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Static RAM (SRAM)
7-4
Freescale Semiconductor
7.3
Initialization/Application Information
After a hardware reset, the SRAM module contents are undefined. The valid bit of the RAMBAR is
cleared, disabling the processor port into the memory. RAMBAR[BDE] is set, enabling the system
backdoor port into the memory. If the SRAM requires initialization with instructions or data, perform the
following steps:
1. Load the RAMBAR, mapping the SRAM module to the desired location within the address space.
2. Read the source data and write it to the SRAM. Various instructions support this function,
including memory-to-memory move instructions, or the MOVEM opcode. The MOVEM
instruction is optimized to generate line-sized burst fetches on 0-modulo-16 addresses, so this
opcode generally provides maximum performance.
3. After the data loads into the SRAM, it may be appropriate to load a revised value into the
RAMBAR with a new set of attributes. These attributes consist of the write-protect and address
space mask fields.
The ColdFire processor or an external debugger using the debug module can perform these initialization
functions.
7.3.1
SRAM Initialization Code
The following code segment describes how to initialize the SRAM. The code sets the base address of the
SRAM at 0x8000_0000 and initializes the SRAM to zeros.
RAMBASE
EQU 0x80000000
;set this variable to 0x80000000
RAMVALID EQU
0x00000001
5–1
C/I, SC, SD, UC,
UD
Address Space Masks (AS
n
). These five bit fields allow types of accesses to be masked or inhibited from
accessing the SRAM module. The address space mask bits are:
C/I = CPU space/interrupt acknowledge cycle mask
SC = Supervisor code address space mask
SD = Supervisor data address space mask
UC = User code address space mask
UD = User data address space mask
For each address space bit:
0 An access to the SRAM module can occur for this address space
1 Disable this address space from the SRAM module. If a reference using this address space is made, it
is inhibited from accessing the SRAM module and is processed like any other non-SRAM reference.
These bits do not affect accesses by non-core bus masters using the SRAM backdoor port in any manner.
These bits are useful for power management as detailed in
Section 7.3.2, “Power Management.”
In most
applications, the C/I bit is set
0
V
Valid. When set, this bit enables the SRAM module; otherwise, the module is disabled. A hardware reset
clears this bit.
0 Processor accesses of the SRAM are masked
1 Processor accesses of the SRAM are enabled
Table 7-2. RAMBAR Field Descriptions (continued)
Field
Description
Summary of Contents for MCF54455
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Page 145: ...Enhanced Multiply Accumulate Unit EMAC 5 21 Freescale Semiconductor ...
Page 173: ...Cache 6 28 Freescale Semiconductor ...
Page 179: ...Static RAM SRAM 7 6 Freescale Semiconductor ...
Page 207: ...Power Management 9 16 Freescale Semiconductor ...
Page 323: ...Reset Controller Module 13 8 Freescale Semiconductor ...
Page 389: ...Pin Multiplexing and Control 16 44 Freescale Semiconductor ...
Page 575: ...PCI Bus Controller 22 58 Freescale Semiconductor ...
Page 600: ...Advanced Technology Attachment ATA Freescale Semiconductor 23 25 ...
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