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ADSP-BF533 Blackfin® Booting Process (EE-240) Page 6 of 28
When the on-chip Boot ROM detects a block with the INIT bit set, it will first boot it into Blackfin
memory and then execute it, by issuing a
CALL to its target address. For this reason, you must terminate
the Init Code with an
RTS instruction to ensure that the processor vectors back to the on-chip Boot ROM
for the rest of the boot process.
L
It is your responsibility to save all processor registers modified by Init Code and to restore them
before the Init Code returns. At a minimum, it is recommended that every Init Code saves the
ASTAT, RETS, and all Rx and Px registers. The Blackfin processor provides sufficient stack space in
scratchpad memory (0xFFB0 0000 – 0xFFB0 0FFF). The Init Code can perform push and pop
operations through the stack pointer SP. Listing 1 shows an example Init Code file that
demonstrates the setup of the SDRAM controller.
#include <defBF532.h>
.section program;
/********************************************************************/
[--SP] = ASTAT; // Save registers onto Stack
[--SP] = RETS;
[--SP] = (R7:0);
[--SP] = (P5:0);
/********************************************************************/
/*******Init Code Section********************************************/
/*******SDRAM Setup************/
Setup_SDRAM:
P0.L = lo(EBIU_SDRRC);
P0.H = hi(EBIU_SDRRC); // SDRAM Refresh Rate Control Register
R0 = 0x074A(Z);
W[P0] = R0;
SSYNC;
P0.L = lo(EBIU_SDBCTL);
P0.H = hi(EBIU_SDBCTL); // SDRAM Memory Bank Control Register
R0 = 0x0001(Z);
W[P0] = R0;
SSYNC;
P0.L = lo(EBIU_SDGCTL);
P0.H = hi(EBIU_SDGCTL); // SDRAM Memory Global Control Register
R0.H = 0x0091;
R0.L = 0x998D;
[P0] = R0;
SSYNC;
/********************************************************************/
(P5:0) = [SP++]; // Restore registers from Stack
(R7:0) = [SP++];
RETS = [SP++];
ASTAT = [SP++];
/********************************************************************/
RTS;
Listing 1. Example Init Code
Typically, an Init Code consists of a single section and is represented by a single block within the boot
stream. This block has, of course, the
INIT bit set. Nevertheless, an Init Block can also consist of multiple
sections. Then, multiple blocks represent the Init Code within the boot stream. Only the last block has the
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