Re: how mass storage device cope with unsupported commands?

[Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>]

On Thu, 29 Jun 2006, JackRain wrote:

> 		  the procedure is :
>           1)bulk-out endpoint occurs,read endpoint fifo to get CBW
> 		  2)decode CBW and found the unsupported command
> 		  3)how to react if the command I don't want to implement  ?
>           4)I tried as i told previously but got bus reset.
>   	
>           I want to know the right way:) 

> 		  Shall the endpoint muct be stalled?? 

There are two ways to report that you don't support a command.

The first way:

	If dCBWDataTransferLength > 0 and the Direction bit in
	bmCBWFlags is 0 (Out), stall the bulk-out endpoint.  If
	either of those conditions is false, stall the bulk-in
	endpoint.

	After the host clears the endpoint's halt feature, prepare
	to send a CSW with bCSWStatus = 1 and dCSWResidue = the
	value of dCBWDataTransferLength.

	If the next CBWCB from the host is a REQUEST SENSE command,
	send back key=0x05, ASC=0x24, ASCQ=0x00.

The second way:

	If dCBWDataTransferLength > 0 and the Direction bit in
	bmCWFlags is 0 (Out), receive dCBWDataTransferLength bytes
	on the bulk-out endpoint and ignore their values.  If
	dCBWDataTransferLength > 0 and the Direction bit in bmCBWFlags
	is 1 (In), transmit dCBWDataTransferLength bytes containing
	0x00 on the bulk-in endpoint.  If dCBWDataTransferLength = 0,
	go directly to the next step.

	Send a CSW with bCSWStatus = 1 and dCSWResidue = the value
	of dCBWDataTransferLength.

	If the next CBWCB from the host is a REQUEST SENSE command,
	send back key=0x05, ASC=0x24, ASCQ=0x00.

I don't know if Windows will work properly with the second way.

Alan Stern


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