msrclr - 2024.2 English

Description

Copies the contents of the special purpose register MSR into register rD. Bit positions in the IMM value that are 1 are cleared in the MSR. Bit positions that are 0 in the IMM value are left untouched.

When MicroBlaze is configured to use an MMU (C_USE_MMU >= 1) this instruction is privileged for all IMM values except those only affecting C. This means that if the instruction is attempted in User Mode (MSR[UM] = 1) in this case a Privileged Instruction exception occurs.

Pseudocode

if MSR[UM] = 1 and IMM ≠ 0x4 then
   ESR[EC] ← 00111
else
   (rD)  ← (MSR)
   (MSR) ← (MSR) ˄ (IMM))

Registers Altered

• rD
• MSR
• ESR[EC], in case a privileged instruction exception is generated

Latency

• 1 cycle

Notes

• MSRCLR will affect the Carry bit immediately while the remaining bits will take effect one cycle after the instruction has been executed. When clearing the IE bit, it is guaranteed that the processor will not react to any interrupt for the subsequent instructions.
• The value read from MSR might not include effects of the immediately preceding instruction (dependent on pipeline stall behavior). An instruction that does not affect MSR must precede the MSRCLR instruction to guarantee correct MSR value. This applies to both the value copied to register rD and the changed MSR value itself.
• The immediate values has to be less than 215 when C_USE_MMU >= 1 (User Mode), and less than 214 otherwise. Only bits 17 to 31 of the MSR can be cleared when C_USE_MMU >= 1 (User Mode), and.bits 18 to 31 otherwise.
• This instruction is only available when the parameter C_USE_MSR_INSTR is set to 1.
• When clearing MSR[VM] the instruction must always be followed by a synchronizing branch instruction, for example BRI 4.