Alert Standard Format (ASF) Specification

Alert Standard Format (ASF) Specification v2.0 DMTF Document DSP0136
DSP0136 23 April 2003 Page 52 of 94
1. to ensure that an alert sending device does not dominate the SMBus
2. to ensure that every sensor in the system is polled within a reasonable time.
To achieve these goals the Minimum Inter-poll Wait Time specifies the amount of time, in 5
millisecond units, an alert-sending device must wait between the completion of one event-polling
cycle to the start of the next. If the device uses the SMBus Get Event Status message to start its
polling cycle, the cycle includes any Get Event Data messages necessary to retrieve event-
specific data. If the device uses only SMBus Get Event Data messages, each cycle is limited to a
single message. The following diagram illustrates these two conditions.
Get
Event
Data
Get
Event
Data
Get
Event
Data
Get
Event
Data
ASF Sensor
Inter
-
p
oll
Time
ASF Sensor
Inter
-
p
oll
Time
ASF Sensor
Inter
-
p
oll
Time
Time
Polling with the
Get Event Data
Message for ASF Sensors
System implementers should set this time so that no one alert-sending device uses more the 25%
of the SMBus bandwidth for the Poll Alert Message
s, and so that each sensor is polled at least
once a second. Following are guidelines for choosing this system-specific value:
• If all the sensors can run at 100KHz without doing any SMBus clock stretching, then the alert-
sending device’s poll with alert data for a single sensor will take about 1.2 milliseconds. If the
wait time is 10 milliseconds (a field value of 2), then the alert-sending device will use less
than 25% of the SMBus bandwidth (about 12%) and 83 sensors can be polled in one (1)
second.
• If, on the other hand, the sensors run at the slowest SMBus speed (10KHz) an alert-sending
device will require about 12 milliseconds to poll a single sensor. The wait time should be set
to 35 milliseconds (a field value of 7) to keep the bandwidth below 25%. This still allows 21
sensors to be polled in one (1) second.
Get
Event
Status
ASF Sensor
Inter
-
p
oll
Time
ASF Sensor
Inter
-
p
oll
Time
ASF Sensor
Inter
-
p
oll
Time
Time
Polling with the
Get Event Status
Message for ASF Sensors
*
The Get Event Status message identifies the status change(s) and the Get Event Data message corresponds to the data associated with the specific status
change(s)
Get
Event
Status
Get
Event
Status
Get
Event
Status
Get
Event
Data
Get
Event
Data