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CHAPTER 4 ATM CELL PROCESSOR
Preliminary User’s Manual S14767EJ1V0UM00
331
Table 4-5. Error Reporting Priorities
Underflow
MAX error
CRC error
Length
T1 error
Underflow
-
Underflow
Underflow
Underflow
Underflow
MAX error
-
-
MAX error
MAX error
MAX error
CRC error
-
-
-
CRC error
CRC error
Length
-
-
-
-
Length
T1 error
-
-
-
-
-
4.8.4 Mailbox
ATM Cell Processor uses mailboxes as ring buffers in SDRAM. The structure of a mailbox and the defined
addresses are as follows.
Mailbox start address (A_MSA[3:0])
Mailbox bottom address (A_MBA[3:0])
Mailbox write address (A_MWA[3:0])
Mailbox tail address (A_MTA[3:0])
:The start address of the mailbox
:The bottom address of the mailbox (address following the last address)
:The write pointer
:The tail address that has been read by the host and which is to be updated
Figure 4-45. Mailbox Structure
A_MSA[3:0]
A_MWA[3:0]
A_MTA[3:0]
A_MBA[3:0]
Upon writing an indication, increments the write pointer (A_MWA[3:0]), sets the MM bit for the corresponding
mailbox in the A_GSR register, and issues an interrupt if it is not masked. When updating the write pointer
(A_MWA[3:0]), ATM Cell Processor causes A_MWA[3:0] to jump to the start address (A_MSA[3:0]) if A_MWA[3:0]
has reached the bottom address (A_MBA[3:0]). To read an indication, V
R
4120A RISC Processor uses the read
pointer (A_MTA[3:0]). A_MTA[3:0] is managed by the host: Each time V
R
4120A RISC Processor reads an indication
from the mailbox, it writes the address of the next indication to the read pointer (A_MTA[3:0]). If the write pointer
(A_MWA[3:0]) points to the same address as that pointed to by the read pointer (A_MTA[3:0]), sets the MF bit of the
A_GSR register that corresponds to the mailbox to indicate that the mailbox is full (the MF state), and issues an
interrupt if it is not masked. Once the mailbox enters the MF state, ATM Cell Processor does not execute any
commands.