Date: Sun, 5 Jul 1998 18:23:32 +0930 From: Greg Lehey <grog@lemis.com> To: "Oles' Hnatkevych" <gnut@cki.ipri.kiev.ua>, All <freebsd-questions@FreeBSD.ORG> Subject: Re: UDMA Message-ID: <19980705182332.J18970@freebie.lemis.com> In-Reply-To: <359E52B8.A54762F5@cki.ipri.kiev.ua>; from Oles' Hnatkevych on Sat, Jul 04, 1998 at 07:05:12PM %2B0300 References: <359E52B8.A54762F5@cki.ipri.kiev.ua>
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On Saturday, 4 July 1998 at 19:05:12 +0300, Oles' Hnatkevych wrote: > Hello! > > I've got ASUS TX motherboard and UDMA hard drive. > Is there any benefit from this for FreeBSD? ;-) Yes. To quote a recent message: On Monday, 29 June 1998 at 16:39:49 -0400, Christopher Wood wrote: > I'm considering putting together a low-end pentium machine to run > fBSD on... I want to go SCSI, but Ultra-DMA would be much > cheaper. Can fBSD utilize Ultra-DMA hardware? And if I want to use > this machine for CD copying, would I still need SCSI, or would UDMA > be sufficient? UDMA is supported, and it brings a *great* improvement. A non-DMA IDE system with a low-end Pentium will max out at about 500 kB/s, at which point the system will be using 90% interrupt time, making the system almost useless. The same machine with UDMA would use about 1% or 2% interrupt time with full disk throughput (which on modern disks can be over 6 MB/s). Unless you have a large number of disks, you won't see any improvement from UDMA to SCSI, and you may even see a performance decrease. To enable UDMA, set the disk driver flags, either in the visual config at boot time, or (preferably) in your kernel config file. Here's an excerpt from "The Complete FreeBSD", second edition (http://www.cdrom.com/titles/os/bsdbook2.htm), page 264 (with the latest addendum). In practice, you can almost always just set the flags word to 0xe0ffe0ff. A number of flags and options apply to wdc0: o The flags fields are used to enable the multi-sector I/O and the 32 bit I/O modes. You can use them either in the controller definition or in the individual disk definitions. If you want to use them during boot configuration, specify them in the controller definition. 16 flag bits are provided for each drive. The first 16 flag bits refer to drive 1, and the second 16 bits refer to drive 0. In each set of flags, o Bit 15 (0x8000) specifies to probe for 32 bit transfers. o Bit 14 (0x4000) enables waking powered-down laptop drives. o Bit 13 (0x2000) allows probing for PCI IDE DMA controllers, such as Intel's PIIX south bridges. o Bit 12 (0x1000) enables LBA (logical block addressing mode). If this bit is not set, the driver accesses the disk in CHS (cylinder/head/sector) mode. o In CHS mode, if bits 11 to 8 are not equal to 0, they specify the number of heads to assume (between 1 and 15). The driver recalculates the number of cylinders to make up the total size of the disk. o The low 8 bits specify the maximum number of sectors per transfer. The special case 0xff represents the maximum transfer size which the drive can handle. See the man page for wd(4) (on your system, but not in this book) for more details. Thus, we can break down the example value 0xff8004 (the full 32 bits are 0x00ff8004) into 0x00ff for drive 1 (use the maximum transfer size) and 0x8004 for drive 0 (allow probing for 32 bit support, and use a transfer size of 4 sectors). Greg -- See complete headers for address and phone numbers finger grog@lemis.com for PGP public key To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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