Date: Wed, 1 Sep 1999 17:55:09 -0600 (MDT) From: "Kenneth D. Merry" <ken@kdm.org> To: remy@synx.com Cc: freebsd-scsi@FreeBSD.ORG Subject: Re: command delay offset Message-ID: <199909012355.RAA03250@panzer.kdm.org> In-Reply-To: <199909012340.BAA07963@gw0.boostworks.com> from Remy Nonnenmacher at "Sep 2, 1999 01:40:49 am"
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Remy Nonnenmacher wrote... > Sorry to bother you with a so simple question, but.... > > what is the 'command delay offset' (aka offset) role ? What values can > be set via camcontrol negotiate -O ? It allows you to specify the SCSI REQ/ACK offset. The REQ/ACK offset is, along with the period/sync rate, part of synchronous data transfer negotiation. Here's a quote from the SCSI-2 spec: "The REQ/ACK offset specifies the maximum number of REQ pulses that can be sent by the target in advance of the number of ACK pulses received from the initiator, establishing a pacing mechanism. If the number of REQ pulses exceeds the number of ACK pulses by the REQ/ACK offset, the target shall not assert the REQ signal until after the leading edge of the next ACK pulse is received. For successful completion of the data phase is that the number of ACK and REQ pulses shall be equal." In networking terms, it's the window size. Keep in mind that 'camcontrol negotiate' is only supported for a few boards, and some support it better than others. In general, if you set the offset to 0, you will end up disabling synchronous negotiation for that device. If you set the offset to a non-zero value, generally the controller will attempt to negotiate the given offset with the device. Ken -- Kenneth Merry ken@kdm.org To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the message
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