Differences

This shows you the differences between two versions of the page.

--- interrupt_scheduler [2016/05/31 23:09]
ex_writer [ACTINT]
+++ — (current)
@@ Line 1: / Line 1: @@
-====== Interrupt Scheduler ======
-The Interrupt Scheduler handles system timers and counters.
-===== Interrupt Scheduler Routines =====
-^ Name ^ Description ^
-| [[interrupt scheduler#actint|ACTINT]] | Activate automatic interrupt service (timers, music, blackout) |
-| [[interrupt scheduler#ctimer|CTIMER]] | Call custom timer |
-| [[interrupt scheduler#deccts|DECCTS]] | Decrement counters/timers under mask (used by ACTINT and DECCTS) |
-| [[interrupt scheduler#stimer|STIMER]] | Track and decrement game timers |
-===== Interrupt Scheduler Routine Descriptions =====
-==== ACTINT ====
-ACTIVE INTERRUPTS
-| Calling Sequence: | <code z80>SYSTEM    ACTINT</code> or <code z80>SYSSUK    ACTINT</code>|
-| Arguments: | None |
-| Outputs: | None |
-| Description: | ACTINT provides automatic interrupt service and runs the seconds timer, the game timer, the music processor, and blackout timers, plus CT0–CT3. |
-| Notes: | Timers function every 1/60<sup>th</sup> of a second. |
-Once ACTINT is called, it sets:
-  * Z80 Interrupt mode 2 (IM 2)
-  * INLIN = 200 (line 100)
-  * I register and Interrupt Feedback (INFBK)
-  * Enable interrupts (EI)
-ACTINT also calls TIMEX and TIMEY which decrement counters/timers.
-==== CTIMER ====
-CUSTOM TIMER
-| Calling Sequence: | <code z80>CALL      CTIMER</code>|
-| Input: | HL = address of custom time base\\ B = value to load into time base 1 to 0 transition\\ C = counter mask as in [[interrupt scheduler#deccts|DECCTS]] |
-| Description: | HL is loaded and decremented. If HL != 0, then a return is executed, otherwise, HL is loaded with B and [[interrupt scheduler#deccts|DECCTS]] is called.\\ Registers HL, DE, BC, and AF are undefined upon exit. |
-==== DECCTS ====
-DECREMENT COUNTERS/TIMERS
-| Calling Sequence: | <code z80>SYSTEM    DECCTS</code> or <code z80>SYSSUK    DECCTS
-DB        (mask)</code>|
-| Arguments: | C = mask for which counters to decrement |
-| Outputs: | [[human interface#sentry|SENTRY]] will notify the program |
-| Description: | Decrements counter if they are non-zero. If any counters go from 1 to 0, [[human interface#sentry|SENTRY]] is notified. |
-==== STIMER ====
-DECREMENT TIMERS
-| Calling Sequence: | <code z80>PUSH      AF
-PUSH      BC
-PUSH      DE
-PUSH      HL
-CALL      STIMER
-POP       HL
-POP       DE
-POP       BC
-POP       AF</code>|
-| Input: | None |
-| Description: | STIMER keeps track of game time. If it hits 0, then bit 7 (GSBEND, i.e., game end) in the game status byte (GAMSTB) is set. |
-| Uses: | AF, BC, DE, HL |
-| Calls: | Music processor on note (duration) expiration |
-| Note: | Sets bit 7 of KEYSEX (KEYS-EX tracking byte) to 1 on every second |