USAD8{cond} {Rd}, Rn, Rm

USADA8{cond} Rd, Rn, Rm, Ra

where:

The USAD8 instruction finds the four differences between the unsigned values in corresponding bytes of Rn and Rm. It adds the absolute values of the four differences, and saves the result to Rd.

The USADA8 instruction adds the absolute values of the four differences to the value in Ra, and saves the result to Rd.

You cannot use PC for any register.

You can use SP in ARM instructions but these are deprecated in ARMv6T2 and above. You cannot use SP in Thumb instructions.

These instructions do not alter any flags.

These ARM instructions are available in ARMv6 and above.

These 32-bit Thumb instructions are available in ARMv6T2 and above. For the ARMv7-M architecture, they are only available in an ARMv7E-M implementation.

There are no 16-bit Thumb versions of these instructions.

    USAD8       r2, r4, r6
    USADA8      r0, r3, r5, r2
    USADA8VS    r0, r4, r0, r1

    USADA8      r2, r4, r6      ; USADA8 requires four registers
    USADA16     r0, r4, r0, r1  ; no such instruction