[smartmontools-support] problem with scterc on a mac

[Dennis Couzin]

Dear Christian,
Thank you for quoting from the later versions.
The ACS-4 version finally says enough.  It replaces the expression "default value" with two expressions: 
	"Power-on Read Command Timer value";
	"Power-on Write Command Timer value".
Then you get to read clauses like:
	"The Read Command Timer shall be set to the value of the Power-on Read Command Timer ..."
I pity whoever must read such verbose specifications.  A bit of mathematical or logical syntax makes much bigger ideas than these much clearer.

Why did ACS-4 want ERC values settings not to persist through a power-on reset, since power-ons are normal events in a drive's life? 
Shouldn't default ERC values, like other default values, only be restored by intentional resettings?
I think I prefer Toshiba's misunderstanding of the specification.

Sincerely,
Dennis

-----Original Message-----
From: Smartmontools-support <smartmontools-support-bounces at listi.jpberlin.de> On Behalf Of Christian Franke
Sent: Monday, 10 February 2020 18:41
To: Dennis Couzin <dcouzin at yahoo.com>
Cc: Smartmontools-support at listi.jpberlin.de
Subject: Re: [smartmontools-support] problem with scterc on a mac

Dennis Couzin wrote:
> Your quote from the 2008 ATA8-ACS final draft:	
> 	"Read and Write Command Timer values are set to default values at
> 	power-on but may be altered by an SCT command at any time. A device
> 	shall not change these settings while processing a hardware reset or a
> 	software reset."
> The phrase "these settings" in the second sentence is ambiguous: it can refer either to the default values mentioned in the first sentence or to the altered values mentioned later in the first sentence.  To a normal, untechnical English reader, "these settings" would refer to the altered values.  On that reading, if a "power-on" entails a "reset", the second sentence contradicts the first.  But if a "power-on" does not entail a "reset", there will be no contradiction.

ATA standards specify 3 kinds of resets: "power-on reset", "hardware 
reset" and "software reset".

ACS-2 changed the text "... at power-on ..." to "... after processing a 
power-on reset ...".

ACS-4 enhanced this to:
"The Read Command Timer value and the Write Command Timer value persist 
across a hardware reset and a software reset. The Power-on Read Command 
Timer value and the Power-on Write Command Timer value persist across 
all resets (e.g. power-on reset). The Read Command Timer shall be set to 
the value of the Power-on Read Command Timer as a result of processing a 
power-on reset. The Write Command Timer shall be set to the value of the 
Power-on Write Command Timer as a result ofprocessing a power-on reset. "


> Ca. 2008, WD supplied a DOS program wdler.exe to make ERC settings on its hard drives.  Could its settings have been anything but "persistent"?

This tool might use vendor specific commands. Therefore persistence may 
differ from the standard commands.

Regards,
Christian

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