Xilinx MicroBlaze Reference Manual page 51

exception handler performs the actual procedure call to the system-service routine on
behalf of the application program.
The execution environment expected by the system-service routine requires the execution
of prologue instructions to set up that environment. Those instructions usually create the
block of storage that holds procedural information (the activation record), update and
initialize pointers, and save volatile registers (registers the system-service routine uses).
Prologue code can be inserted by the linker when creating an executable module, or it can
be included as stub code in either the system-call interrupt handler or the system-library
routines.
Returns from the system-service routine reverse the process described above. Epilog code
is executed to unwind and deallocate the activation record, restore pointers, and restore
volatile registers. The interrupt handler executes a return from exception instruction (RTED)
to return to the application.
MicroBlaze Processor Reference Guide
UG984 (v2016.2) June 8, 2016
UG984 (v2016.1) April 6, 2016
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Chapter 2: MicroBlaze Architecture
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