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Full Discussion: IRQ and Number of Devices
Special Forums Hardware IRQ and Number of Devices Post 302827005 by Lost in Cyberia on Thursday 27th of June 2013 05:46:01 PM
Old 06-27-2013
IRQ and Number of Devices

Hello everyone. I feel that I'm about to answer my own question, but I just want to be sure that I'm right. I know computers all use, at a very low level, the IRQ system of interrupting the CPU when it needs something. My questions are as follows:

1. Does the device in question, say.. a mouse, need to use the interrupt wire every single time, I use it? Say if the CPU is potentially idle, and I tap a few keys, even though the CPU wasn't busy, will it still use the interrupt feature? Or intteruppting the CPU only done when it has other things it's busy with?

2. How can there only be 16 IRQ devices? Also considering that 3 of them are already taken, (timer, keyboard, and clock) and that 2 & 9 are the same. Doesn't this mean that if I plug in 16 devices into a 20port usb hub that I'd be out of device room? Or does the usb bus count as 1 device? Same goes for SATA ports? I have 4 SATA ports on my motherboard. if I plug in 4 SATA hard drives, does that mean i'm filling up 4 seperate IRQ slots?


Thanks for the help in advance!
 

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SIIS(4) 						   BSD Kernel Interfaces Manual 						   SIIS(4)

NAME
siis -- SiliconImage Serial ATA Host Controller driver SYNOPSIS
To compile this driver into the kernel, place the following lines in your kernel configuration file: device pci device scbus device siis Alternatively, to load the driver as a module at boot time, place the following line in loader.conf(5): siis_load="YES" The following tunables are settable from the loader(8): hint.siis.X.msi controls Message Signaled Interrupts (MSI) usage by the specified controller. hint.siisch.X.pm_level controls SATA interface Power Management for the specified channel, allowing some power to be saved at the cost of additional command latency. Possible values: 0 interface Power Management is disabled (default); 1 device is allowed to initiate PM state change, host is passive. Note that interface Power Management is not compatible with device presence detection. A manual bus reset is needed on device hot-plug. hint.siisch.X.sata_rev setting to nonzero value limits maximum SATA revision (speed). Values 1, 2 and 3 are respectively 1.5, 3 and 6Gbps. DESCRIPTION
This driver provides the CAM(4) subsystem with native access to the SATA ports of controller. Each SATA port is represented to CAM as a sep- arate bus with 16 targets. Most of the bus-management details are handled by the SATA-specific transport of CAM. Connected ATA disks are handled by the ATA protocol disk peripheral driver ada(4). ATAPI devices are handled by the SCSI protocol peripheral drivers cd(4), da(4), sa(4), etc. Driver features include support for Serial ATA and ATAPI devices, Port Multipliers (including FIS-based switching), hardware command queues (31 command per port), Native Command Queuing, SATA interface Power Management, device hot-plug and Message Signaled Interrupts. The activity LEDs of the adapters supported by the siis driver can be controlled via the led(4) API for localization or status reporting pur- poses. Same hardware is also supported by the atasiliconimage driver from ata(4) subsystem. If both drivers are loaded at the same time, this one will be given precedence as the more functional of the two. HARDWARE
The siis driver supports the following controller chips: o SiI3124 (PCI-X 133MHz/64bit, 4 ports) o SiI3131 (PCIe 1.0 x1, 1 port) o SiI3132 (PCIe 1.0 x1, 2 ports) o SiI3531 (PCIe 1.0 x1, 1 port) FILES
/dev/led/siisch* identification LED device nodes SEE ALSO
ada(4), ata(4), cam(4), cd(4), da(4), led(4), sa(4) HISTORY
The siis driver first appeared in FreeBSD 8.0. AUTHORS
Alexander Motin <mav@FreeBSD.org> BSD
April 8, 2011 BSD
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