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CHAPTER 5 SAR FUNCTION
168
5.5 RECEPTION FUNCTION
5.5.1 Reception Processing Flow
The reception of cells by the
μ
PD98405 is divided into several stages as illustrated below.
Figure 5-30. Outline of Reception Flow
Host processing
μ
PD98405 operation(for AAL-5 packet reception)
(1) Sets VRR register
(7)
Receives first cell of packet
(2) Sets receive pool in system memory
(8)
Assigns batch of pool
(3) Sets receive pool descriptor in control memory
(9)
Links VC to T1 timer list (monitors T1 error)
(4) Open_Channel command
(10) Transfers data to system memory in segment units
(5) Sets receive VC table
(11) Assigns new batch if necessary
(6) Sets lookup table entry in control memory
(12) Receives last cell of packet
(13) Checks error from AAL-5 trailer
(15) Reads receive indication
(14) Issues receive indication and interrupt
(16) Updates mailbox read pointer (MTA)
(17) Reads data from receive pool
(18) Manages buffer of receive pool
(Add_Batches command)
μ
PD98405 operation (for raw cell reception)
(7)* Receives a cell
(8)* Checks CRC-10
(9)* Transfers data to system memory as raw cell data
(10)* Sets RCR bit of GSR register then issues interrupt
The
μ
PD98405 supports 32K VCs (any combination of receive VCs and transmit VCs). The number of
receive VCs actually supported is determined by setting the bits of the VPI/VCI field.
(1)
The
μ
PD98405 supports up to 16 bits of the 24 bits of a receive VPI/VCI. The user determines the
method to be used to convert the 24 bits of the VPI/VCI to be received into a 16-bit logic code, and
sets this method in the VRR register.
(2)
Before reception, a receive pool that stores receive data is prepared in system memory.
(3)
Information such as the receive pool size of the system memory and address is set in the free buffer
pool pointer area of the control memory as a pool descriptor.
(4)
The host issues an Open_Channel command for each connection to be received to open a channel
(VC). The
μ
PD98405 allocates a block to be used as the VC table from the free block pool of control
memory and returns the address of that block to the host.
(5)
The host initializes the parameters of the VC table.
(6)
Next, the host sets the address of the VC table in the lookup table to actually start reception, and
enables reception.