Date: Mon, 19 May 2008 10:32:02 -0400 From: John Baldwin <jhb@freebsd.org> To: freebsd-hackers@freebsd.org Cc: RW <fbsd06@mlists.homeunix.com> Subject: Re: i386 cpu_reset_real: code/comment mismatch Message-ID: <200805191032.03134.jhb@freebsd.org> In-Reply-To: <20080512182328.09a8a173@gumby.homeunix.com.> References: <4828557B.9000506@icyb.net.ua> <20080512182328.09a8a173@gumby.homeunix.com.>
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On Monday 12 May 2008 01:23:28 pm RW wrote: > On Mon, 12 May 2008 17:34:35 +0300 > > Andriy Gapon <avg@icyb.net.ua> wrote: > > This is not a real issue, just a code clarification. > > > > First a snippet from sys/i386/i386/vm_machdep.c, cpu_reset_real() > > /* > > * Attempt to force a reset via the Reset Control register at > > * I/O port 0xcf9. Bit 2 forces a system reset when it is > > * written as 1. Bit 1 selects the type of reset to attempt: > > * 0 selects a "soft" reset, and 1 selects a "hard" reset. We > > * try to do a "soft" reset first, and then a "hard" reset. > > */ > > outb(0xcf9, 0x2); > > outb(0xcf9, 0x6); > > > > I think that the comment is correct up to but not including the last > > sentence. Writing 0x2 sets bit 1 to 1 (thus selecting hard reset), and > > writing 0x6 sets both bits 2 and 1 to 1 (thus performing hard reset). > > So we always just do a hard reset, no trying of soft reset (would it > > even make sense to do the last line of the comment says). > > It looks to me as if the comment was added retrospectively by someone > who got the two bits mixed-up when reading the source. If bits 1 and 2 > were the other way around, it would be code for a soft-reset followed > by a hard-reset. Or I just fubar'd the code. The comment and code were added at the same time and it should do a soft reset first. I'll have to go check the docs again to see which is wrong (comment or code). -- John Baldwin
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