Messages in this thread |  | | Subject | Re: ISA I/O port programming question... | Date | Mon, 13 Jan 1997 11:16:09 PST | From | Tim Wright <> |
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Someone replied saying you cannot use the ports above 0x3ff. They are mistaken. You cannot use 3/4 of them due to the corner cutting on early cards which only decoded the lower 10-bits of the address bus, BUT ports 0x0-0xff are reserved for the motherboard and have been decoded properly since very early machines, so you can safely use 0x400-0x4ff, 0x800-0x8ff ... 0xfc00-0xffff. EISA cards use 0xN000-0xN0ff where N = the slot number to access the cards. A quick look at some of the EISA device drivers will confirm this, so in a nutshell, you can design a card to use high port numbers safely provided you remember the above.
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In message <Pine.BSI.3.95.970112201211.5837A-100000@gold.interlog.com>,Robert E rlich writes: > Hello all; > > I wonder if there are any of you in kernel land that might be able to help > me with this, as it is less a kernel question (although it does involve > creating a driver) and more a hardware question. > > I am adapting a servo motor controller board to the ISA buss. (it was > originally designed for the New Micros NMIS microcontroller family) I > would like to place it in an I/O space far away from my other periphs.; > ie. 65535 >= port >=1024. > > What is the magic of I/O ports below 0x3FF on the ISA buss? Some texts I > have read state that only the first 10 bits of the I/O address are decoded > onto the ISA buss. Is this true? Do addresses that > are higher wrap around? Are the address lines available to create > hardware that decodes to a >=1024 I/O address? If not, what happens if I > outb(0x400, 0xXX)? All these questions.... > > Thanks in advance > > Robert > ... > -- Tim Wright, Worldwide Technical Services, | Email: timw@sequent.com Sequent Computer Systems Inc., 15450, | SW Koll Parkway, Beaverton, Oregon 97006 | Phone: +1-503-578-3822 "Applying computer technology is simply finding the right wrench to pound in the correct screw"
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