Synopsis #

Header: fxcg/display.h (Not yet in libfxcg)
Syscall index: 0x091E
Function signature: unsigned short Bdisp_FrameAndColor(int action,unsigned short flags);

Parameters #

actions

• If action == 0 clear the internal flags.
• If action == 1 Take action based upon the internal flags and then clear the internal flags.
• If action == 2 Set the internal flags to 0x8000.
• If action == 3 Or the value of flags (the parameter not the internal variable) with 0x8000 and set the internal variable.
• Other values of action just cause the function to return see #returns.

Possible flag values (this applies both to the parameter and the internal variable flags):

• bit 15 If set allows the function to carry out other actions as determined by other flags when action == 1
• bit 4 If set enable 16-bit color mode, otherwise enable 8 color mode
• bit 0 If set draw a black frame, otherwise draw a white frame.

Returns #

The final value of it’s internal flags.

Comments #

Here is a disassembly of the function:

Bdisp_FrameAndColor:
        sts.l   pr, @-r15
        tst r4, r4
        bt  clearFlags  ! Branch if R4 is zero
        mov r4, r0
        cmp/eq  #1, r0
        bt  R4One
        cmp/eq  #2, r0
        bt  R4Two
        cmp/eq  #3, r0
        bt  R4Three
        bra exit
        nop
! ---------------------------------------------------------------------------

R4One:
        mov.l   #frameAndColorFlags, r1
        mov.w   #0xFFFF8000, r6
        extu.w  r6, r6      ! r6 = 32768
        mov.w   @r1, r0
        tst r6, r0      ! Is bit 15 clear?
        bt  exit        ! If so branch without a delay
        tst #16, r0
        mov.l   #Bdisp_SetDDRegisterB, r2
        bt/s    bit4Clear   ! Branch if bit 4 is clear
        mov #0, r4      ! If bit 4 is clear set r4 to 0
        mov #1, r4      ! Otherwise set it to one

bit4Clear:
        jsr @r2     ! Bdisp_SetDDRegisterB
        nop
        mov.l   #frameAndColorFlags, r1
        mov.l   #DrawFrameC3, r2
        mov.w   @r1, r0
        tst #1, r0
        bt  whiteFrame  ! Branch if bit 0 is clear
        jsr @r2 ! DrawFrameC3
        mov #0, r4      ! Black frame
        bra clearFlags
        nop
! ---------------------------------------------------------------------------

whiteFrame:
        jsr @r2 ! DrawFrameC3
        mov #7, r4

clearFlags:
        mov.l   #frameAndColorFlags, r1
        mov #0, r2
        bra exit
        mov.w   r2, @r1
! ---------------------------------------------------------------------------

R4Two:
        mov.l   #frameAndColorFlags, r1
        mov.w   #0xFFFF8000, r6
        bra exit
        mov.w   r6, @r1
! ---------------------------------------------------------------------------

R4Three:
        mov.l   #frameAndColorFlags, r1
        mov.w   #0xFFFF8000, r6
        or  r6, r5
        mov.w   r5, @r1

exit:
        mov.l   #frameAndColorFlags, r1
        lds.l   @r15+, pr
        rts
        mov.w   @r1, r0
! End of function Bdisp_FrameAndColor