AMD Geode LX 800@0.9W - Manual (Page 444)

444 AMD Geode™ LX Processors Data Book
Video Processor Register Descriptions 33234H
6.8.3.31 Alpha Window 3 X Position (A3X)
16 ALPHA2_WIN_
EN Alpha Window 2 Enable. Enable bit for alpha window 2.
0: Disable alpha window 2.
1: Enable alpha window 2.
15:8 ALPHA2_INC Alpha Window 2 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 ALPHA2_MUL Alpha Window 2 Value. Specifies the alpha value to be used for this window.
VP Memory Offset 100h
Type
R/W
Reset Value 00000000_00000000h
A2T Bit Descriptions (Continued)
Bit Name Description
A3X 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
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
RSVD ALPHA3_X_END RSVD ALPHA3_X_START
A3X Bit Descriptions
Bit Name Description
63:28 RSVD (RO) Reserved (Read Only). Reads back as 0.
27:16 ALPHA3_X_
END Alpha Window 3 X End. Indicates the horizontal end position of alpha window 3. 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 ALPHA3_X_
START Alpha Window 3 X Start. Indicates the horizontal start position of alpha window 3. 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.”