Vmebus Master - DEC Digital Alpha VME 4/224 User Manual

The VME interface serves the following purposes:
• As a VMEbus master, it controls PCI bus-to-VMEbus, or outbound,
transactions
• As a VMEbus slave, it handles VMEbus-to-PCI bus, or inbound, transactions
and interprocessor communication.
• It can be configured as the VME system controller, handling functions such as
arbitration of bus ownership.
• It handles interrupts to the VMEbus, as an interrupter and an interrupt
servicing agent.
The VME interface conforms to the IEC 821, IEEE1014-1987, and D64 sections of
IEEE1014 Rev.D (draft) standards.
This chapter:
• Describes VME master and slave operation as well as its other roles
• Describes the procedures for initalizing the VME interface
• Summarizes all the VME interface registers

10.1 VMEbus Master

Digital Alpha VME 4 supports VME address spaces A16, A24, and A32, using two
address windows to map from PCI memory space to VME address space:
• VME_WINDOW_1 is a 512 MB address window positioned in PCI memory
space, divided into 2048 KB x 256 KB pages. Each page is mapped to VME
address space by its own scatter-gather entry. The scatter-gather entries of
the first 256 pages are also used to map the VME_WINDOW_2 pages.
• VME_WINDOW_2 is a 64 MB address window positioned in PCI memory
space, divided into 256 KB x 256 KB pages. These pages are mapped by
the same scatter-gather entries that mapped the first 256 pages in VME_
WINDOW_1. The VME_WINDOW_2 address allows support of "sparse space"
access to the VMEbus.
Each of the first 256 scatter-gather entries maps two pages to the same VME
address: a unique page within the VME_WINDOW_1 address window and an
overlapped page within the VME_WINDOW_2 address window. For example,
Entry 5 of the outbound scatter-gather RAM maps both page 5 of VME_
WINDOW_1 and page 5 of VME_WINDOW_2 to exactly the same VME address.
10–2 VME Interface