Hi,
I am fairly new to ARM processor and start work with cortexA57 recently. After reading the technical manual and programmer guide , I have some questions regarding the exception level of v8.
1. How does the exception level change from one to another ？
According to the documents, the EL can only be changed on taking exception. And also when an exception happens, the EL can only changed to a higher level. Then , how is it changed from higher EL to lower EL ? For example, on reset, the processor starts at EL3, then how does it switch to execute program on the other levels ? Could anyone give an example to show how the EL changes during a boot sequence ?
2. How to get the current EL value ?
The document says the register PSTATE contains a field CurrentEL which indicates on which EL the processor is executing. Is the PSTATE register only existed in Aarch64 execution state , or it is also existed in Aarch32 ? If not, how to read current EL value from Aarch32 ?
Thanks in advance !
Best regards,
Xinwei