Motorola ColdFire MCF5281 - Manual (Page 155)

System Control Module (SCM)
Freescale Semiconductor 8-3
5. Chip Selects
NOTE
This is the list of memory access priorities when viewed from the processor
core.
See Figure 8-1 and Table 8-2 for descriptions of the bits in IPSBAR.
8.4.2 Memory Base Address Register (RAMBAR)
The processor supports dual-ported local SRAM memory. This processor-local memory can be accessed
directly by the core and/or other system bus masters. Since this memory provides single-cycle accesses at
processor speed, it is ideal for applications where double-buffer schemes can be used to maximize
system-level performance. For example, a DMA channel in a typical double-buffer (also known as a
ping-pong scheme) application may load data into one portion of the dual-ported SRAM while the
processor is manipulating data in another portion of the SRAM. Once the processor completes the data
calculations, it begins processing the just-loaded buffer while the DMA moves out the just-calculated data
from the other buffer, and reloads the next data block into the just-freed memory region. The process
repeats with the processor and the DMA “ping-ponging” between alternate regions of the dual-ported
SRAM.
The processor design implements the dual-ported SRAM in the memory space defined by the RAMBAR
register. There are two physical copies of the RAMBAR register: one located in the processor core and
accessible only via the privileged MOVEC instruction at CPU space address 0xC05, and another located
in the SCM at IPSBAR + 0x008. ColdFire core accesses to this memory are controlled by the
processor-local copy of the RAMBAR, while module accesses are enabled by the SCM's RAMBAR.
31 30 29 16
Field BA31 BA30 —
Reset 0 1 —
R/W R/W
15 1 0
Field — V
Reset — 1
R/W R/W
Address IPSBAR + 0x000
Figure 8-1. IPS Base Address Register (IPSBAR)
Table 8-2. IPSBAR Field Description
Bits Name Description
31–30 BA Base address. Defines the base address of the 1-Gbyte internal peripheral space. This is the
starting address for the IPS registers when the valid bit is set.
29–1 — Reserved, should be cleared.
0 V Valid. Enables/disables the IPS Base address region. V is set at reset.
0 IPS Base address is not valid.
1 IPS Base address is valid.
MCF5282 and MCF5216 ColdFire Microcontroller User’s Manual, Rev. 3