Variable-Length Encoding (VLE) register rules

[Bloodhound]

Hi All,

I've been working on a VLE project (written in asm) and I am running in to an annoying issue with certain registers not able to perform tasks.

For example, a simple compare command...

se_cmp  r29,r26  << That is ok

se_cmp  r29,r10  << That creates an error 'Invalid register specified".

I have the VLE reference manual but I cannot find where it discusses what combination of registers are valid to use in situations like this.

Does anyone have any pointers?

Thanks.

[Bloodhound]

Ok thanks Lukas.

[lukaszadrapa]

Hi,

copied from http://www.freescale.com/files/32bit/doc/ref_manual/VLEPEM.pdf , page 23:

"VLE instructions use GPRs and SPRs with the following limitations:

• Most VLE instructions using 16-bit formats are limited to addressing GPR0–GPR7 and

GPR24–GPR31. Move instructions are provided to transfer register contents between these

registers and GPR8–GPR23.

• VLE compare and bit test instructions using the 16-bit formats implicitly set their results in CR0."

That's because there are only 4 bits to specify a GPR in VLE instruction.

Regards,

Lukas