Hi everyone ,
I'm currently using a Cortex-A9 processor (NXP Freescale i.MX6S).
My project is to develop a simple OS, but I met a problem:
When I am trying to control some peripherals (such as UART and GPIO) directly under ARM USER MODE, the program stopped and jumped into some other exceptional handlers.
However, if I control these peripherals under ARM SYSTEM MODE, everything is fine.
I know that there are 7 ARM modes, USER mode is the non-privilege mode and the others are privilege modes. USER mode is redistricted in accessing some resources, but I didn't find out any document explain these restrictions explicitly.
Could you give me some advises? Very Appreciate it !!!