
Channel Buffer Controller
6-51
The Channel Buffer Controller has other features that aid the host in
system operation. These features include the ability to reset each of the
buffers individually, support for extracting an actual decode time stamp,
and control signals to handle cases of video channel underow.
6.5.1 Buffer Reset
Each of the buffers can be reset on an individual basis, i.e., without
affecting the other buffers. Resetting a buffer returns its read and write
pointers to the buffer start address. A buffer is reset when the host sets
the corresponding bit in Register 68 (
page 4-23). When bit 0 in the
register is set, all dened buffers are reset when a packet sync error is
detected.
The Channel Buffer Controller provides a compare function for extracting
actual Decode Time Stamp (DTS) values, i.e., the actual time when a
picture or audio frame starts decoding. The host registers associated
When the Enable Video Read Compare DTS bit is set, the value in the
Video ES Channel Buffer Compare DTS Address registers is constantly
compared with the current value of the video channel read pointer. As
soon as a match is detected, a signal is generated that triggers a state
machine. When the state machine detects a Picture Start Code, the
INTRn output to the host is asserted, if not masked, and the DTS Video
Event Interrupt bit in Register 2 (
page 4-7) is set.
In an actual situation, the host, when alerted, would read the packet
header and the start address of a packet payload from the Audio PES
Header/System Channel Buffer and write that address to the Video ES
Channel Buffer Compare DTS registers. At the rst Picture Start Code
Table 6.16 Compare DTS Register Bits and Fields
Function
Registers
Page Ref.
Enable Video Read Compare DTS
69
Enable Audio Read Compare DTS
69
Video ES Channel Buffer Compare DTS Address
108–110
Audio ES Channel Buffer Compare DTS Address
111–113