Rajat Jain wrote: > Hello Rene, > > Thanks for the reply. > >> On 19-08-08 07:11, Rajat Jain wrote: >> >>> 1) My first question is WHO writes that IRQ value in the device >>> configuration space? Is it hardwired on the card? Is it written by >>> the PCI controller driver or some other kernel component? Or some >>> other piece of software takes care of it? >> >> The thing hardwired on the card is the interrupt PIN(s) it >> uses; A, B, C and/or D (one pin per device and thus per >> config space). The thing that writes the LINE value into the >> register is generally the BIOS; being motherboard specific it >> knows which IRQ line it is that pin X (A, B, C or D) from >> slot N is routed to and it writes those values back into the device. >> > > OK. But who does it in an embedded environment (PPC for eg) where > there > is no POST software. The first piece of code that gets executed is > U-boot and then the kernel. So who writes the LINE value into the > config > space? > U-boot does. There is a fairly standardised way to connect PCI interrupt lines, especially for PCI slots where various cards can be plugged in: A rotation on 1 is applied to the wiring of the interrupt lines between each device/slot, order is dependant on the wiring of the device select lines, I think chapter 6 of TLK[1] has some of the basics. These rotations also need to be carried across PCI-to-PCI bridges. Hence the third device on bus 0 should have: A->INT3; B->INT4; C->INT1; d->INT2. INT[1-4] then map into a set of interrupt numbers, which are also highly dependant on the hardware. There is a lot of hardware where this doesn't hold true for onboard devices (and probably even slots) and the mapping of the devices interrupts with relation to their device select lines are provided by a board specific table. Martyn [1] http://www.tldp.org/LDP/tlk/dd/pci.html -- Martyn Welch MEng MPhil MIET Principal Software Engineer GE Fanuc Intelligent Platforms Tove Valley Business Park, Towcester, Northants, NN12 6PF, United Kingdom Telephone: +44 (0) 1327 359444 Direct Dial: +44 (0) 1327 322748 Fax: +44 (0) 1327 322800 email: martyn.welch@xxxxxxxxxxx web: www.gefanuc.com GE Fanuc Intelligent Platforms Ltd, registered in England and Wales (3828642) at 100 Barbirolli Square, Manchester, M2 3AB, VAT GB 729 849 476 GE Fanuc Intelligent Platforms Confidential and Proprietary. If you have received this message in error please notify us immediately and permanently remove it from your system and destroy any printed hardcopies. -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
