On 20 September 2013 06:55, Mj Embd mj.embd@gmail.com wrote:
Hello Andre, I need a bit clarification here, if you read the next line after the line you have quoted. It clearly says that you can use a MCR to change from Secure to NS in Monitor Mode
No, it's not saying that, because Monitor mode is always Secure: this is exactly why an MCR to change SCR.NS is OK only in Monitor mode -- it doesn't change from Secure to Non-Secure. Only when you do an exception-return to leave Monitor mode will you drop into the NonSecure world.
"Use an MCR instruction that writes SCR.NS to change from Secure to Non-secure state. This means ARM recommends that software does not alter SCR.NS in any mode except Monitor mode. ARM deprecates changing SCR.NS in any other mode."
The text says "don't change from Secure to NonSecure by flipping SCR.NS". It then lays out the corollary: the only time you then can change SCR.NS is when it won't switch from Secure to NonSecure, which is when you're in Monitor mode.
-- PMM