Variable 16 or 32 bit PCI interface which supports steering and swapping of data

摘要

A PCI interface is provided to support a 16- or 32-bit PCI host employing little-endian or big-endian byte ordering. The PCI interface may be arranged on a multiport switch to enable a PCI host to access internal registers and an external memory via a PCI bus. When a 16-bit PCI host is provided with access to a 32-bit internal register, two consecutive 16-bit data transfers are performed. The first 16 bits of data are temporarily stored in a holding register until the following 16 bits are transferred. The PCI host accesses the external memory via posting write buffers and prefetch read buffers arranged between an external memory interface and the PCI interface. When the multiport switch is configured to support a big-endian PCI host, bytes of a word transferred between the external memory and a write or read buffer are swapped to rearrange byte ordering of the word. A data steering means is arranged between the PCI bus and the write or read buffer to connect required pins of the PCI interface with a required location in the buffer.