WonderWitch/FreyaBIOS/System

The System interrupt provides assorted system-related functionality.

Interrupts

INT $17/AH=$00 - sys_interrupt_set_hook

• AH = $00
• AL = Interrupt index
• DS:BX = Pointer to new vector (read from)
• DS:DX = Pointer to old vector (written to)

INT $17/AH=$01 - sys_interrupt_reset_hook

• AH = $01
• AL = Interrupt index
• DS:BX = Pointer to old vector (read from)

INT $17/AH=$02 - sys_wait

• AH = $02
• CX = Frames to wait

INT $17/AH=$03 - sys_get_tick_count

• AH = $03

Return:

• DX:AX = Number of frames since system start

INT $17/AH=$0A - sys_get_ownerinfo

• AH = $0A
• DS:DX = Output buffer
• CX = Output buffer size, in bytes

Errata:

• The FreyaBIOS implementation only works correctly in the "mono" mode. An alternate implementation that supports "color" mode is provided as part of libwwc.

INT $17/AH=$0B - sys_suspend

• AH = $0B
• AL = Suspend slot (see below)
• DS:BX = Pointer to I/O resume table (see below)

Return:

• AX = 0 if suspend successful, 1 if returning from suspend (via sys_resume).

Makes a copy of the execution state (IRAM, I/O ports, stack) to be restored via sys_resume (see below).

Suspend/resume structure

This structure is stored in SRAM block 3, offset $7E00 (slot 1) and $BF00 (slot 0).

Offset	Size	Contents
$0000	16384	Copy of RAM area $0000 - $3FFF
$4000	4	Far pointer to I/O resume table (DS:BX), plus 1
$4004	224	Copy of IO ports $00 - $DF
$40E4	2	Value of CX?
$40E6	2	Value of SP?
$40E8	2	Value of SS?

In addition, these SRAM block 3 locations are used:

Offset	Contents
$FFEE	Resumable status for slot 0 (bit 7 = resumable?, bit ?..0 = ID)
$FFEF	Resumable status for slot 1 (bit 7 = resumable?, bit ?..0 = ID)

I/O resume table

Offset	Size	Contents
$00	2	'IO'
$02	224	Resume configuration for each I/O port

INT $17/AH=$0C - sys_resume

• AH = $0C
• AL = Suspend slot?

Resumes execution from an existing suspend slot. Returns to where sys_suspend was last called, but with a different return value.

INT $17/AH=$12 - sys_get_version

• AH = $12

Return:

• AX = BIOS version

INT $17/AH=$14 - sys_set_resume

• AH = $14
• BL = Resumable flag for slot ?
• BH = Resumable flag for slot ?

INT $17/AH=$15 - sys_get_resume

• AH = $14

Return:

• AL = Resumable flag for slot ?
• AH = Resumable flag for slot ?