Re: Clarification on IO Operations

From: Gary Kato (garykato_at_aol.com)
Date: 12/29/04 

Date: 29 Dec 2004 08:56:18 GMT

>How Processor recognizes different IO devices based on Port
>numbers??

Ona hardware level, a CPU itself doesn't differentiate one device from another
any more than it knows the difference between one memory location from another.
Is location 1000 and 8000 in the same chip or in different ones? The CPU
doesn't know.

>Where these port addresses (corresponding to All IO devices) are
>stored???

Address decoding, like that of memory, is done in hardware. Sometimes this can
be done simply by looking at a few of the I/O address lines to decode which
hardware device to activate. Most designs use a Programmable Logic Device (like
a GAL) for more complex address decoding.

>Can a port shared between 2 devices???
There must be some way to say which device is being talked to. A port could be
shared if there is a bit in the port that is perhaps 0 for talking to one
device and 1 for talking to another device.

>How a hardware manufacturer come to know which port is free and can
>be used???
For a custom design, there's no problem. The hardware designer can use any port
they want. For such things like a PC, there are certain standards that have
evolved over the years. As this evolved, there were many conflicts where
companies used the same port for different devices. But most PC I/O boards had
a set of switches that one could change the port number.

Relevant Pages

  • RE: [Full-Disclosure] Microsoft urging users to buy Harware Firewalls
    ... connections between multiple computers. ... A Linksys NAT router box is selling for only $40 at Amazon ... Besides protecting against the MSBlaster worm, a hardware ... Then the user finds about port forwarding, and as soon as the user ...
    (Full-Disclosure)
  • RE: Hardware/Software Solution for Standalone DSL User
    ... A cable/DSL router is not a real "hardware security solution". ... Port filtering only works if used, if set up properly, and then only if ... the connection is using ports you don't allow through. ... A hardware solution such as a Cisco PIX 501 does more than NAT. ...
    (Security-Basics)
  • Re: System hangs up every day
    ... I would suggest examining the hardware components, ... The server works as: ... <ACPI PCI bus> on pcib0 ... port may not be enabled ...
    (freebsd-stable)
  • RE: System hangs up every day
    ... I would suggest examining the hardware components, ... There is one FreeBSD server in our company. ... <ACPI PCI bus> on pcib0 ... port may not be enabled ...
    (freebsd-stable)
  • Boot loop & ACPI BSODs with SP3 with ASUS mobo
    ... CMOS and then go in Bios and disable APM and serial port. ... If you try to install Win XP SP3 a USB drive or a USB stick on a USB ... I still have ACPI compliant computer, ... One of three types of problems occurred in kernel-mode: Hardware ...
    (microsoft.public.windowsxp.help_and_support)