MT90500 Datasheet, PDF (33/159 Pages) Mitel Networks Corporation – Multi-Channel ATM AAL1 SAR

MT90500
4.1.2.5 Local Bus Data Transfer Process
A local bus data transfer process is provided, which allows local serial TDM input (LOCSTi) data to be output
on the main TDM bus (ST[15:0]) in place of the usual data from the internal frame memory. Similarly, data from
the main TDM bus can be routed directly onto the local TDM output (LOCSTo), without affecting the TDM to
internal frame memory transfer.
The local bus pins on the MT90500 are an extension of the main TDM bus. The data on any stream of the main
TDM bus may be passed to the local bus output (LOCSTo). The source pin (one of ST[15:0]) is controlled with
the STi2LOCSTo bits at 6020h, and the time slots to be transferred are indicated by the TDM Bus to Local Bus
Transfer Register (6022h). Note that this TDM data can be from two sources: either externally-sourced data
being driven into the selected ST pin, or data from the ATM link being driven out by the RX_SAR, and copied to
the LOCSTo pin. When fewer than the maximum number of available time slots are transferred between the
main TDM bus and the local bus, the unused LOCSTo output time slots are filled with data fed back internally
from LOCSTi.
Similarly, the data input on LOCSTi may be passed to any stream of the TDM bus as indicated by the Local Bus
to TDM Bus Transfer Register (6024h), and the LOCSTi2STo bits at 6020h. Note that when the local bus to
TDM process is enabled, from 1 to 32 data bytes from the RX_SAR will be replaced by local bus data. The
enable bits for the main TDM bus channels are the normal bits in the Output Enable Registers (7000h + 2N).
Data from the LOCSTi input pin can be transferred to the ATM link through the TX_SAR, by re-sampling the
channels on which the local bus data is output as inputs to the TX_SAR.
4.1.3 TDM Data to External Memory Process
4.1.3.1 General
The segmentation of serial TDM input data into ATM cells starts by copying the TDM data into Transmit Circular
Buffers. The data is then read out of the Transmit Circular Buffers by the TX_SAR (see Section 4.3.2, “TX_SAR
Process,” on page 48). The initial step of copying the serial TDM input data into the Transmit Circular Buffers is
performed by the TDM Data to External Memory Process described in this section.
TDM Buses
Internal Memory
TDM Input
Frame Buffer
External Memory
TXCBBASE (Register 6044h)
Tx Circular Buffer 1
TXCBBASE+64
Tx Circular Buffer 2
TXCBBASE+128
Tx Circular Buffer 3
Tx Circular Buffer n-1
Each active DS0
channel occupies a
64-byte Transmit
Circular Buffer.
Tx Circular Buffer n
Figure 4 - TDM Frame Buffer to External Memory Transfer
All of the serial TDM input data available on the TDM buses is first written to an internal frame buffer which
holds 4 frames of TDM data per input channel. As shown in Figure 4, this internal frame memory (which is used
in both the receive and transmit directions simultaneously) is used as a pingpong buffer. While one page of the
memory is being loaded with input TDM data, the other page of the memory is being transferred to the Transmit
Circular Buffers in external memory. This transfer occurs every 500 µs (4 frames * 125 µs per frame).
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