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AR# 47558

Zynq-7000 AP SoC, APU - Unallocated Memory Hint Instruction can Generate an Undefined Exception Instead of Being Treated as A NOP

Description

The Unallocated Memory Hint instruction should execute as a NOP, but the CPU generates an UNDEF exception when bits [15:12] of the instruction encoding are not 0x0F. In practice, this issue is not expected to be significant because such instruction encodings are not to be generated by the compiler, nor used in handcrafted programs.

The work-arounds consist of modifying the instruction encoding so bits [15:12] = 0x0F or make the exception handler emulate the expected behavior of the instruction (i.e., NOP) before returning to normal program execution.

Solution

Impact:

Minor. Work-arounds are used by compilers and handcrafted programs.

Work-around:

Modify the hint instruction encoding so bits [15:12] = 0x0F or make the exception handler emulate the expected behavior of the instruction (i.e., NOP) before returning to normal program execution.

Configurations Affected:

Systems that use one or both ARM processors.

Device Revision(s) Affected: All, no plan to fix. Refer to (Xilinx Answer 47916) - Zynq-7000 Design Advisory Master Answer Record



Modify the hint instruction encoding so bits [15:12] = 0x0F or make the exception handler emulate the expected behavior of the instruction (i.e., NOP) before returning to normal program execution.

AR# 47558
Date Created 05/30/2012
Last Updated 09/06/2012
Status Active
Type Design Advisory
Devices
  • Zynq-7000