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Chapter 1: Hardware Description
4538 Hardware Reference Manual 25
On the 4538 board, the serial EEPROM content disables the windows. By default, no Local
to PCI window is enabled. It is not recommended using these windows for transfers from
or to the PCI local space, because this mechanism can result in bad performance, depending
on the other PCI devices tied to the PCI bus.
The local base address of each window is defined in PowerSpan internal register
PB_SIx_BADDR. Note that the window must be mapped in the local space between
0xC0000 0000 and 0xCFFF FFFF, in order to comply with the card local space usage. Each
window can be moved on the PCI memory or I/O space, using a PowerSpan translation
register (PB_SIx_TADDR), so that even a small window can allow access to any part of
the PCI space.
During a PowerQUICC II access to the PCI space, the high-order address bits on the PCI
bus are generated by the PowerSpan (as defined in the PowerSpan PB_SIx_BADDR
register) and the low-order address bits on the PCI bus come from the local address. This
mode is called “Address Translation” in the PowerSpan Manual.
NOTE
A PowerSpan Local-to-PCI window must be enabled in the PB_SIx_CTL register. Bits
IMG_EN (“Image Enable”) and TA_EN (“address translation enable”) must be set.
Figure 1-5 on page 26 illustrates the Local-to-PCI window mechanism: