XC2200 Derivatives
System Units (Vol. 1 of 2)
Memory Organization
User’s Manual
3-52
V2.1, 2008-08
MemoryX2K, V1.3
instructions on the predicted branch in advance. In case of a misprediction this interface
can abort outstanding requests and continues fetching on the correct branch. As the
CPU can consume up to one 32-bit instruction per clock cycle the performance of this
interface determines the CPU performance.
The data bus is controlled by the data management unit “DMU” of the CPU. It reads data
in words of 16 bits. Write accesses address as well 16-bit words but additional byte
enables allow changing single bytes.
Because of the CPU’s “von Neumann” architecture data and instructions (and “special
function registers” to complete the list) share a common address range. When
instructions are used as data (e.g. when copying code from an IO interface to the
PSRAM) they are accessed via the data bus. The pipelined behavior of the CPU can
cause that code fetches and data accesses are requested simultaneously. The IMB
takes care that accesses can perform concurrently if they address different memories or
flash modules.
Additional connections of the IMB to central system control units exist. These are not
shown in the block diagram.