Freescale Semiconductor MCF5480 - Manual (Page 225)

SRAM Initialization
MCF548x Reference Manual, Rev. 3
Freescale Semiconductor 7-5
3. After the data is loaded into the SRAM, it may be appropriate to revise the RAMBAR attribute
bits, including the write-protect and address-space mask fields. If the SRAM contains
instructions, RAMBAR[D/I] must be set to logically connect the memory to the processor’s
internal instruction bus.
Remember that the SRAM cannot be accessed by the on-chip DMAs. The on-chip system configuration
allows concurrent core and DMA execution, where the core can execute code out of internal SRAM or
cache during DMA access.
The ColdFire processor or an external emulator using the debug module can perform these initialization
functions.
7.5.1 SRAM Initialization Code
The code segment below initializes the SRAM using RAMBAR0. The code sets the base address of the
SRAM at 0x2000_0000 before it initializes the SRAM to zeros.
RAMBASE EQU 0x20000000 ;set this variable to 0x20000000
RAMVALID EQU 0x00000035
move.l #RAMBASE+RAMVALID,D0 ;load RAMBASE + valid bit into D0
movec.l D0, RAMBAR0 ;load RAMBAR0 and enable SRAM
The following loop initializes the entire SRAM to zero:
lea.l RAMBASE,A0 ;load pointer to SRAM
move.l #1024,D0 ;load loop counter into D0
SRAM_INIT_LOOP:
clr.l (A0)+ ;clear 4 bytes of SRAM
subq.l #1,D0 ;decrement loop counter
bne.b SRAM_INIT_LOOP ;exit if done; else continue looping
The following function copies the number of bytesToMove from the source (*src) to the processor’s local
SRAM at an offset relative to the SRAM base address defined by destinationOffset. The bytesToMove
must be a multiple of 16. For best performance, source and destination SRAM addresses should be
line-aligned (0-modulo-16).
; copyToCpuRam (*src, destinationOffset, bytesToMove)
RAMBASE EQU 0x20000000 ;SRAM base address
RAMFLAGS EQU 0x00000035 ;RAMBAR valid + mask bits
lea.l -12(a7),a7;allocate temporary space
movem.l #0x1c,(a7);store D2/D3/D4 registers
; stack arguments and locations
; +0
saved d2
; +4 saved d3
; +8 saved d4
; +12 returnPc
; +16 pointer to source operand