This message is from the T13 list server.
On Sun, 10 Aug 2003 09:03:59 -0700, Mukesh Kataria wrote: >This message is from the T13 list server. >I have a question about DRDY. >BACKGROUND >For PIO IN commands, say IDENTIFY DEVICE, the prerequisite is >that DRDY is set to 1. Similarly after successful command >completion, condition is that "DRDY shall be SET to 1". Most commands to an ATA device require DRDY=1 otherwise the device *may* reject the command (some devices can execute some commands when DRDY=0, of course these devices may not conform to a strict interpretation of the standard).. >QUESTION >What is supposed to happen to DRDY in between. After IDENTIFY >DEVICE command has been sent to device: Not specified what happens DRDY *during* the execution of a command. DRDY never appears in the command execution state diagrams (certainly never appears at a decision point in the host side state diagrams). >- Is device supposed to leave DRDY unchanged (i.e. 1) Doesn't matter but a device that toggles DRDY on/off is definitely not following the traditions and spirit of ATA. Note that there are well defined times when an ATAPI devices turns DRDY on/off, but even with ATAPI it does not matter what DRDY does *during* the execution of a command. >- OR is device supposed to clear DRDY till whole identify packet >has been read thru data port? No, not required and a device that did toggle DRDY would be a strange device. >In all true ATA devices, I see DRDY set during packet reading. >But I have this "emulated" ATA device which clears the DRDY >during PIO in phase and manufacturer says that spec asks device >to set DRDY only "when the device is capable of accepting all >commands" and during packet read (PIO IN) phase device is not >capable of accepting any other command. Ahhh... They are "wrong". I would not call their device "broken" but it sure is "strange". But a host should not care what a device is doing with DRDY *during* the execution a command. There is no reason for the host to be looking at DRDY *during* the execution of a command. Hale *** Hale Landis *** www.ata-atapi.com ***
