Version: 1.18
PRELIMINARY/CONFIDENTIAL
TrueSpeech® Co-Processor
20. The CT8022 is now in playback mode. The CT8022 will consume a compressed speech frame every 30ms.
The following sequence is used by the Host ISR to transfer each compressed speech data frame from the Host to
the CT8022:
a. Host gets interrupt from CT8022 (optionally checks that TX Ready is set).
b. Host writes 10 words (for TrueSpeech 5.3) into the Host Transmit Data Buffer Access Port.
The CT8022 can buffer up to 20 TrueSpeech 5.3 speech data frames ( 600ms ). At the start of playback, the CT8022
will keep re-asserting the TX Ready condition until the internal playback buffer is full, and the CT8022 has
pre-fetched 20 frames. If the Host needs to reduce the number of speech data frames pre-fetched by the CT8022, it
can do so using the playback Set Buffer Depth command (528XH). This can be set to reduce the effective size of the
internal buffer.
Terminating playback:
1. Host disables interrupts from the CT8022 by writing 0000H to the Hardware Control Register.
2. Host writes IDLE = 0000H command or STOP PLAYBACK = 5220H command to the Software Control
Register.
3. CT8022 terminates playback, discards data in its internal playback buffer and clears TX Ready if set (in
Hardware Status Register).
4. CT8022 writes status response to Software Status Register.
5. Host waits for STATUS READY indication in the Hardware Status Register, then reads the CT8022 response
from the Software Status Register. This clears the STATUS READY bit.
When either the Idle or Stop Playback command is used to terminate playback, the CT8022 will discard data in its
internal playback buffer. In some cases, this may not be desired. For example, when playing back TrueSpeech 6.3
data stored in a disk file, if either the Idle or Stop Playback command is issued immediately at end-of-file (EOF), the
last 20 frames (600ms) of the message will not be played. The Host may wish to use the playback Buffer
Monitoring command (5212H). With command, the Host can poll the CT8022 and wait until all the internally
stored speech data has been played out before issuing the Idle or Stop Playback command.
Note: After writing the Idle or Stop Playback command to terminate playback, the Host should not attempt
to access the Host Transmit Data Buffer Access Port even if the TX Ready bit is set.
CT8022A11AQC FW Revision 0118 DSP GROUP, INC., 3120 SCOTT BOULEVARD
SANTA CLARA, CA 95054 PH: 408 986 – 4300 FAX: 408 986 – 4490
75
All specifications are subject to change without prior notice.
ETC [ ETC ]
