Checksum Over Flash Region

Compute a 32-bit additive checksum over a flash region in assembly, processing four bytes at a time and handling a non-multiple-of-four length.

Constraints

• r0 = start address, r1 = length in bytes, result in r0.
• Sum 32-bit words while at least 4 bytes remain.
• Sum any trailing bytes individually.
• Wrapping addition is intended, not an error.
• A length of 0 returns 0.
• No calls to C.