort`, `io_Message.mn_Length`) are not initialised → device replies to garbage address → memory corruption. |
| Skip `OpenDevice` error check | If device can't open (e.g. wrong unit), the IORequest is uninitialized — any subsequent `DoIO`/`SendIO` writes to random memory → Guru Meditation. |
| Use `AllocMem` instead of `CreateIORequest` | IORequest fields (`io_Message.mn_ReplyPort`, `io_Message.mn_Length`) are not initialized → device replies to garbage address → memory corruption. |
| Not saving `TimerBase` | Can't call `AddTime`/`SubTime`/`CmpTime`/`ReadEClock` — they require the device's library base in A6. |
### Shutdown (The Right Way)
@ -311,7 +311,7 @@ if (timerPending)
## Use Case 3: Game/Demo Frame Sync (Periodic Timer)
```c
/* 50 Hz game loop synchronised to PAL frame rate: */
/* 50 Hz game loop synchronized to PAL frame rate: */
#define FRAME_USEC 20000 /* 1/50th second = 20ms */
void GameLoop(void)