am79c864a Advanced Micro Devices, am79c864a Datasheet - Page 31

• Manufacturer Part Number: am79c864a
• Description: Physical Layer Controller With Scrambler Plc-s
• Manufacturer: Advanced Micro Devices

Line State Machine (LSM)
In the FDDI network, a special group of symbols called
Line State Symbols (Q – Quiet, H – Halt, I – Idle) are
transmitted to establish the physical connection be-
tween neighboring stations. These Line State Symbols
are unique in that they may be recognized independ-
ently of symbol boundaries.
The LSM constantly monitors symbol pairs coming from
the Elasticity Buffer. The current symbols pair is en-
coded (ENC_CSP) and compared to the encoded value
of the previous symbol pair (ENC_PSP). The symbol
pairs are counted by the Symbol Pair Counter
(SYM_PR_CTR – bits 2–0 in the PLC_STATUS_A
Register) until a Line State is reached. Once a Line
State is reached the SYM_PR_CTR is stopped, the new
line state (LINE_ST – bits 7–5 in the PLC_STATUS_A
Register) is stored and the UNKN_LINE_ST bit is reset
to zero. Upon receiving the first symbol pair that is not
identical to the previous symbol pair (and is not a JK or
noise symbol pair) the SYM_PR_CTR is started and
UNKN_LINE_ST is set to 1 until conditions for the next
Line State are met.
The recognition of these Line States is reported to the
PCM, which uses this information for insertion and
removal of the station from the ring, ring recovery and
maintenance. A change in the value of LINE_ST is re-
ported to the Node Processor by means of an interrupt
which can be enabled or disabled by setting the
MATCH_LS bits in the PLC_CNTRL_B register.
The LSM is reset into the NOT_ACTIVE state with
LINE_ST = NLS, UNKN_LINE_ST = 0, SYM_PR_CTR
= 000 and PREV_LINE_ST = QLS.
The function of the LSM State Machine is described in
Table 11.
Link Error Monitor (LEM)
The Link Error Monitor provides an indication of the in-
bound link quality to the Physical Connection Manage-
ment entity. The PCM uses this information to determine
State
LSM0
LSM1
Description
This is the NOT ACTIVE state. The LSM is
anything other than ALS. A transition to
LSM1 will occur whenever ENC_CSP = JK.
This is the ACTIVE state. The LSM will
stay in this state only if ENC_CSP = JK,
DATA, or II (if ENC_CPS = I I then only if
ENC_PSP not = I I). Anything else will cause
a transition to LSM0.
in this state whenever LINE_ST equals
Table 11. LSM State Descriptions
P R E L I M I N A R Y
Am79C864A
if the Link Confidence Test passes to establish a new
connection. Once a link is active the PCM continually
runs a Link Error Monitor test to detect and isolate links
having an inadequate bit error rate.
The LEM hardware consists of a detector, accumulator
and threshold element. The detector is a state machine
which constantly monitors incoming symbol pairs on the
receive path. When Link Error Events are detected they
are counted by the 8-bit Link Error Event Counter
(LINK_ERR_CTR).
matches the count written to the Link Error Event
Threshold Register (LE_THRESHOLD) the LE_CTR bit
in the INTR_EVENT register is set.
A Link Error Event is defined in Table 12 below. Note
that a number following an H or V symbol indicates the
value of that symbol’s encoding. For instance, H2 is the
symbol “00010”, V5 is the symbol “00101”, etc.
Physical Connection Management (PCM)
Connection Management (CMT) defines the operation
of Physical Layer (PHY) insertion and removal, and the
connection of PHY entities to the Media Access Control
(MAC) entities. Physical Connection Management
(PCM) is a subset of CMT. Fundamental to this task is
the management of a connection between two physical
attachments (PHYs) in adjacent stations. It is the job of
the PCM state machines in both stations to cooperate in
forming a connection between the two PHYs within the
rules established by the Connection Management.
Noise Events
Transition from Idle Line
State to Noise Line State or
Unknown Line State
When in Active Line State,
detection of the symbol pair:
XV’, V”X, J ~K, ~JK, or I D
where:
V’ = H1, H2, H8, H16, V3, V5,
V6, V12, or J
V” = H1, H2, H8, H16, V3, V5,
V6, V12, or K
D = n, R, S, or T
X = don’t care
~K = not K; ~J = not J
When in Active Line State,
detection of the symbol pair:
I I followed by D X
I I followed by I D
Other transitions from Active
Line State to Noise Line State H4 H4 which causes the
or Unknown Line State
Table 12. LEM Error Events
When
Exceptions
When the symbol pair
which causes the transition is
followed by: QQ, QH, HQ, or HH
None
None
When the symbol pair
transition is followed by:
H4 Q, Q H4, I I, H4 I, or JK
the
LINK_ERR_CTR
AMD
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