RM48L950: Undef exception after MPU initialization and coprocessor access

Westin Sykes

Part Number: RM48L950

I am experimenting with using the MPU, and I found that after initializing it and switching to user mode, I get an undef entry exception at this instruction: "FMXR FPEXC, R1". I understand coprocessors can be configured to not work in user mode and this will cause an undef exception, but I have found 0xF00000 which indicates to me that if the coprocessor was accessible in system mode it would also be accessible in user mode. What else can cause this exception?

Thanks

over 7 years ago

0 Westin Sykes over 7 years ago

Expert 1315 points

I have more information that may be useful. I have found that when changing to user mode, most of the VFP_SYSTEM registers significantly change. Is this expected?

0 QJ Wang over 7 years ago in reply to Westin Sykes

TI__Guru**** 196346 points

Hello,

The VFP system registers can only be accessed in Privileged modes.

The above table shows that a Privileged mode is sometimes required to access a VFP system register. When a Privileged mode is required, an instruction that attempts to access a register in a nonprivileged mode takes the Undefined Instruction exception.

0 Westin Sykes over 7 years ago in reply to QJ Wang

Expert 1315 points

Where can that table be found?

0 Sunil Oak over 7 years ago in reply to Westin Sykes

TI__Mastermind 49120 points

It is on page 345 of the CPU's technical reference manual (version r1p3), in the section that describes the registers inside the FPU.

Regards,
Sunil

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RM48L950: Undef exception after MPU initialization and coprocessor access