-----Original Message----- From: hinko.kocevar@xxxxxxxxxxxx [mailto:hinko.kocevar@xxxxxxxxxxxx] Sent: Wednesday, July 18, 2007 12:14 PM To: rajendra.stalekar@xxxxxxxxx Cc: 'Erik Mouw'; kernelnewbies@xxxxxxxxxxxx Subject: Re: Doubt on Interrupt sharing Rajendra Stalekar wrote: > > >> Rajendra :- How can that be done? Is it not a physical interrupt > line(wire), >> how can that line go to multiple devices. > > That is the job of interrupt controller in the hardware- it multiplexes > the interrupt sources and presents them on the single interrupt number > IRQ number shown in /proc/interrupts. The way it is implemented in the > hardware differs for each architecture. When dealing with the shared > interrupts, the interrupt handler for each device driver needs to know > what hardware device caused the interrupt by means of dev_id argument > which must be unique for every device that claims the same interrupt > line (IRQ number) - hence every shared interrupt handler checks if the > interrupt was caused by the device it supports and handles the interrupt > only if it is from its device - otherwise the interrupt handler should > return IRQ_NONE and possibly let another (correct) device driver handle > the interrupt and return IRQ_HANDLED. > > Rajendra :- Thanks a lot for explanation, however what I still haven't got > is, if the interrupt line needs to be shared, since it's a hardware stuff, > shouldn't the same interrupt line have 2 wires going from the same line, one > for one device and the other for the 2nd device. How , otherwise how will it > share the interrupt line? > I am aware of the other things, that u have mentioned here. It is the job of the interrupt controller to take several physical lines, or PCB traces if you wish, each leading to *only* one device and multiplex those lines so that operating system sees them on a single IRQ number. For example take LX100 etrax CPU [1] (which I'm familiar with) that has eight physical pins - grouped together in a port called port A. Each pin of port A can be used as interrupt source and can connected to a different device. OS OTOH sees complete port A (8 all pins) on a single IRQ number 11. In order to assert which device caused the IRQ11 one needs to inspect interrupt status register of port A and its bits to determine which device actually caused the IRQ11. Several devices can assert the IRQ11 at the same time and once all the set bits in interrupt status register have been cleared all the devices have been handled. regards, hinko Rajendra :- Thanks a lot buddy, that was an excellent example. It clarified my doubt., I did some googling and found out something more on it about different types of registers used in the Programmable Interrupt Controller, so I could very well understand the register stuff. [1] www.axis.com -- ČETRTA POT, d.o.o., Kranj Planina 3 4000 Kranj Slovenia, Europe Tel. +386 (0) 4 280 66 03 E-mail: hinko.kocevar@xxxxxxxxxxxx Http: www.cetrtapot.si -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
