STM r0!, {}
I have looked at Thumb2 instruction set web but I can't find the behaviour of STM command if the reglist is empty.
Thanks in advance.
Just noticed you are talking about the M0 which has the ARMv6-M instruction set not ARMv7-M. It excludes most of the 32 bit Thumb-2 instructions including the T2 form of LDMIA.