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Hardware components communicate with the Central Processing Unit or cpu over a bus. The most common buses today are usb, pci, agp, pci-express and pcmcia aka pc-card. These are all Plag and Play buses.
Older x86 computers often had isa buses, which can be configured using jumpers or dip switches.
To list the buses recognised by the Linux kernel on your computer, look at the contents of the /proc/bus/ directory (screenshot from Ubuntu 7.04 and RHEL4u4 below).
root@laika:~# ls /proc/bus/ input pccard pci usb
[root@RHEL4b ~]# ls /proc/bus/ input pci usb
Can you guess which of these two screenshots was taken on a laptop ?
To list all the usb devices connected to your system, you could read the contents of /proc/bus/usb/devices (if it exists) or you could use the more readable output of lsusb, which is executed here on a SPARC system with Ubuntu.
root@shaka:~# lsusb Bus 001 Device 002: ID 0430:0100 Sun Microsystems, Inc. 3-button Mouse Bus 001 Device 003: ID 0430:0005 Sun Microsystems, Inc. Type 6 Keyboard Bus 001 Device 001: ID 04b0:0136 Nikon Corp. Coolpix 7900 (storage) root@shaka:~#
The /var/lib/usbutils/usb.ids file contains a gzipped list of all known usb devices.
paul@barry:~$ zmore /var/lib/usbutils/usb.ids | head ------> /var/lib/usbutils/usb.ids <------ # # List of USB ID's # # Maintained by Vojtech Pavlik <vojtech@suse.cz> # If you have any new entries, send them to the maintainer. # The latest version can be obtained from # http://www.linux-usb.org/usb.ids # # $Id: usb.ids,v 1.225 2006/07/13 04:18:02 dbrownell Exp $
To get a list of all pci devices connected, you could take a look at /proc/bus/pci or run lspci (partial output below).
paul@laika:~$ lspci ... 00:06.0 FireWire (IEEE 1394): Texas Instruments TSB43AB22/A IEEE-139... 00:08.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL-816... 00:09.0 Multimedia controller: Philips Semiconductors SAA7133/SAA713... 00:0a.0 Network controller: RaLink RT2500 802.11g Cardbus/mini-PCI 00:0f.0 RAID bus controller: VIA Technologies, Inc. VIA VT6420 SATA ... 00:0f.1 IDE interface: VIA Technologies, Inc. VT82C586A/B/VT82C686/A... 00:10.0 USB Controller: VIA Technologies, Inc. VT82xxxxx UHCI USB 1.... 00:10.1 USB Controller: VIA Technologies, Inc. VT82xxxxx UHCI USB 1.... ...
An interrupt request or IRQ is a request from a device to the CPU. A device raises an interrupt when it requires the attention of the CPU (could be because the device has data ready to be read by the CPU).
Since the introduction of pci, irq's can be shared among devices.
Interrupt 0 is always reserved for the timer, interrupt 1 for the keyboard. IRQ 2 is used as a channel for IRQ's 8 to 15, and thus is the same as IRQ 9.
You can see a listing of interrupts on your system in /proc/interrupts.
paul@laika:~$ cat /proc/interrupts CPU0 CPU1 0: 1320048 555 IO-APIC-edge timer 1: 10224 7 IO-APIC-edge i8042 7: 0 0 IO-APIC-edge parport0 8: 2 1 IO-APIC-edge rtc 10: 3062 21 IO-APIC-fasteoi acpi 12: 131 2 IO-APIC-edge i8042 15: 47073 0 IO-APIC-edge ide1 18: 0 1 IO-APIC-fasteoi yenta 19: 31056 1 IO-APIC-fasteoi libata, ohci1394 20: 19042 1 IO-APIC-fasteoi eth0 21: 44052 1 IO-APIC-fasteoi uhci_hcd:usb1, uhci_hcd:usb2,... 22: 188352 1 IO-APIC-fasteoi ra0 23: 632444 1 IO-APIC-fasteoi nvidia 24: 1585 1 IO-APIC-fasteoi VIA82XX-MODEM, VIA8237
Communication in the other direction, from CPU to device, happens through IO ports. The CPU writes data or control codes to the IO port of the device. But this is not only a one way communication, the CPU can also use a device's IO port to read status information about the device. Unlike interrupts, ports cannot be shared!
You can see a listing of your system's IO ports via /proc/ioports.
[root@RHEL4b ~]# cat /proc/ioports 0000-001f : dma1 0020-0021 : pic1 0040-0043 : timer0 0050-0053 : timer1 0060-006f : keyboard 0070-0077 : rtc 0080-008f : dma page reg 00a0-00a1 : pic2 00c0-00df : dma2 00f0-00ff : fpu 0170-0177 : ide1 02f8-02ff : serial ...
A device that needs a lot of data, interrupts and ports can pose a heavy load on the cpu. With dma or Direct Memory Access a device can gain (temporary) access to a specific range of the ram memory.
Looking at /proc/dma might not give you the information that you want, since it only contains currently assigned dma channels for isa devices.
root@laika:~# cat /proc/dma 1: parport0 4: cascade
pci devices that are using dma are not listed in /proc/dma, in this case dmesg can be useful. The screenshot below shows that during boot the parallel port received dma channel 1, and the Infrared port received dma channel 3.
root@laika:~# dmesg | egrep -C 1 'dma 1|dma 3' [ 20.576000] parport: PnPBIOS parport detected. [ 20.580000] parport0: PC-style at 0x378 (0x778), irq 7, dma 1... [ 20.764000] irda_init() -- [ 21.204000] pnp: Device 00:0b activated. [ 21.204000] nsc_ircc_pnp_probe() : From PnP, found firbase 0x2F8... [ 21.204000] nsc-ircc, chip->init