SETSYSP mn
Return From User Interrupt
Rabbit 4000 Instruction
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ED B1 n m
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SETSYSP mn
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12 (2,2,2,2,2,2)
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SU={SU[1:0],SU[7:2]}
tmplow = (SP)
tmphigh = (SP + 1)
SP = SP + 2
if {tmp != mn}
System Violation
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Description
This instruction is used to handle user mode interrupts in system/user mode. It sets the current processor
mode to the previous processor mode by rotating two places to the right the bits of SU. Bits 1 and 0 are
moved to bit positions 7 and 6 respectively. The System/User Mode Register, SU, is an 8-bit register that
forms a stack of the current processor mode and the previous 3 modes.
This is a chained-atomic instruction, meaning that an interrupt cannot take place between this instruction
and the instruction following it.