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Re: [Freeipmi-devel] KCS Driver & SMS_ATN Register

From: Anand Babu Periasamy
Subject: Re: [Freeipmi-devel] KCS Driver & SMS_ATN Register
Date: Thu, 18 Feb 2010 03:30:39 -0800
User-agent: Mozilla-Thunderbird (X11/20091109)

Matt Jerdonek wrote:

The KCS driver appears to not use the SMS_ATN register. This register is useful for BMC-to-BMC communication to know when the remote BMC has responded. Are there any plans to monitor this register in future releases? If not, are the maintainers open to including a patch?


Hi Matt,
If you use SMS_ATN flag, then you should also call "Get Message Flags" and check if "Receive Message Available" flag is set. SMS_ATN flag can also be set for other reasons such as watchdog pre-timeout, event message buffer full and OEM events.

My understanding was to use OBF flag for this purpose.

Check this out: Figure 9-7, KCS Interface BMC to SMS Read Transfer Flow Chart

SMS_ATN seems logical for this purpose given its name, but IPMI Spec uses OBF in its data flow diagram. SMS_ATN and OBF both seems to do the same job, except OBF is simple. When should we check for SMS_ATN over OBF or should we check both always? Even OpenIPMI KCS driver uses OBF and not SMS_ATN flag for reading from registers.

SMS_ATN seems useful for high level polling (watch dog daemon). If all system management interfaces supports this flag, then it is worth exposing generic bmc_check_idle() api.

Your patches are most welcome.

Anand Babu Periasamy
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