I’m using GCC on a Cortex-M4F (LPC43xx family). I need more than the 3 configurable MPU regions for this port. I decided to do away with the privileged flash area because I don’t need it (privileged background map is enabled and my unprivileged flash area does not reach there, so privileged accesses are enabled by default and unprivleged accesses are blocked). What I did:

• added the fourth area to all my task parameters (all tasks are created using xTaskCreateRestricted);
• took out the lines setting portMPUREGIONBASEADDRESSREG and portMPUREGIONATTRIBUTE_REG for the privileged flash area in prvSetupMPU (mpu/port.c);
• changed a few lines at the start of mpu/portmacro.h from ~~~

define portUNPRIVILEGEDFLASHREGION ( 0UL )

define portPRIVILEGEDFLASHREGION ( 1UL )

define portPRIVILEGEDRAMREGION ( 2UL )

define portGENERALPERIPHERALSREGION ( 3UL )

define portSTACK_REGION ( 4UL )

define portFIRSTCONFIGURABLEREGION ( 5UL )

define portLASTCONFIGURABLEREGION ( 7UL )

~~~ to ~~~

define portUNPRIVILEGEDFLASHREGION ( 0UL )

define portPRIVILEGEDRAMREGION ( 1UL )

define portGENERALPERIPHERALSREGION ( 2UL )

define portSTACK_REGION ( 3UL )

define portFIRSTCONFIGURABLEREGION ( 4UL )

define portLASTCONFIGURABLEREGION ( 7UL )

~~~ What did not work: the fourth area is never set (whatever region I put there does not get activated). I checked portNUMCONFIGURABLEREGIONS, it’s obviously 4 instead of 3 now. I looked at the FreeRTOS code and the fourth region should be working, I have no idea why it’s not. I appreciate any help.

Never mind, I found it… xPortPendSVHandler in mpu/port.c only swaps in 4 regions at most (including the stack region), so I added a few lines that fixed it. If anyone has the same problem, delete line 495 and add this in its place (assuming you defined the appropriate symbol): ~~~

if !defined(FREERTOSEXTRAMPU_REGION)

    "   stmia r2!, {r4-r11}                 n" // original line

else

    "   stmia r2, {r4-r11}                  n" // don't update r2
    "   ldmia r1!, {r4-r5}                  n" // load 1 set of MPU regs
    "   stmia r2, {r4-r5}                   n" // write 1 set of MPU regs

endif

~~~