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CHAPTER 5 SAR FUNCTION
203
5.6 TRANSMIT/RECEIVE INDICATION
The
μ
PD98405 sends an indication to the host as a status indicating the completion of
transmission/reception for each packet. The transmit/receive indication is issued at the following timing.
Transmit indication:
Once all the data in one transmit packet has been read
When a Deactivate_Channel command has been received during packet
transmission and command processing has been completed
Receive indication:
Once all the data in one receive packet has been transferred to system memory
When the reception of a packet has been stopped due to an error
When the Deactivate_Channel command has been received and command
processing has been completed
Early indication based on the early receive interrupt function
The indication is stored to one of the four mailboxes managed by system memory. Two of the mailboxes are
used for storing transmit indication, while the other two are used for storing receive indication. Which of the two
mailboxes is to be used can be selected by the user for each VC.
Transmit indication: Mailbox 2 or 3, set to packet descriptor
Receive indication: Mailbox 0 or 1, set to VC table
When the
μ
PD98405 stores the indication to the mailbox, it sets the corresponding MM bit of the GSR
register to "1", and generates an interrupt if the corresponding bit of interrupt mask register IMR is enabled.
Bit 31 of the transmit indication and bit 15 of Word 3 of the receive indication stored by the
μ
PD98405 must
be always set to "1." The host uses this bit of an indication as a flag to indicate whether the indication in the
mailbox "has been processed," by resetting this bit to "0" after reading the indication. By using this bit as a flag,
two or more indications can be processed at one time by continuing the processing for as long as a "1"
indication is followed by another (this flag does not always have to be changed).
The receive indication stores information relating to the batch and free buffer to which a packet has been
stored. The host processes the receive data (such as padding and removing the AAL-5 trailer) based on the
indication, then transfers the data to an application that is higher in the hierarchy. Then, the host releases the
batch and free buffer it has used to system memory, or adds them to the chain as a new batch and free buffer
for recycling.
The format of the transmit/receive indication is explained below.