Broadcom BCM7405, General Information Manual

Page: 59 / 194

2/24/2008 9T6WP
Preliminary Hardware Data Module BCM7405
06/29/07
Functional Description
Bro a d c o m Co rp o r a ti o n
Document 7405-1HDM00-R Video and Graphics Display Page 1-45
Compositor Block Diagram
Figure 1-10 shows the system architecture of the Memory-to-Memory Compositor architecture. As depicted, the Memory-to-
Memory Compositor consists of a collection of smaller, independent blocks. Specifically, there would be two feeders to
access DRAM, a scaler that would handle any scale size (as well as filtering operations), a compositor to allow blending, a
ROP generator, and a capture block.
Figure 1-10: Memory-to-Memory Compositor Block Diagram
Scaler Overview
The scaler is the heart of the compositor architecture. It is responsible for all scaling functions as well as any filtering. The
goal is to allow anti-flutter filtering for graphics to occur in the Compositor to free up real-time memory bandwidth and to save
the silicon area required for the line stores. Another benefit is to allow higher quality filtering than one or two line stores would
allow.
To store a horizontal line would require 2048 x 32-bpp or 64 Kbits. To allow a horizontal line-averaging filter, two of these
line stores would be required totaling 128 Kbits. By using a vertical stripping algorithm, eight line stores—each holding 128
32-bit pixels—would only take 32 Kbits worth of storage.
While the vertical stripe uses less SRAM storage, it does require more bandwidth. This is due to having to reread (overlap)
data so that the filtering can be performed. Without this overlapping, visible seams would appear. To balance the extra
bandwidth (and reduce the number of stripes), the internal buffers could be increased to 64 Kbits or larger without altering
the architecture.
Figure 1-11 shows and example of the stripe parameters.
The goal of this scaler is to allow any-to-any scaling combination to be performed with one pass through the compositor.
This single pass may not result in the highest visual quality. If higher scaling quality is required, multiple passes may be
required through the compositor.
S
2D
Scaler
ROP
Comp
S
Source Feeder. Accepts YUV4:2:2, ARGB8888, 4444, 1555, 0565, CLUT1/2/4/8 data, supplies ARGB8888 data
D
B
3rd input source for ROP functions only. This is an 8x8 bitmap for Windows support
D
Dest. Feeder. Accepts YUV4:2:2, ARGB8888, 4444, 1555, 0565, CLUT1/2/4/8 data, supplies ARGB8888 data
C
B
C
Capture Block. Accepts ARGB8888 data and supplies ARGB8888, 4444, 1555, or AYUV8888, YUV422 (?)
supplies ARGB8888 data