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  · DriverStudio          Accessing Bus Configuration Space in WDM
  · DriverBundle
  · Previews              A sometimes overlooked aspect of Win32 Driver Model is that
  · Compatibility         access to bus configuration space, provided by HAL calls
 [Downloads]  ·           under Windows NT 4.0, is provided by system bus drivers.
 Wizards                  For example, consider the PCI bus. To read and write the PCI
  · Utilities             configuration space under NT 4.0, a driver called
  · NT source             HalGetBusDataByOffset and HalSetBusDataByOffset. These two
 examples                 calls belong to a set of services that are available on
  · VxD source            Windows 98, but whose prototypes do not appear in wdm.h. A
 examples                 driver that includes the prototypes (which can still be
  · WDM source            found in ntddk.h) can call these services, but clearly the
 examples                 use of these services is discouraged.
 [Resources]  ·
 Technical papers         The WDM way to access the configuration space is by sending
  · Useful links          a request to the bus driver. A WDM driver always
  · Technical tips        communicates with the bus driver through a Physical Device
 [Support]  ·             Object, or PDO. PDOs are the data structures that the system
                          uses to dynamically model its configuration. A bus driver
 Support                  creates a PDO for each physical device that it detects. A
  · Knowledge base        device driver receives from the system a pointer to the PDO
  · Problem               of each device that the driver controls. When the device
 submission               driver needs to read the configuration space of a device, it
  · Product               sends to the PDO for that device a request of type
 registration             IRP_MJ_PNP, with minor function IRP_MN_READ_CONFIG.
  · Release notes         Similarly, IRP_MN_WRITE_CONFIG is used for write operations.
 [Shop NuMega]  ·         The request is routed to the bus driver, which is the driver
 Buy it!                  responsible for the PDO.
  · Price list
  · How to buy            The parameter structure for this IRP bears a close
  · Sales offices         resemblance to the parameters for the Hal calls:

                          struct {
 [Y2K Compliance]                 ULONG WhichSpace;
                                  PVOID Buffer;
                                  ULONG Offset;
 [More information]               ULONG Length;
                          } ReadWriteConfig;

                          A driver simply sets up the IRP and calls the PDO. Here is
                          some Driver::Works code that demonstrates the usage of this
                          IRP:

                          ULONG ReadConfigSpace(
                                  PDEVICE_OBJECT TopOfStackDevice,
                                  PVOID Buffer,
                                  ULONG Offset,
                                  ULONG Count
                                  )
                          {
                                  ASSERT (TopOfStackDevice != NULL);
                                  NTSTATUS status;

                                  KPnpLowerDevice Ld(TopOfStackDevice, NULL, &status);

                                  KIrp I ( KIrp::Allocate(Ld.StackRequirement()) );
                                  PIO_STACK_LOCATION pStack = I.NextStackLocation();
                                  ULONG info=0;

                                  pStack->MajorFunction = IRP_MJ_PNP;
                                  pStack->MinorFunction = IRP_MN_READ_CONFIG;

                                  pStack->Parameters.ReadWriteConfig.WhichSpace = 0;
                                  pStack->Parameters.ReadWriteConfig.Buffer = Buffer;
                                  pStack->Parameters.ReadWriteConfig.Offset = Offset;
                                  pStack->Parameters.ReadWriteConfig.Length = Count;

                                  status = Ld.CallWaitComplete(I, TRUE, &info);

                                  KIrp::Deallocate(I);
                                  return info;
                          }

                          Architecturally, using system bus drivers to read and write
                          configuration space has some clear advantages. By decoupling
                          the functionality of the various buses, the system is made
                          more modular and flexible. Furthermore, using an IRP-based
                          interface rather than a procedural interface enables lower
                          filter drivers to supplement or alter the functionality of
                          the system.

                          Back to technical tip start page.

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