If you would like to run a particular function (eg. MyFunction_SRAM()) from PSRAM to enhance the code execution speed. You can make some changes in both startup file (eg. startup_XMC4500.s) and linker descript file (*.ld):
1) Define a new section in *.ld before "/*Heap - Bank1*/"
/*=== SRAMCode section for PSRAM code ============*/
SRAMCodeLoad = eROData + __Xmc4500_Data_Size;
SRAMCode_Section : AT (SRAMCodeLoad)
{
SRAMCodeStart = ABSOLUTE(.);
* (.SRAMCode);
. = ALIGN(4);
SRAMCodeEnd = ABSOLUTE(.);
} > PSRAM_1
SRAMCodeSize = SRAMCodeEnd - SRAMCodeStart;
2) Add a copy process in startup_XMC4500.s before "SKIPSRAMCODECOPY:"
/*========== SRAM code copy ===========================*/
SKIPDATACOPY:
/* R0 = Start address, R1 = Destination address, R2 = Size */
LDR R0, =SRAMCodeLoad
LDR R1, =SRAMCodeStart
LDR R2, =SRAMCodeSize
/* Is there anything to be copied? */
CMP R2,#0
BEQ SKIPSRAMCODECOPY
/* For bytecount less than 4, at least 1 word must be copied */
CMP R2,#4
BCS STARTSRAMCODECOPY
/* Byte count < 4 ; so bump it up */
MOV R2,#4
STARTSRAMCODECOPY:
/*
R2 contains byte count. Change it to word count. It is ensured in the
linker script that the length is always word aligned.
*/
LSR R2,R2,#2 /* Divide by 4 to obtain word count */
/* The proverbial loop from the schooldays */
SRAMCODECOPYLOOP:
LDR R3,[R0]
STR R3,[R1]
SUBS R2,#1
BEQ SKIPSRAMCODECOPY
ADD R0,#4
ADD R1,#4
B SRAMCODECOPYLOOP
/*=================== end of Copy process =================*/
3) Declare function in program
void MyFunction_SRAM (void) __attribute__ ((section (".SRAMCode")));With these, the function MyFunction_SRAM will be located in section SRAMCode. It will be copied to PSRAM in startup code and then run from PSRAM.
