[FAQ] MCU-PLUS-SDK-AM243X: Use SBL's memory from application

Hi,

You can use the SBL memory in primary R5's application by allocating it to a uninitialized sections (NOLOAD) section.

Steps to do that -

1. Define MSRAM_SBL section in Primary R5Fs app

/* SBL used memory, use only for uninitalized sections */
MSRAM_SBL : ORIGIN = 0x70000000 , LENGTH = 0x60000

2.  Allocate uninitialized/NOLOAD sections like .bss, .stack to this newly created section 

/* This is rest of uninitialized data. This can be placed in DDR if DDR is available and needed */
GROUP {
.bss: {} palign(8) /* This is where uninitialized globals go */
RUN_START(__BSS_START)
RUN_END(__BSS_END)
.sysmem: {} palign(8) /* This is where the malloc heap goes */
.stack: {} palign(8) /* This is where the main() stack goes */
} > MSRAM_SBL

3. Confirm from the memory map file, the allocation of uninitialized sections. Check the UNINITILIAZED section attribute at the beginning. 

.bss       0    70000000    00001498     UNINITIALIZED
                  70000000    00001008     (.common:gHwiCtrl)
                  70001008    00000280     ti_drivers_config.o (.bss.gUartObjects)
                  70001288    00000120     libsysbm.a : trgmsg.c.obj (.bss:_CIOBUF_)
                  700013a8    000000a0     (.common:__TI_tmpnams)
                  70001448    00000038     (.common:gClockCtrl)
                  70001480    00000008     (.common:parmbuf)
                  70001488    00000004     nortos.am243x.r5f.ti-arm-clang.debug.lib : HwiP_armv7r_vim.obj (.bss.gdummy)
                  7000148c    00000004     libc.a : memory.c.obj (.bss.sys_free)
                  70001490    00000004     (.common:gUartHandle)
                  70001494    00000004     --HOLE--

.sysmem    0    70001498    00008000     UNINITIALIZED
                  70001498    00000010     libc.a : memory.c.obj (.sysmem)
                  700014a8    00007ff0     --HOLE--

.stack     0    70009498    00004000     UNINITIALIZED
                  70009498    00000004     nortos.am243x.r5f.ti-arm-clang.debug.lib : boot_armv7r_asm.obj (.stack)
                  7000949c    00003ffc     --HOLE--

Some points to note:

• Strictly allocate the SBL memory for the NOLOAD or uninitialized sections on primary R5
  • This memory can be only used by primary R5 which runs the bootloader/SBL. If memory is allocated to other R5 cores, as they can start executing before SBL is fully done, they may overwrite SBL's content causing boot failure

Hope this helps!

Regards,

Prasad