jetpac: Routine at 631c

631c: The main game loop.

This routine is called until a new item/alien is generated, then 6310 is called.

Used by the routines at 6310, 692e and 6971.

Input
IX	address of main jump table

631c

ld a,($5c78)

Compare SYSVAR_FRAMES and last_frame

631f

ld c,a

6320

ld a,($5dd4)

6323

cp c

Note: if we have EI here, then 692e will be called and DI executed.

6324

call nz,$692e

If they're not equal, do frame update

When one of the `main_jump_table` update routines RETurns, the new game actor routine will be called.

6327

ld hl,$6971

HL=generate new actor routine

632a

push hl

...and push `ret` address to the stack.

Execute one of the update routines using the value in IX.

632b

ld hl,$633d

HL=main jump table

632e

ld a,(ix+$00)

Calculate the jump table offset

6331

rlca

6332

and $7e