Sensoray 2600 - Manual (Page 17)

2600 Family Instruction Manual 12 Chapter 3 : IOM Gateway
• Determines which of the MM’s LNK indicators to
activate.
• Enables the Ethernet client to determine the states of all
IOM ports.
An IOM will activate its LNK indicator upon receipt of any
valid ModCmd. Similarly, the gateway will activate the MM’s
LNK indicator for any IOM port that is a member of the APL.
The APL is implemented as a 16-bit integer value, with one bit
representing each IOM port. When an APL bit is set, the
associated IOM port is active. If an APL bit is cleared, the
associated IOM port is not active.
3.7.3 Link Detection Mechanism
A LinkQuery is a special action that is recognized by all IOMs.
When an IOM receives a LinkQuery it sends a response to let
the MM know that a module is present. Unlike most other
actions, receipt of a LinkQuery will not light an IOM’s XMT
indicator, and transmission of a LinkQuery response will not
light the IOM’s RCV indicator.
By means of LinkQuery actions, the MM periodically queries
IOM ports in order to detect connection changes. These
queries are performed autonomously by the MM; no client
activity is required. Link queries are initiated by the MM only
when no client communications are in progress.
The MM queries all IOM ports, whether or not they are
members of the APL. An IOM port is automatically added to
the APL if a new connection is detected on the port. Similarly,
an IOM port is automatically removed from the APL if its
existing gateway-to-IOM connection is broken.
3.7.4 IOM Port States
The gateway maintains a virtual state machine for each IOM
port. Each IOM port state machine operates independently of
the other gateway ports. A virtual IOM port state machine has
four states, as shown in Figure 15.
Figure 15: IOM Port States
3.7.4.1 Signal Names
The following symbolic names are used in the state diagram to
indicate state machine input signals:
• Rst is synonymous with the target IOMs HRST flag bit,
which is present in all MRsps returned from the IOM.
When active, this signal indicates that the IOM has
executed a soft or hard reset.
• Rsp indicates that an MRsp was received from the target
IOM.
• GWRst indicates that the gateway is executing a soft or
hardware reset.
3.7.4.2 State Descriptions
Reset State. The gateway issues a SoftReset action to the
target IOM and then unconditionally switches to the Sync
state. The SoftReset action is issued even though it is not
known whether an IOM is connected to the port. The Reset
state is always entered in response to a gateway reset,
regardless of the current state. Communications between the
gateway and the connected IOM (if any) are inhibited in the
Reset state.
Sync State. The gateway issues a SetWatchdog action to
the target IOM and then waits for either an MRsp or MRsp
time-out, whichever occurs first. The SetWatchdog action is
issued even though it is not known whether an IOM is
connected to the port. In the case of an MRsp time-out, the
Reset
Init
Sync
GWRst
R
sp
*
R
st
Connect
Rsp * Rst
R
sp
+
R
sp
*
R
st
R
sp
Rsp
Rs
p *
Rs
t
Link
Rsp +
Rsp
* R
st
Active