Plug-and-Play BIOS spec says that if you have a PnP BIOS, it can configure the hardware.
This means that your BIOS reads the resource requirements of all devices and configures them (allocates bus-resources to them).
Does a PnP always allocate resources(ie assigns I/O or memory addresses and irqs) to the devices embedded/integrated on motherboard?
Will a PnP BIOS(ie $PnP structure is present), always assign resources(I/O and memory addresses) to all devices present on mobo(ie embedded/integrated on mobo) as well as on PCI expansion cards.
Although the BIOS may not know how to 'configure' the non-embedded devices(ie devices not embedded on mobo), and will only configure devices embedded/integrated on mobo itself, it 'should' assign addresses(I/O and memory in PCI BARs) and irq to avoid conflicts in case a non-PnP OS like DOS is to be used.
My question is:
Does a PnP BIOS must assign the I/O, memory addresses and irq to PCI expansion card devices during POST, ie before loading and transferring control to OS bootloader ? Is it true for all PnP BIOSes ?
Assume [Plug-and-Play OS] option is set to No. ie we told the BIOS that we do not have a PnP OS, but a non-PnP OS like DOS.
Some BIOSes do not have this option. Do they always allocate resources to all devices(ie both embedded ones and those on expansion slots)?
Update on 2012-08-01 :
Section 2.1 titled 'System BIOS POST Requirements' of PnP BIOS spec v1a says:
(I mentioned only the 3 points that are relevant to this post. The (*) marked info is my interpretation of the standard's statements. )
In order to achieve the goals of Plug and Play, the system BIOS POST is responsible for achieving the requirements listed below:
Configuration of all 'static' devices known to system BIOS:
At a 'minimum', this includes system board devices. It 'can' also include 'Plug and Play ISA Cards' and devices located on EISA, ISA, PCI, or any of the other static bus architectures available.
*In effect, the above statement says, devices 'embedded/integrated' on the system board on any static bus (e.g., PCI, ISA, or EISA).) 'must' be configured by the BIOS, becoz *BIOS knows about 'all' of the devices that are embedded on mobo, as a design part.* The system BIOS programmer must have incorporated the provisions to configure the devices embedded on mobo as a system design part.
Does this also include, 'cards installed in PCI/ISA/EISA card slots' ? This is where I'm confused exactly.
BIOS POST Resource arbitration: The system BIOS must now be aware of system resource usage. Using the information provided through runtime services (described in a later section), along with resource information known to the system BIOS, critical resource conflicts can be avoided. 'Loading the operating system with a conflicting device disabled is better than causing a resource conflict and a possible system failure.'
*This seems for ISA/EISA devices embedded/integrated on mobo or on ISA/EISA expansion card slots. Since PCI devices' resources can't conflict in terms of both I/O( or memory) address allocation(becoz the addresses are not hardwired for PCI devices, and hence in the 'hands' of BIOS to allocate non-conflicting addresses.) and irq allocation(becoz PCI interrupts are shareable by design.), so this means that 'all' PCI devices(embedded or non-embedded)will be initialized/allocated memory or I/O addresses and irq assigmnments.
Support for both Plug and Play and Non-Plug and Play Operating Systems: The Plug and Play system BIOS POST 'must' configure the system to operate with 'both' Plug and Play aware, 'as well as' non-Plug and Play operating system.* In non-Plug and Play environments, 'either' the system BIOS 'or' the appropriate system software (device drivers) 'must' configure 'all' devices (Plug and Play ISA Cards, PCI devices, etc.). This will allow all environments to 'load exactly as they would on a standard PC compatible systems'. However, in a Plug and Play environment, the system BIOS can now assist the operating system to perform features such as runtime configuration of system board devices and event recognition when system board devices have changed.
*All these 3 statements from the spec, seems to point that if a non-PnP OS is to be booted(e.g. DOS), then the system BIOS 'must' configure( or, allocate addresses and irqs, at least) 'all' PCI devices, whether embedded/integrated on motherboard(mobo) or not. For ISA and EISA devices, the BIOS 'must' not enable/allocate the resources for those ISA/EISA devices(whether embedded or non-embedded) which will result in conflicting resource assignments.
Am I right in concluding that: "If the BIOS must boot a non-PnP OS, it must enable (i.e., enable ie allocate resources) 'every' PCI device(whether embedded on mobo or on PCI expansion card slot) in the system so that they are available for use by the OS and application programs"?
At least this must be the case when [Plug-and-Play OS] option is set to NO. ie we told the BIOS that we do not have a PnP OS, but a non-PnP OS like DOS.