Freescale Semiconductor MPC8260 - Manual (Page 1037)

ATM AAL1 Circuit Emulation Service
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
Freescale Semiconductor 31-21
Figure 31-19. 3-Step-SN-Algorithm
31.7 Pointer Verification Mechanism
After the 3-step-SN algorithm processes the incoming cells, the cells status (Valid, Tag, Drop or Dummy)
is delivered to the pointer verification mechanism. This state machine calculates the expected received
pointer. If the current cell is valid and supposed to deliver a pointer, the received pointer is compared with
the expected one. In the case of pointer mismatch or pointer error (i.e parity error), the pointer state
machine switches to “Pre-Hunt-Mode”. If the cell status is not valid (i.e Tag, Drop or Dummy) and it
supposed to carry a pointer, the pointer declared a mismatch and the pointer state machine switches to
“Pre-Hunt-Mode”. The receiver stays in this transient state for only one AAL1 cell cycle (8 successive
cells). When the pointer received in this state is different from the expected one or had a non-valid status,
the receiver switches to hunt mode where it stays until a valid cell with a “start” structured pointer is
received to regain synchronization.
Note that a “start” pointer is a valid pointer with a value not equal to 93 or 127.
Hunt mode
Sync fail
Sync mode
No valid SN
Else
Valid SN
Valid SN
Invalid SN or
out of sequence
Valid SN
ESC=RSC–1/0/1