MicroBlaze Processor Reference Guide 278
UG984 (v2018.2) June 21, 2018 www.xilinx.com
Chapter 5: MicroBlaze Instruction Set Architecture
rted
Return from Exception
rted
rA, IMM
1 0 1 1 0 1 1 0 1 0 0 rA IMM
0 6 11 16
31
Description
Return from exception will branch to the location specified by the contents of rA plus the IMM field,
sign-extended to 32 bits. The instruction will also enable exceptions after execution.
This instruction always has a delay slot. The instruction following the RTED is always executed before
the branch target.
When MicroBlaze is configured to use an MMU (C_USE_MMU >= 1) this instruction is privileged. This
means that if the instruction is attempted in User Mode (MSR[UM] = 1) a Privileged Instruction
exception occurs.
Pseudocode
if MSR[UM] = 1 then
ESR[EC] ← 00111
else
PC
← (rA) + sext(IMM)
allow following instruction to complete execution
MSR[EE] ← 1
MSR[EIP]
← 0
MSR[UM] ← MSR[UMS]
MSR[VM] ← MSR[VMS]
ESR
← 0
Registers Altered
•PC
• MSR[EE], MSR[EIP], MSR[UM], MSR[VM]
•ESR
Latency
• 2 cycles
Notes
Convention is to use general purpose register r17 as rA. This instruction requires that one or more of
the MicroBlaze parameters C_*_EXCEPTION are set to 1 or that C_USE_MMU > 0.
A delay slot must not be used by the following: imm, branch, or break instructions. Interrupts and
external hardware breaks are deferred until after the delay slot branch has been completed.
The instruction should normally not be used when MSR[EE] is set, since if the instruction in the delay
slot would cause an exception, the exception handler would be entered with exceptions enabled.
Code returning from an exception must first check if MSR[DS] is set, and in that case return to the
address in BTR.
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