32.6.4 SAM L11 Secure Access Rights

Non-secure write to CTRL, EVCTRL, or NONSEC registers is prohibited.

Non-secure read to CTRL or EVCTRL registers will return zero with no error resulting.

Non-secure write to a bit of DIR, DIRCLR, DIRSET, DIRTGL, OUT, OUTCLR, OUTSET, or OUTTGL registers is prohibited if the corresponding bit in NONSEC is zero.

Non-secure write to a PINCFGn register or to a PMUXn register field, either directly or through a write to the WRCONFIG register, is prohibited if the corresponding bit in NONSEC is zero.

DIR, DIRCLR, DIRSET, DIRTGL, IN, OUT, OUTCLR, OUTSET, or OUTTGL bits, PINCFGn registers, or PMUXn register fields relating to secure I/O pins (i.e. the corresponding bits in NONSEC are zero), read as zero in non-secure mode, with no error resulting.

INTFLAG.NSCHK is set to 1 when NSCHK and NONSEC register values are different. Writing a 1 to INTFLAG.NSCHK will clear it and clear the PORT interrupt if enabled.

Secure code should initially write a 1 for all non-secure pins into both NONSEC and NSCHK registers. Then, whenever secure code writes a different value into NONSEC, INTFLAG.NSCHK will be set to 1 and a PORT interrupt will occur, if enabled. The non-secure code can then compare the values of the NONSEC and NSCHK registers to determine which PORT pins have just changed to secure or to non-secure. It should then copy the current NONSEC register value into NSCHK.