How to Exchange SDTR?

Tom Mortensen tomm at maxstrat.com
Wed Jun 4 08:33:58 PDT 1997


* From the SCSI Reflector (scsi at symbios.com), posted by:
* Tom Mortensen <tomm at maxstrat.com>
*
The best way to handle synchronous/wide data transfer
negotiation is to execute this exchange with EVERY
Request Sense command as follows:

        Selection (with ATN)
        Message Out (WDTR)
	Message In (recieved WDTR from target)
        Assert ATN again
        Message Out (SDTR)
	Message In (received SDTR from target)
        Command (Request Sense)
        Data In (sense data)
        Status (command complete)

In this scheme, the Initiator forces two Message Out phases
before the Command phase; the first to set the bus width, the
second to set the clock period/offset.  Note that they must be
in this order since the WDTR will set the clock back to asynchronous.

By doing this with every Request Sense, you can simplify the host
driver.

chunyi wu wrote:
> 
> * From the SCSI Reflector (scsi at symbios.com), posted by:
> * chunyi wu <cperi at public.hz.zj.cn>
> *
> Dear Sir/Ms:
>         I take the liberaty to ask you question about the SYNCHRONOUS DATA
> TRANSFER REQUEST(SDTR) message exchange as Initiator. The procedures I
> did are:
>  1.Selection Phase(with ATN)
>  2.Message Out Phase.(sent the Identity Message, and 5 bytes SDTR)
>  3.Message In Phase. (received the SDTR from Target)
>  4.Command Phase??
>  5.
>         In the step4, the system always goes Command Phase. Is this the case
> under the ISO/IEC 9316? I do not know how to end the SDTR message
> exchange normally. Do I have to issure some SCSI command in the step
> 4(Command Phase) to successfully quit the SDTR exchange? Is there any
> other way to do so??
>         I am looking forward to your reply!
> Thanks and Have a good day.
> --
> Chunyi Wu
> Senior Engineer,Project Magr
> Hangzhou Computer Peripheral Equipment Research Institute
> Email      :  cperi at public.hz.zj.cn
> *
> * For SCSI Reflector information, send a message with
> * 'info scsi' (no quotes) in the message body to majordomo at symbios.com

-- 
Tom Mortensen                   mailto:tomm at maxstrat.com
MAXSTRAT Corporation            http://www.maxstrat.com/
801 Buckeye Court               Tel:408/383-1600
Milpitas, CA  95035-7408        Fax:408/383-1616

*
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