Circular Buffer Pointer Logic

Implement circular buffer pointer manipulation logic in ARM assembly for a high-throughput DMA-based UART receiver. The routine must update read and write pointers in a ring buffer while preventing overflow and underflow.

Constraints

• r0 = base address of buffer (not used directly).
• r1 = write pointer, r2 = read pointer, r3 = buffer size.
• r4 = operation flag (0 = write, 1 = read).
• On write: increment write pointer; if equals size, wrap to 0.
• On overflow (write pointer catches read pointer), return error code -1.
• On read: increment read pointer; if equals size, wrap to 0.
• On underflow (read equals write), return error code -2.
• Updated pointer returned in r0.
• Must preserve r5-r7.