I have a quastion regarding reading TBR registers on p2020 e500v2 CPU.
I wrote the following asm instructions:
mftbu r5 /* Read upper Time Base */ mftb r6 /* Read lower Time Base */ mftbu r7 /* Read upper Time Base again */
When i comliped (using GNU 4.3.3) and viewed the asm instruction I saw that mftbu and mftb were replaced with mfspr instruction.
after search in documentation i found in:EREF 2.0: A Programmer’s Reference Manual for Freescale Power Arch Processors (P.504). The following note : mftb was part of the original PowerPc arch, but is being phased out of PowerISA....
How did the GNU compilar knew that it should replace the obsolete instruction ? did NXP added a patch to the GNU release ? should i worry that the compilar can change explicitly written asm instructions ?