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CHAPTER 5 SAR FUNCTION
221
Setting the receive VC table
The host sets the receive VC table to its initial values. In addition to the settings for the VBR VC table,
the host must set values specific to the ABR service. The settings specific to the ABR receive VC are
as follows:
<1>
Set the ABR bit to 1 to indicate that the VC uses the ABR service. Also, set the RE bit to 1.
<2>
Set, in the Tx VC TABLE POINTER field of word 7, the VC NUMBER of a transmit VC (VC used
to send back a BRM cell) that is paired with this receive VC.
<3>
Set the ABR parameter obtained through negotiation. (See
Section 5.8.4
.)
(6) Setting the receive lookup table entry
It is necessary to specify the receive lookup tale entry, because the ABR service uses a receive VC
regardless of whether data is being transmitted or received.
At the data receiving end (destination), a receive pool is allocated in system memory. Setting a receive VC
NUMBER in the receive lookup table entry and enabling table entry ready the receiving end for reception
(the receive VC becomes active). The structure and behavior of the receive pool are the same as for the
VBR VC. See
Section 5.5
for details.
No receive pool is required for the ABR service if it is used only at the data transmitting end (source), when
no data cell is received at the turn-around BRM cell receive VC. The
μ
PD98405 does not store RM cells in
the receive pool. It only requires that the receive lookup table entry be set.
(7) Tx_Ready command
When the host issues a Tx_Ready command, it makes the ABR transmit VC active, causing the
μ
PD98405
to begin data transmission. The transmission rate used here is adjusted automatically according to the
behavior of the source. The receive lookup table entry must be enabled before the Tx_Ready command is
issued. The structure of the transmit data is the same as that for the VBR VC. See
Section 5.4
for details.
(8) Processing transmit and receive indications
The
μ
PD98405 posts notification of when data transmission or reception ends, by using an indication.
Processing of the indication and mailbox at the end of data transmission or reception is the same as for the
VBR VC. See
Section 5.6
for details.