Kinetis K53 write to SIM_SOPT1CFG causes bus fault

[kfranz]

I am trying to modify SIM_SOPT1CFG.

Either line of 'C' code causes a bus fault:

SIM_SOPT1CFG |= (SIM_SOPT1CFG_URWE_MASK);

or

*(unsigned long *)0x40047004 |= (0x1000000u);

When at either line of code above I can use a JTAG debugger and manually set the bit. So, I know the register can be accessed via the JTAG debugger when at that line of code.

What am I missing? Why can't I do this?

[bobpaddock]

Is there any clocks that need turned on to access this register?
The debugger could have different clocking systems going on.

Also do you really need to read the register with '|='?
NXP frequently shows these in examples where only simple assignment '=' should be used.

[Julián_AragónM]

Hi @bobpaddock,

The '|=' operators are a simple way to access a register without overwriting it, this way, the configuration you add will be additional and will not affect any other bits.

Best regards, Julian

[bobpaddock]

The |= is a Read-Modify-Write operation that at best wastes time when
used, where an assignment is appropriate.

At its worst using |= can unintentionally clear unexpected bits,
causing interrupts to be lost, when assignment was the intention on
status registers that have Write-1-To-Clear (W1C) bits.

It is simply bad practice to use |= when it is not needed.

Sadly the NXP documentation and example code is full of this bad
practice, and it harms people new to Embedded System development by
setting a bad precedent of coding style.

[Julián_AragónM · Accepted solution]

Hi @kfranz,

please try it this way instead;

SIM->SOPT1CFG |= SIM_SOPT1CFG_URWE_MASK;

 As this is the way you can access the register now. Hope it helps!

Best regards, Julian