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CHAPTER 4 ATM CELL PROCESSOR
Preliminary User’s Manual S14767EJ1V0UM00
325
4.8.3 Receiving function
Receiving data structure is described in Section. 4.5.2.
4.8.3.1 Receiving procedure
(a) Setting up a receive pool
Before receiving a packet, V
R
4120A RISC Processor prepares the receive pool used to store receive data and
sets the information about the pool in the pool descriptor in Work.
(b) Opening the receive channel
If V
R
4120A RISC Processor is going to open a new connection, V
R
4120A RISC Processor issues
Open_Channel command. If Open_Channel command is issued, ATM Cell Processor assigns VC Table from
VC Table pool in Work RAM and reports its start address to V
R
4120A RISC Processor using a command
indication. V
R
4120A RISC Processor sets the assigned block as a VC table.
(c) Setting the receive VC table
V
R
4120A RISC Processor sets the 16-word blocks assigned from VC Table pool in Work RAM as the receive
VC table for each VC.
(d) Setting up the reception lookup table
The VPI/VCI of the receive cell are set in the receive lookup table.
(e) Receiving the first cell of the packet
Upon ATM Cell Processor receiving a cell, it checks if the VPI/VCI of the received cell has been registered in
receive lookup table. If not registered, the cell is discarded. If registered, ATM Cell Processor gets the VC
number from receive lookup table. If it is a first cell of a packet, ATM Cell Processor assigns the new buffer
directory. The VC is added to the T1 timer list.
(f) Receiving a cell
ATM Cell Processor transfers the segment data from SAR FIFO to SDRAM using Scatter/Gather DMA. In the
same way as in transmission, the CRC-32 value calculated for each segment is stored into the "CRC-32" field
of the VC table. The "Current Count of Segments and "Remaining words in current buffer" fields in the VC table
are updated.
(g) Receiving the last cell
<1> The trailer information is checked for errors.
<2> A receive indication is stored into the mailbox and reported with an interrupt.
(h) Reading the receive indication
V
R
4120A RISC Processor reads the receive indication, updates the read pointer in the mailbox, and extract
receive data from the pool.