Version: 1.18
PRELIMINARY/CONFIDENTIAL
TrueSpeech® Co-Processor
6.2.1.1
CODEC Sync Mode
In CODEC Sync Mode, Host-CODEC synchronization is maintained on a 30ms frame-by-frame basis. The CT8022
does not perform any additional internal buffering. This mode provides minimum delay with the tightest coupling
between CODEC-CT8022 transfers and CT8022-Host transfers (there is a 1-frame delay). In this mode, the Host
must ensure that it is able to perform a data transfer every 30ms. Data transfers are performed by the Host processor
and take place through the Software Control and Status Registers. This mode is compatible with the data transfer
protocol used by the CT8005 TrueSpeech Messaging Co-Processor. In this protocol, the playback/record command
sequence is directly synchronized with the 30ms frame rate by delaying the Status responses until the frame is ready.
This causes the CT8022 Host interface to block or wait on a command to transfer data. This blocking means that
this mode can only support half-duplex data transfers, i.e. concurrent playback/record is not supported in this mode.
While the command/status interface is blocked waiting for the next frame, the CT8022 is unable to process other
commands. The blocking effect also means that only 1 frame can be transferred to the CT8022 each frame period.
Consequently, the effective buffer depth of the CT8022 is 1, regardless of the buffer limit setting. Software designed
to support the CT8005 may depend on the blocking feature in order to use the rate at which the CT8005 responds in
order to measure the progress of time. An additional property of this mode is that a data frame can always be
transferred once the CT8022 has returned a status response (the transfer count returned in the S3 status response is
always non-zero). CODEC Sync Mode is the default mode of the CT8022 following reset.
6.2.1.2
Data Sync Mode
This mode operates in a manner similar to the CODEC Sync Mode, but with additional buffering being provided
within the CT8022. This relaxes the requirement that the Host be able to respond to a transfer request from the
CT8022 every 30ms (depending on the buffer limit set). This mode provides a degree of compatibility with the
CT8005 TrueSpeech Messaging Co-Processor, while also providing additional buffering.
Blocking of the command/status interface can be avoided in this mode by using the buffer depth polling commands
prior to issuing the data transfer (play/record) commands. By checking the buffer depth, the Host can avoid reading
from an empty record buffer, or writing to a full playback buffer.
This mode is selected automatically when the CT8022 enters Host-to-Host (CODEC-less) compression or
decompression mode. This default can be over-ridden by changing the sync mode after the start of Host-to-Host
mode.
6.2.1.3
Poll Sync Mode
In Poll Sync Mode, the CT8022 maintains internal frame buffers that are linked directly to the Host interface
transmit/receive data buffers. Available receive data is transferred automatically to the Host interface receive buffer
unless the buffer is full. Any data placed in the Host interface transmit buffer is automatically transferred to the
internal transmit buffer unless that buffer is full. This mode is recommended for DMA transfers where there is no
frame-by-frame Host supervision (no C2-S2-C3-S3 play/record command sequence is required).
Poll Sync Mode is a non-blocking variant of Data Sync Mode. Regardless of the data transfer option selected, the
command/status responses occur without waiting to synchronize with the 30ms frame period. When the record
buffer is empty or the playback buffer is full, the CT8022 returns zero as the transfer count in the playback/record S3
status response. Data may be transferred via the Software Control and Status Registers, via the transmit and receive
data buffers using the Host processor, or via the transmit and receive data buffers using a DMA controller.
6.2.1.4
Host Sync Mode
Host Sync mode is similar to Poll Sync Mode, except that the Host is always given permission to perform the
transfer it requests, irrespective of the internal transmit and receive state. The CT8022 accommodates this by
creating or discarding data as necessary.
CT8022A11AQC FW Revision 0118 DSP GROUP, INC., 3120 SCOTT BOULEVARD
SANTA CLARA, CA 95054 PH: 408 986 – 4300 FAX: 408 986 – 4490
45
All specifications are subject to change without prior notice.
ETC [ ETC ]
