
6-52
Channel Interface
after the read pointer for the Audio PES Header/System Channel Buffer
reached the compare address, the host would be alerted to the start of
decoding for that picture. The host would then read the value of the SCR
counter as the DTS.
In the case of audio, the host can select the read pointer for the Audio
Decoder or the S/P DIF Formatter by setting the Enable Audio Read
Compare bits in Register 69 so that synchronization can be maintained
against either one. When the compare produces a match, INTRn is
asserted if not masked and the DTS Audio Event Interrupt bit (
page 4-7)is set.
The Picture Start Code Read Address (Registers 128–130,
page 4-40)and the Audio Sync Code Read Address (Registers 131–133,
page 4-41)can be used in conjunction with the Picture Start Code Detect Interrupt
bit and the Audio Sync Code Detect Interrupt bit (both in Register 1,
6.5.2 Detecting Potential Underow Conditions in the Video Channel
As previously mentioned, the Channel Buffer Controller keeps track of
the number of items (64-bit words) and pictures in the Video ES Channel
Buffer and reports these to the host through a set of registers. The
Channel Buffer Controller can also be congured by the host to alert the
internal microcontroller when the Video ES Channel Buffer does not
contain enough unread data to construct an entire picture.
To enable this feature, the host writes a numitems/pics threshold value
in Registers 134–136 (see
Table 6.17) and sets the Video Numitems/
Pics Panic Mode Select bits to alert the microcontroller when either the
number of items or pictures falls below the threshold. The microcontroller
then takes suitable action, which may include suspending reconstruction
in order for the video channel to build up. The display is frozen (eld
freeze) on the previously reconstructed picture during the period that
reconstruction is suspended.