Re: Question about standby timer & standby command.

Dan Lukes wrote:
> jonghwan Choi wrote:
>> "The STANDBY command (see 7.45) and STANDBY IMMEDIATE command (see 7.46) move a device to Standby mode immediately from the Active mode or Idle mode. The STANDBY command also sets the Standby timer count."
>>
>> What I understood is :
> ...
>> But If the standby command is executed with sector count non-zero, it does
>> not enter the standby mode immediately but it enters the standby mode when
>> the timer expires.
> I understand it different way. STANDBY (IMMEDIATE) command puts disk
> into Standby mode regardless the timer setting operation (e.g. all the
> times). Moreover it can modify Standby Time Counter configuration.

Correct. Both commands causes drive to enter standby mode. The STANDBY 
command also modifies the timer configuration.

These commands exist since the early days. Quote from X3T10/791D 
Revision 4c (ATA[-1], 1994):

"
9.25 Standby
This command causes the drive to enter the Standby Mode. ...

If the Sector Count Register is non-zero then the automatic power down
sequence shall be enabled and the timer will begin counting down when the
drive returns to Idle mode. If the Sector Count Register is zero then the
automatic power down sequence shall be disabled.

9.26 Standby immediate
This command causes the drive to enter the Standby Mode. ...
"

The peculiar mapping of Standby Timeout to Sector Count value was later 
added in ATA-2 (1996) and is still the same in recent ACS-4 draft (April 
2017).

AFAICS there is still no command which could modify the standby timer 
configuration without affecting the power mode itself.

Regards,
Christian


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