MT90500 Mitel Semiconductor, MT90500 Datasheet - Page 67

• Manufacturer Part Number: MT90500
• Description: Multi-Channel ATM AAL1 SAR
• Manufacturer: Mitel Semiconductor

4.5.4
As mentioned above, the MT90500 is capable of receiving non-CBR data cells as well as CBR cells. Non-CBR
cells can be received on the UTOPIA bus and written into the user-defined Receive Data Cell FIFO in external
memory, where they wait for the CPU to read them.
There are 3 ways for cells to be identified as data cells. First of all, OAM cells may be treated as non-CBR cells
if the OAM Routing Select bit in the UTOPIA Control Register (address 4000h, bit<5>) is set to 1. Secondly,
unknown cells may be considered as non-CBR cells if the Unknown Routing Select bit (bit<6> of the UTOPIA
Control Register) is set to 1. Finally, normal cells whose VPI and VCI values correspond to those in the VPI and
VCI Match Registers located at 4012h and 4016h respectively, can be tagged as data if their entry in the look-
up table is associated with a non-CBR entry.
To write into the Receive Data Cell FIFO, the chip will use the Receive Data Cell FIFO Base Address Register
(address 4020h) and will write into the next available entry as tagged by the Receive Data Cell FIFO Write
Pointer Register (address 4022h), regardless of the value in the RX Structure Address field of the look-up table
entry. Once this is done, the write pointer will be incremented.
Finally, the CPU should read the data contained in the FIFO once the write pointer becomes greater than the
read pointer. To do so, the CPU should access each of the 24 word entries corresponding to that cell (24 words
* 2 bytes = 48 bytes, max. cell payload). Once it has completed its task, the read pointer should be incremented
to ensure the hardware knows the cell has been read.
(LUTBASE + “00000”) + VPVCC
Non-CBR Data Cell Reception Ability
31
T = “01” indicates a non-CBR data cell
RX Structure Address (can be ignored)
Figure 28 - Look-up Table Non-CBR Data Entry
T = Entry Type (refer to Figure 27, “MT90500 Cell Receive Process,” on
page 66 for details for non-data cells)
R = Reserved (should be set to all zeroes)
18
01
16 15
R
2
R R
MT90500
0
67