Date: Fri, 2 Oct 1998 15:58:55 -0600 (MDT) From: "Justin T. Gibbs" <gibbs@narnia.plutotech.com> To: "FreeBSD SCSI Users' list" <freebsd-scsi@FreeBSD.ORG> Cc: scsi@FreeBSD.ORG Subject: Re: ahc & CAM: strange diagnostic Message-ID: <199810022158.PAA12488@narnia.plutotech.com> In-Reply-To: <19980929082453.A328@nagual.pp.ru> <xzp90j31010.fsf@yggdrasil.ifi.uio.no> <19980930011432.B15508@keltia.freenix.fr> <19980930154002.A14288@matti.ee> <19980930235134.B24498@keltia.freenix.fr> <19981002153211.A13506@matti.ee> <19981002220353.A17421@keltia.freenix.fr>
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>> ncr0: <ncr 53c875 fast20 wide scsi> rev 0x03 int a irq 9 on pci0.9.0 >> da0 at ncr0 bus 0 target 5 lun 0 >> da0: <QUANTUM VIKING II 4.5WSE 5520> Fixed Direct Access SCSI2 device >> da0: 40.0MB/s transfers (20.0MHz, offset 16, 16bit), Tagged Queueing Enabled >> da0: 4350MB (8910423 512 byte sectors: 255H 63S/T 554C) > > Funny. My IBM drives report an offset of 15 with the ASUS and my new > VikingII reports 8 on the built-in 7880 UW board... The aic7880 can only handle a sync offset of 15 bytes in narrow mode and 8 bytes in wide mode. This is a restriction of the chip, not the drive. > What is the exact meaning of "offset" ? In synchronous SCSI, the devices of a connection negotiate the clock rate at which data transations occur as well as the size of the sliding data "window" of unacknowledged transactions. The offset is the SCSI term for the window size. So, if a device says it has an offset of 8, it has said that it has buffer space to recieve 8, unacknowledged transactions. This provides some slack for transmission and processing latencies. -- Justin To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the message
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