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AMD Geode™ LX Processors Data Book 441
Video Processor Register Descriptions
33234H
6.8.3.27 Alpha Window 2 X Position (A2X)
A1T Bit Descriptions
Bit Name Description
63:19 RSVD (RO) Reserved (Read Only). Reads back as 0.
18 PPA1_EN Per-Pixel Alpha Window 1 Enable. Enable per-pixel alpha functionality for alpha win-
dow 1.
0: Single alpha value for entire alpha window 1 (ALPHA1_MUL).
1: Each pixel has its own alpha value defined in the upper 8 bits of the graphics bus.
17 LOAD_ALPHA
(WO)
Load Alpha (Write Only). When set to 1, this bit causes the Video Processor to load the
alpha value (bits [31:24] of the video data path) multiplied with the alpha multiplier bits
(ALPHA1_MUL, bits [7:0]) at the start of the next frame. This bit is cleared by the de-
assertion of VSYNC.
16 ALPHA1_WIN_
EN
Alpha Window 1 Enable. Enable bit for alpha window 1.
0: Disable alpha window 1.
1: Enable alpha window 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) indi-
cates the sign (i.e., increment or decrement). When this value reaches either the maxi-
mum or the minimum alpha value (255 or 0), it keeps that value (i.e., it is not
incremented/decremented) until it is reloaded via LOAD_ALPHA (bit 17).
7:0 ALPHA1_MUL Alpha Window 1 Value. Specifies the alpha value to be used for this window.
VP Memory Offset 0E0h
Typ e R /W
Reset Value 00000000_00000000h
A2X Register Map
63 62 61 60 59 58 57 56 55 54 53 52 51 50 49 48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33 32
RSVD
313029282726252423222120191817161514131211109876543210
RSVD ALPHA2_X_END RSVD ALPHA2_X_START
A2X Bit Descriptions
Bit Name Description
63:28 RSVD (RO) Reserved (Read Only). Reads back as 0.
27:16 ALPHA2_X_
END
Alpha Window 2 X End. Indicates the horizontal end position of alpha window 2. This
value is calculated according to the following formula:
Value = Desired screen position + (H_TOTAL – H_SYNC_END) – 1. (Note 1)
15:12 RSVD (RO) Reserved (Read Only). Reads back as 0.
11:0 ALPHA2_X_
START
Alpha Window 2 X Start. Indicates 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. (Note 1)
Note 1. H_TOTAL and H_SYNC_END are values programmed in the Display Controller module registers.
The value of (H_TOTAL – H_SYNC_END) is sometimes referred to as “horizontal back porch.”