[Leaplist] Help! My Ubuntu partially freezes up *after* bootup

[Bryan J. Smith]

Danny W. Burdick wrote:  
> If it's a simple case of hard drive going south....

Actually not.  ATA is a real PITA.

ATA commonly causes issues when the ...
- PC/AT Attachment (ATA) controller "dumb bus arbitrator"
- Has its register setup by the 16-bit PC BIOS/POST operation
- Which is on a 32-bit PCI (still logically for PCIe) to Memory
- Is driven, possibly memory mapped I/O by the OS
- But commands actually originate on the "Intelligent Drive
Electronics (IDE)"

The last actually does the transfer, point-to-point (drive to/from
memory).

There are about 100 things can go wrong.  Linux commonly has
"timeouts" with troublesome interaction between ATA controller -
[P]ATA/SATA IDEs on hard drives.  The "smartctl" utility can tell you
if you're actually getting media errors better than a simple syslog
entry, although it may still be the interaction.  The BIOS/POST setup
and Linux ATA support for the ATA controller can compensate, or even
fight one another at times.

Remember, the ATA controller is a "dumb bus arbitrator."  It uses a
legacy, 16-bit Industry Standard Architecture (ISA) interface, only
at 8-33MHz DDR/QDR (PATA) or 50-100MHz QDR (SATA) signaled bus into
32-bit PCI (logically for PCIe).  The hard drive itself, with its
IDE, is actually controlling all transfers.  So if the BIOS/POST
and/or OS driver doesn't setup/drive the ATA controller as the drive
expects, you can have disconnects and resets.

"Resets" are commonly due to interaction issues, not media errors. 
That's a tell tale.


-- 
Bryan J. Smith       Professional, Technical Annoyance
b.j.smith at ieee.org  http://www.linkedin.com/in/bjsmith
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