Xilinx MicroBlaze Reference Manual page 258

rtid
Return from Interrupt
rn from Interrupt
rtid rA, IMM
1 0 1 1 0 1 1 0 0 0 1
0 6
Description
Return from interrupt will branch to the location specified by the contents of rA plus the IMM field,
sign-extended to 32 bits. It will also enable interrupts after execution.
This instruction always has a delay slot. The instruction following the RTID is always executed before
the branch target. That delay slot instruction has interrupts disabled.
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.
With low-latency interrupt mode (C_USE_INTERRUPT = 2), the Interrupt_Ack output port is set to 10
when this instruction is executed, and subsequently to 11 when the MSR{IE] bit is set.
Pseudocode
if MSR[UM] = 1 then
←
ESR[EC]
else
←
(rA) + sext(IMM)
PC
Interrupt_Ack
allow following instruction to complete execution
←
MSR[IE]
←
MSR[UM]
←
MSR[VM]
Interrupt_Ack
Registers Altered
• PC
• MSR[IE], MSR[UM], MSR[VM]
• ESR[EC], in case a privileged instruction exception is generated
Latency
• 2 cycles
Note
Convention is to use general purpose register r14 as rA.
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.
MicroBlaze Processor Reference Guide
UG984 (v2016.2) June 8, 2016
UG984 (v2016.1) April 6, 2016
rA
11
00111
←
10
1
MSR[UMS]
MSR[VMS]
←
11
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Chapter 5: MicroBlaze Instruction Set Architecture
IMM
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258
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