We are running a survey to help us improve the experience for all of our members. If you see the survey appear, please take the time to tell us about your experience if you can.
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
Ash, Thanks a lot for your explanation !