USER subroutine: Difference between revisions
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The USER subroutine (not called, always jumped to by the BIOS) is required | The USER subroutine (not called, always jumped to by the BIOS) is required [[68k]] code which needs to perform actions according to the command value set in {{BR|BIOS_USER_REQUEST}}. | ||
At the end of the routine, a jump to BIOSF_SYSTEM_RETURN is needed to give back control to the BIOS. | At the end of the routine, a jump to [[SYSTEM_RETURN|BIOSF_SYSTEM_RETURN]] is needed to give back control to the BIOS. | ||
=Handling code= | |||
<syntaxhighlight> | |||
JT_User: | |||
dc.l StartupInit | |||
dc.l EyeCatcher | |||
dc.l Game | |||
dc.l Title | |||
User: | |||
move.b d0,REG_DIPSW | |||
clr.l d0 | |||
move.b BIOS_USER_REQUEST,d0 | |||
lsl.b #2,d0 | |||
lea JT_User,a0 | |||
movea.l (a0,d0),a0 | |||
jsr (a0) | |||
jmp BIOSF_SYSTEM_RETURN | |||
</syntaxhighlight> | |||
=USER_REQUEST values= | =USER_REQUEST values= | ||
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Initilization of the soft/debug [[DIPs]] in the [[68k user RAM]]. Used only once, when the game is started for the first time on a MVS system (probably when the BIOS doesn't find the game's NGH number in the [[backup RAM]]). | Initilization of the soft/debug [[DIPs]] in the [[68k user RAM]]. Used only once, when the game is started for the first time on a MVS system (probably when the BIOS doesn't find the game's NGH number in the [[backup RAM]]). | ||
Set BIOS_USER_MODE to 0 during operations, and don't forget to kick the watchdog as interrupts are disabled. | Set {{BR|BIOS_USER_MODE}} to 0 during operations, and don't forget to kick the watchdog as interrupts are disabled. | ||
Initilization of the rest of the user RAM, the display, and I/O. | Initilization of the rest of the user RAM, the display, and I/O. | ||
Viewpoint, which has its backup RAM save pointer set to $100000 (header $10E) and game save size set to $0200 (header $112) does this: | [[Viewpoint]], which has its backup RAM save pointer set to $100000 (header $10E) and game save size set to $0200 (header $112) does this: | ||
<syntaxhighlight> | <syntaxhighlight> | ||
move.b #$00,BIOS_USER_MODE | move.b #$00,BIOS_USER_MODE | ||
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==Command 3== | ==Command 3== | ||
Show the game's title screen. This is called when a coin is inserted on MVS systems. | Show the game's title screen. This is called when a coin is inserted on [[MVS systems]]. | ||
{{BR|BIOS_COMPULSION_TIMER}} is used as a count-down timer for auto-start. | {{BR|BIOS_COMPULSION_TIMER}} is used as a count-down timer for auto-start. | ||
[[Category:Code]] | [[Category:Code]] | ||
Revision as of 18:03, 5 January 2014
The USER subroutine (not called, always jumped to by the BIOS) is required 68k code which needs to perform actions according to the command value set in BIOS_USER_REQUEST ($10FDAE ) .
At the end of the routine, a jump to BIOSF_SYSTEM_RETURN is needed to give back control to the BIOS.
Handling code
JT_User:
dc.l StartupInit
dc.l EyeCatcher
dc.l Game
dc.l Title
User:
move.b d0,REG_DIPSW
clr.l d0
move.b BIOS_USER_REQUEST,d0
lsl.b #2,d0
lea JT_User,a0
movea.l (a0,d0),a0
jsr (a0)
jmp BIOSF_SYSTEM_RETURNUSER_REQUEST values
Command 0
Initilization of the soft/debug DIPs in the 68k user RAM. Used only once, when the game is started for the first time on a MVS system (probably when the BIOS doesn't find the game's NGH number in the backup RAM).
Set BIOS_USER_MODE ($10FDAF ) to 0 during operations, and don't forget to kick the watchdog as interrupts are disabled.
Initilization of the rest of the user RAM, the display, and I/O.
Viewpoint, which has its backup RAM save pointer set to $100000 (header $10E) and game save size set to $0200 (header $112) does this:
move.b #$00,BIOS_USER_MODE
lea $100000,a0 ;Start of game save block
move #$001F,d1 ;32*4 longword writes = 512 bytes
moveq #0,d0
.cl:
move.l d0,(a0)+
move.l d0,(a0)+
move.l d0,(a0)+
move.l d0,(a0)+
dbf d1,.cl
move.b d0,REG_WATCHDOG
...
jmp BIOSF_SYSTEM_RETURNCommand 1
Show the game's own boot logo animation (when $114 = 1).
More information needed (end flag, BIOS_USER_MODE value ?).
Command 2
Show the game's demo (the recommended duration is ?).
Command 3
Show the game's title screen. This is called when a coin is inserted on MVS systems. BIOS_COMPULSION_TIMER ($10FDDA ) is used as a count-down timer for auto-start.