From: bugzilla-daemon@bugs.ecos.sourceware.org
To: ecos-patches@ecos.sourceware.org
Subject: [Bug 1001174] New: i386 PC floppy boot fails in Bochs and with some real BIOSes
Date: Wed, 16 Mar 2011 17:49:00 -0000 [thread overview]
Message-ID: <bug-1001174-104@http.bugs.ecos.sourceware.org/> (raw)
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Summary: i386 PC floppy boot fails in Bochs and with some real
BIOSes
Product: eCos
Version: CVS
Platform: pc (i386 PC target)
OS/Version: IA32
Status: UNCONFIRMED
Severity: enhancement
Priority: low
Component: Patches and contributions
AssignedTo: unassigned@bugs.ecos.sourceware.org
ReportedBy: horst@schirmeier.com
CC: ecos-patches@ecos.sourceware.org
Class: Advice Request
Created an attachment (id=1175)
--> (http://bugs.ecos.sourceware.org/attachment.cgi?id=1175)
pcmb.inc: enable interrupts before waiting for the BIOS
In Bochs (releases 2.3.7 and 2.4.5, and current SVN head -r10265) and on some
(but by far not all) tested PCs, eCos (2.0, 3.0, and CVS head as of 2011-03-16)
does not boot but stalls after printing a line of dots. Further analysis
showed that the boot process is stuck in
packages/hal/i386/pcmb/current/include/pcmb.inc in this loop beginning at line
223 (as of eCos 3.0):
/* Lets be nice and wait for the diskette drive motor to go off
* before continuing. */
movw $0x40, %ax
movw %ax, %es
movl $0x40, %ebx
2: es
movb (%bx), %al
cmpb $0, %al
jne 2b
eCos polls for the BIOS data area variable at 0040:0040 to become zero, as an
indication that the INT08 handler has switched off the floppy drive motor.
Unfortunately, the Bochs BIOS (and supposedly a number of real-world BIOSes,
too) passes control to boot sector with the Interrupt Enable Flag (IF) in
EFLAGS disabled, and the timer interrupt is never triggered. Therefore the
variable won't turn 0, the drive motor never gets switched off, and eCos
stalls.
One fix is to enable interrupts right before entering the polling loop (see
attached patch), or to switch off the drive motor by yourself (out 0x0 to the
floppy drive's Digital Output Register 0x3F2, cf.
http://wiki.osdev.org/Floppy_Disk_Controller). The latter variant would remove
the 2s waiting time until the BIOS counter times out.
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next reply other threads:[~2011-03-16 17:49 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-03-16 17:49 bugzilla-daemon [this message]
2011-03-18 8:22 ` [Bug 1001174] " bugzilla-daemon
2011-03-18 8:22 ` bugzilla-daemon
2011-03-20 15:29 ` bugzilla-daemon
2011-07-02 10:04 ` bugzilla-daemon
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