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We now have two different Harlan A quotes: the 12/13 original, and the 12/17 restatement. I'm ok with the restatement. In the original, I was choking over the idea that a device, same as a host, should be required to keep all the data of a command buffered until the result of the command crosses the bus. I agree buffering all the data is a reasonable requirement to place on desktop hosts ... though I can imagine embedded host folks complaining. > ... If we now agree devices often do move some data in/out before deciding if the total that will move matches the max that the device's interpretation of the command block permits, ... ... perhaps we can agree that with UDma we will see more data move than we did with Pio? Pat LaVarre >>> Harlan Andrews <[EMAIL PROTECTED]> 12/17/01 01:11PM >>> Pat, This was meant EXACTLY as quoted. NO data is valid until the transfer is completed and the data is checked checked. Intermediate data should not be used. In case of error, the ENTIRE transfer should be retried. On read, if the host can't handle ALL the data, it should not request that much. A host should never request more data than it's buffer can receive. If an error happens during write, it is the host's resposibility to retry THE ENTIRE TRANSFER. ...Harlan On 12/17/01, Pat LaVarre <[EMAIL PROTECTED]> said: >This message is from the T13 list server. > > >> Harlan Andrews <[EMAIL PROTECTED]> 12/13/01 05:31PM >> ... >> Neither the device nor the host should use >> ANY intermediate data >> until the transfer is COMPLETED >> and errors are checked. >> Therefore, the "extra" bytes should be completely transparent. > >Hang on a minute, this can't be meant as quoted out of context here? > >An x0A/2A/AA Write block command that fails renders all the content >of the blocks it addresses indeterminate? Maybe commonly only the >blocks before the bad block changed, but only a BadHost assumes >that limited effect? > >Ditto a ModeSelect command: a bad page in the stream doesn't guarantee >that good pages in the stream will have no effect? > >Ditto a WriteBuffer command: a bad Crc for the last burst of bytes doesn't >guarantee the good bytes sent earlier will have no effect? > >Ditto .... > >> Neither the device nor the host should use >> ANY intermediate data >> until the transfer is COMPLETED >> and errors are checked. > >A device can avoid using intermediate data only by buffering all the data >of the command. > >For a command block that moves, say, xFFFF blocks i.e. about 32MiB at >0.5KiB/block, ... no device that buffers less than 32MiB can avoid using >intermediate data. > >Pat LaVarre Subscribe/Unsubscribe instructions can be found at www.t13.org.
