Thursday, November 24, 2011

Exception Emask { DRDY }

ata1.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x2 frozen
ata1.00: cmd a0/00:00:00:24...
ata1.00: status: {DRDY}
This fine message (or something to that effect) greeted me today upon booting up a new kernel. The message repeated itself several times, with long delays between each repetition. Eventually the system (Debian "squeeze") would boot.

Delving deeper, it seemed that the system could not find or use the DVD/RW drive, yet the kernel could see it:

# grep DVD /var/log/messages | tail -n 1
Nov 24 22:50:10 f216 kernel: [ 1.991176] scsi 0:0:1:0: CD-ROM HL-DT-ST DVD-RAM GSA-H55N 1.00 PQ: 0 ANSI: 5

In addition to the repeated "Exception emask" messages appearing at boot time, I found these messages in the relevant log file:

# cat /var/log/messages
. . .
Nov 24 22:48:39 f216 kernel: [ 245.908016] ata1: link is slow to respond, please be patient (ready=0)
Nov 24 21:27:39 f216 kernel: [   43.828023] ata1: device not ready (errno=-16), forcing hardreset
Nov 24 21:27:39 f216 kernel: [   43.828034] ata1: soft resetting link
Nov 24 21:27:39 f216 kernel: [   44.016568] ata1.01: configured for UDMA/66
Nov 24 21:27:39 f216 kernel: [   44.017812] ata1: EH complete
. . .
That's odd. Looking around on the 'net, I found lots of references to this possibly being an ACPI problem. Since the messages appeared when I installed a new kernel, I thought maybe this was due to a kernel bug. You know, when everything is working and then you upgrade the kernel and suddenly something stops working. For example, when a bug in the kernel's floppy driver nearly drove me crazy last year:

Blog entry referring to kernel floppy bug

I tried adding the "acpi=off" boot parameter (boot option) to the kernel, but that made no difference. Another possible explanation was that the DVD/RW drive suddenly went on the blink or died.

The "solution": Well, this time the kernel wasn't the culprit - I was. Prior to rebooting to activate the new kernel, I had been burning a CD-R and aborted the burn process early into the burn. I had hoped that I aborted it early enough that the CD-R would still be OK. But it wasn't OK, and it was still in the drive. I had forgotten this because the computer base unit was in the basement. When I went down there and examined the drive, I noticed that the drive activity light was on continually, and the drive was emitting strange noises. It didn't react to pressing the eject button.

So I powered down the computer and used a paper clip to force open the drive, removed the defective disc, and turned the computer back on.

The strange messages disappeared and everything went back to normal.

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