GD82559ER — Networkin g Silicon
31 | 2 1 0 | ||
Base Address |
| 0 | 1 |
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Reserved
I/O space indicator
Figure 22. Base Address Register for I/O Mapping
Note: Bit 0 in all base registers is read only and used to determine whether the register maps into memory or I/O space. Base registers that map to memory space must return a 0b in bit 0. Base registers that map to I/O space must return 1b in bit 0.
Base registers that map into I/O space are always 32 bits wide with bit 0 hardwired to a 1b, bit 1 is reserved and must return 0b on reads, and the other bits are used to map the device into I/O space.
The number of upper bits that a device actually implements depends on how much of the address space the device will respond to. For example, a device that wants a 1 Mbyte memory address space would set the most significant 12 bits of the base address register to be configurable, setting the other bits to 0b.
The 82559ER contains BARs for the Control/Status Register (CSR), Flash, and Expansion ROM.
7.1.9.1CSR Memory Mapped Base Address Register
The 82559ER requires one BAR for memory mapping. Software determines which BAR, memory or I/O, is used to access the 82559ER CSR registers.
The memory space for the 82559ER CSR Memory Mapped BAR is 4 Kbyte. It is marked as prefetchable space and is mapped anywhere in the
7.1.9.2CSR I/O Mapped Base Address Register
The 82559ER requires one BAR for I/O mapping. Software determines which BAR, memory or I.O, is used to access the 82559ER CSR registers. The I/O space for the 82559ER CSR I/O BAR is 64 bytes.
7.1.9.3Flash Memory Mapped Base Address Register
The Flash Memory BAR is a Dword register. The 82559ER physically supports up to a 128 Kbyte Flash device, and requests a 128Kbyte window. The 82559ER always claims a Flash memory window, regardless of whether or not a Flash device is connected (i.e. Flash Base Address Register cannot be disabled).
7.1.9.4Expansion ROM Base Address Register
The Expansion ROM BAR is a Dword register and supports a 128 Kbyte memory via the 82559ER local bus. The Expansion ROM BAR can be disabled by setting the Boot Disable bit of the EEPROM (word AH, bit 11). The 82559ER requests a 1MB window for expansion ROM. If the Boot Disable bit is set, the 82559ER returns a 0b for all bits in this address register, avoiding request of memory allocation for this space.
52 | Datasheet |
