System Management Bus (SMBus) Specification, version 2.
System Management Bus (SMBus) Specification, version 2.
System Management Bus (SMBus) Specification, version 2.
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<strong>System</strong> <strong>Management</strong> <strong>Bus</strong> (SM<strong>Bus</strong>) <strong>Specification</strong> Version <strong>2.</strong>0<br />
5.6.3.9. Implementation notes<br />
An SM<strong>Bus</strong> ARP Master in a Hot Plug <strong>System</strong> will typically not require the host notify command as it gets<br />
asynchronous indication of a device added or removed via other means, though there’s no restriction in this<br />
specification against using this notification in those types of applications.<br />
A mobile system that has addition and removal of devices on the SM<strong>Bus</strong> can benefit from this command if<br />
the SM<strong>Bus</strong> ARP Master and the removable devices support this command. (Note, there could be one<br />
device in the system that performs the notify on behalf of other devices. <strong>System</strong> software must always run<br />
the FULL ARP process.)<br />
5.6.3.10. ARP execution<br />
The ARP Master must always execute the ARP when it enters the working state and anytime it receives an<br />
SM<strong>Bus</strong> status change indication (device added or removed – e.g. hot plug). The process begins with the<br />
ARP Master issuing the “Prepare To ARP” command. In all cases the ARP Master must be able to resolve<br />
addresses when it receives the “Notify ARP Master” command.<br />
If the possibility exists that SM<strong>Bus</strong> devices may join the system without a corresponding system reset (for<br />
example in hot-plug-capable systems), the ARP Master may optionally choose to issue the Get UDID<br />
(General) command at least once every 10 seconds in order to discover newly added devices that require<br />
address resolution but that don’t support the “Notify ARP Master” command. No device whose AR flag is<br />
clear will respond to this command. However, a newly added device will enter the system with a power-on<br />
reset, which will reset its AR flag. It will respond to a Get UDID (General) command with its UDID. The<br />
host may choose to assign such a newly added device a non-conflicting address or it may choose to re-ARP<br />
the entire bus.<br />
The ARP Master or any other SM<strong>Bus</strong> master can perform device “discovery” or “enumeration” by<br />
executing a subset of the ARP. This is accomplished by issuing the “Prepare To ARP” command followed<br />
by repeatedly issuing the general “Get UDID” and “Assign Address” commands until no device<br />
acknowledges. Until the ARP process is complete the ARP Master must not wait more than two seconds<br />
before issuing a general “Get UDID” command after issuing the previous general “Get UDID” command.<br />
This restriction is important to allow another SM<strong>Bus</strong> master to determine when it is safe to do an<br />
enumeration of the bus.<br />
SBS Implementers Forum 44
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