Filter
Top Products
Architecture
20
2.6 Memory Management Unit (MMU)
2.6.1 R3900 Processor Core operating modes
The R3900 Processor Core has two operating modes, user mode and kernel mode. Normally the
processor operates in user mode. It switches to kernel mode if an exception is detected. Once in
kernel mode, it remains there until an RFE (Restore From Exception) instruction is executed.
(1) User mode
User mode makes available one of the two 2 Gbyte virtual address spaces (kuseg). In this
mode the most significant bit of each kuseg address in the memory map is 0. Attempting to
access an address whose MSB is 1 while in user mode returns an Address Error exception.
(2) Kernel mode
Kernel mode makes available a second 2 Gbyte virtual address space (kseg), in addition to the
kuseg accessible in user mode. The MSB of each kseg address in the memory map is 1.