AMD SC1201, SC1200 manual 3118, Decremented until it is reloaded via bit 17 Loadalpha

Video Processor Module - Video Processor Registers - Function 4 32579B

Table 7-9. F4BAR0+Memory Offset: Video Processor Configuration Registers (Continued)

Bit

Description

Offset 68h-6Bh		Alpha Window 1 Color Register (R/W)	Reset Value: 00000000h
31:25	Reserved.

24ALPHA1_COLOR_REG_EN (Alpha Window 1 Color Register Enable). Enable bit for the color key matching in Alpha Window 1.

	1: Enable. If this bit is enabled and the alpha window is enabled, then where there is a color key match. The color value (in
	bits [23:0], ALPHA1_COLOR_REG) is displayed.
	0: Disable. Where there is a color key match, no blending is performed.
23:0	ALPHA1_COLOR_REG (Alpha Window 1 Color Register). Specifies the color to be displayed inside Alpha Window 1
	when there is a color key match in the alpha window. This is an RGB value (for RGB blending) or a YUV value (for YUV
	blending). In interlaced YUV blending mode, Y/2 value should be used.
	This color is only displayed if the alpha window is enabled and bit 24 (ALPHA1_COLOR_REG_EN) is enabled.
Offset 6Ch-6Fh		Alpha Window 1 Control Register (R/W)	Reset Value: 00000000h
31:18	Reserved.

17LOAD_ALPHA (Load Alpha Value). (Write Only) When set to 1, this bit causes the Video Processor to load the alpha value (in bits [7:0], ALPHA_VAL) at the start of the next frame.

16ALPHA1_WIN_EN (Alpha Window 1 Enable). Enable bit for Alpha Window 1.

1:Enable Alpha Window 1.

0: Disable Alpha Window 1.

	Note:	Valid only if video window is enabled (F4BAR0+Memory Offset 00h[0] = 1).
15:8	ALPHA1_INC (Alpha Window 1 Increment). Specifies the alpha value increment/decrement. This is a signed 8-bit value
	that is added to the alpha value for each frame. The MSB (bit 15) indicates the sign (i.e., increment or decrement). When
	this value reaches either the maximum or the minimum alpha value (255 or 0) it keeps that value (i.e., it is not incremented/
	decremented) until it is reloaded via bit 17 (LOAD_ALPHA).
7:0	ALPHA1_VAL (Alpha Window 1 Value). Specifies the alpha value to be used for this window.
Offset 70h-73h		Alpha Window 2 X Position Register (R/W)	Reset Value: 00000000h

Note: H_TOTAL and H_SYNC_END are values programmed in the GX1 module’s Display Controller Timing registers (GX_BASE+Memory Offset 8330h[26:19] and 8338h[10:3], respectively). The value of (H_TOTAL – H_SYNC_END) is some- times referred to as “horizontal back porch”. For more information, see the AMD Geode™ GX1 Processor Data Book.

Desired screen position should not be outside a video window (F4BAR0+Memory Offset 08h and 0Ch).

31:27		Reserved.
26:16		ALPHA2_X_END (Alpha Window 2 Horizontal End). Determines the horizontal end position of Alpha Window 2 (not inclu-
		sive). This value is calculated according to the following formula:
		Value = Desired screen position + (H_TOTAL – H_SYNC_END) – 1.
15:11		Reserved.
10:0		ALPHA2_X_START (Alpha Window 2 Horizontal Start). Determines the horizontal start position of Alpha Window 2. This
		value is calculated according to the following formula:
		Value = Desired screen position + (H_TOTAL – H_SYNC_END) – 2.
Offset 74h-77h			Alpha Window 2 Y Position Register (R/W)	Reset Value: 00000000h
Note:	V_TOTAL and		V_SYNC_END are values programmed in the GX1 module’s	Display Controller Timing registers
	(GX_BASE+Memory Offset 8340h[26:16] and 8348h[26:16], respectively). The value of (V_TOTAL – V_SYNC_END) is some-
	times referred to as “vertical back porch”. For more information, see the AMD Geode™ GX1 Processor Data Book.
	Desired screen position should not be outside a video window (F4BAR0+Memory Offset 08h and 0Ch).
31:27		Reserved.
26:16		ALPHA2_Y_END (Alpha Window 2 Vertical End). Determines the vertical end position of Alpha Window 2 (not inclusive).
		This value is calculated according to the following formula:
		Value = Desired screen position + (V_TOTAL – V_SYNC_END) + 2.
15:11		Reserved.
10:0		ALPHA2_Y_START (Alpha Window 2 Vertical Start). Determines the vertical start position of Alpha Window 2. This value
		is calculated according to the following formula:
		Value = Desired screen position + (V_TOTAL – V_SYNC_END) + 1.
AMD Geode™ SC1200/SC1201 Processor Data Book				347