Configuration SpaceBCM5718 Programmer’s Guide
Broadcom®
January 29, 2016 • 5718-PG108-R Page 169
Most host device drivers use register blocks, which are mapped into host memory. Memory Mapped I/O is an
efficient mechanism for PCI devices to use system resources. The type and extent of this memory mapping
depends upon the MAC’s configuration (see the operational characteristics subsection). A typical PCI device
will decode a range of physical (bus) addresses, which do not conflict with physical memory or other PCI
devices. Each device on the PCI bus will request a range of physical memory, and the PnP BIOS will assign
mutually exclusive resources to that device. The size and range of resource is based upon each device’s
hardwired programming of the BAR. The Ethernet controller implements two modes of memory mapped I/O—
Standard and Flat. I/O mapped I/O is not supported by the Ethernet controller, and there are no I/O space
registers.
Two programmable blocks expose Ethernet controller functionality to host software. The first is a register block.
The second is a memory block. The register and memory blocks map into address spaces based on processor
context. For example, the Ethernet controller has an on-chip RISC processor. This RISC processor will have an
internal view of the register and memory blocks. This view is one large contiguous and addressable range,
where the register block maps starting at offset 0xC0000000. Conversely, host processors have two entirely
different views. When the Ethernet controller is configured in standard mode, the register block is mapped into
a 64K host memory range. The host processor must use a memory window or indirect mode to access the
memory block. It is fundamental to understand that the register and memory blocks are not necessarily tied
together. The PCI mode and processor context all affect how software views both blocks (see Figure 32 on page
170).
Note: The PCI BAR 0 register is only reset to 0 after a hard reset, otherwise it maintains its value over
GRC and PCI resets.
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