Configuration and RAM/ROM control of PCI extension card residing on MCA adapter card

摘要

Method and apparatus for enabling configuration of a PCI daughter card residing on an MCA adapter card using MCA setup cycles and signals and for ensuring the allocation of memory space to the daughter card. In a preferred embodiment, the invention comprises an MCA adapter card connected to an MCA system bus of a conventional PC. A PCI-compliant daughter card, the purpose of which is to provide additional functionality to circuitry of the adapter card, resides on a PCI bus of the adapter card. A PCI/MCA bridge is provided for interfacing the MCA system bus with the PCI bus of the adapter card for enabling configuration of the daughter card during the setup sequence of the MCA bus and to respond with an appropriate ROM signature during DOS boot-up to ensure that memory space will be allocated to the daughter card, if needed. A first set of XPOS registers of the adapter card are used selectively to enable the bridge and to allow the PCI configuration space, or registers, of the daughter card and other PCI-compliant devices on the daughter card to be selectively accessed and initialized. Certain registers of a second set of XPOS registers are used to set the data flow mode of the bridge and to respond with the correct ROM signature at DOS boot-up of the PC. The remaining ones of the second set of XPOS registers are used selectively to enable and to store the size and location of any necessary RAM and/or ROM apertures of the daughter card, thereby enabling the bridge to initiate a PCI operation to the daughter card if it decodes an address within either of the apertures.