PEB 20560
Functional Block Description
Semiconductor Group
2-34
2003-08
Arbiter State Machine
The D-channel assignment is performed by the arbiter state machine (ASM),
implementing the following functionality.
(0)
After reset or when SACCO-A clock mode is not 3 the ASM is in the state
“suspended”
. The user can initialize the arbiter and select the appropriate SACCO
clock mode (mode 3).
(1)
When the receiver of SACCO-A is reset and clock mode 3 is selected the ASM
enters the state
“full selection”
. In this state all D-channels enabled in the
D-channel enable registers (DCE) are monitored.
(2)
Upon the detection of the first ‘0’ the ASM enters the state
“expect frame”
. When
simultaneously ‘0’s are detected on different IOM-2 channels, the lowest channels
number is selected. Channel and port address of the related subscriber are latched
in arbiter state register (ASTATE), the receive strobe for SACCO-A is generated
and the DCE-values are latched into a set of slave registers (DCES). Additionally a
suspend counter is loaded with the value stored in register SCV. The counter is
decremented after every received byte (4 IOM-frames).
(3)
When the counter underflows before the state “expect frame” was left, the
corresponding D-channel is considered to produce permanent bit errors (typical
pattern: …111011101011…). The ASM emits an interrupt, disables the receive
strobe and enters the state
“suspended”
again. The user can determine the
affected channel by reading register ASTATE. In order to reactivate the ASM the
user has to reset the SACCO-A receiver.
(4)
When seven consecutive ‘1’s are detected in the state “expect frame” before the
suspend counter underflows the ASM changes to the state
“l(fā)imited selection”
.
The previously detected ‘0’ is considered a single bit error (typical pattern:
…11111101111111111…). The receive strobe is turned off and the DCES-bit
related to the corresponding D-channel is reset, i.e. the subscriber is temporarily
excluded of the priority list.
(5)
When SACCO-A indicates the recognition of a frame (frame indication after
receiving 3 bytes incl. the flag) before the suspend counter underflows the ASM
enters the state
“receive frame”
.
(6)
The ASM-state changes from “receive frame” to
“l(fā)imited selection”
when
SACCO-A indicates “end of frame”. The receive strobe is turned off and the
DCES-bit related to the corresponding D-channel is reset. The ASM again monitors
the D-channels but limited to the group enabled in the slave registers DCES
“anded” with DCE. The “and” function guarantees, that the user controlled disabling
of a subscriber has immediate effect.
(7)
When the ASM detects a ‘0’ on the serial input line it enters the state
“expect
frame”
. Channel and port address of the related subscriber are latched in the
arbiter state register (ASTATE), the receive strobe for SACCO-A is generated and