Bt848 Software Specification
Hardware Interfaces
6
UG848_3A
Bt848
Software Specification
Brooktree
®
Hardware Interfaces
There are three major hardware interfaces between the Bt848 device and its driver software:
•
Video Decoder
•
Video Scaler
•
DMA Controller
The video decoder and scaler have independent control of the odd and even fields. The DMA
controller receives separate commands for each field. Other major interfaces to the driver software
are the Plug and Play™ interface and the Direct Draw Interface. Figure 3 shows the relationships
between the different interfaces.
The video decoder block of the Bt848 is programmed during the capture/preview initialization
process. After that point, there are infrequent changes, such as setting a desired color format, bright-
ness, hue, etc. The video scaler on the other hand will be programmed quite frequently to support
video in a window functionality. The scaler parameters will be changed every time the user has
changed the dimensions or the position of the preview window.
The Bt848 DMA controller executes the RISC instructions generated by the driver software.
The RISC instruction sequence may be changed due to several reasons, for example when there has
been a change in the graphics overlayed on the video window. Another example is when there have
been changes in the destination addresses for both capture (every field) and preview (when the win-
dow has been moved or resized). Changes to the RISC instruction sequence involve adding or
removing commands for an entire field. The RISC program cannot be changed on a per line basis.
Figure 3. Bt848 Capture Driver Interfaces
Bt848 Capture Driver
Direct Draw
Plug and Play
and VxD
Decoder
Scaler
DMA
Controller
Bt848
