MT92220 Zarlink Semiconductor, MT92220 Datasheet - Page 146

• Manufacturer Part Number: MT92220
• Description: 1023 Channel Voice Over IP/AAL2 Processor
• Manufacturer: Zarlink Semiconductor

146
10.3
The RX TDM module is responsible for copying data from the circular buffers contained in SSRAM B and passing
them on to the H.110 interface. The RX TDM uses an RX Channel Association Memory to associate each of the
1023 time slots it supports to either a PCM buffer or an HDLC stream. The chip can support up to 1023 PCM buffers
or up to 512 HDLC streams, or any combination of the two (two PCM buffers cost the same as 1 HDLC stream).
Any of the 1023 time slots supported can also be configured as Low Latency Loopback: this means that the data
sent onto the time slot will not come from a circular buffer but will be received from another time slot on the bus,
treated by the TX TDM.
This is the format of the RX Channel Association Memory:
Stream/Buffer Tag
AS
TSST
Link to next entry
RX T\DM Data Path
Field
+0
+2
+4
+6
RX Channel Association Memory Entry
b 15
AS
Encoded field that points either to the RX TDM Control memory (for xxPCM Buffer
and HDLC stream) or to the Low-Latency Loopback Memory for Low-Latency
Loopback channels.
Associated Stream. When set, the least significant bit of the TSST number will be
ignored and both even and odd streams pointed to by the TSST number will be
driven out with valid data. For xxPCM circular buffers, the extra stream allows PCM
/ ADPCM codec changes to occur smoothly. For HDLC streams, the extra stream
doubles the bandwidth that is available on the HDLC stream.
Time / Stream Number. TSST[11:5] represents the timeslot on which the data
belonging to an HDLC stream or to an xxPCM buffer will be sent on. TSST[4:0]
represents the stream on which the data belonging to an HDLC stream or to an
xxPCM buffer will be sent on.
Pointer to the next RX Channel Association Memory Entry. Entries must be sorted
according to TSST number (incrementally). Entry 0 is never considered to contain a
Buffet Tag; it’s TSST is hardcoded in the chip as number -1, which means that the
last RX Channel Association Memory Entry must point back to Entry 0 to be ready
for the next frame.
b14
Figure 81 - RX Channel Association Memory
b13
91FF0h
91FF8h
90000h
90008h
b12
Table 61 - Fields and Description
b11
b10
Zarlink Semiconductor Inc.
b9
b8
Entry 1022
Entry 1023
Entry 0
Entry 1
b7
TSST [11:0]
Stream/Buffer Tag
b6
Link to next entry
b5
Description
b4
b3
b2
b1
b0
: