IBM PC Mouse

/* PS/2 Mouse Synopsis
 * http://www.computer-engineering.org/ps2mouse/
 *
 * Command:
 * 0xFF: Reset
 * 0xF6: Set Defaults Sampling; rate=100, resolution=4cnt/mm, scaling=1:1, reporting=disabled
 * 0xF5: Disable Data Reporting
 * 0xF4: Enable Data Reporting
 * 0xF3: Set Sample Rate
 * 0xF2: Get Device ID
 * 0xF0: Set Remote Mode
 * 0xEB: Read Data
 * 0xEA: Set Stream Mode
 * 0xE9: Status Request
 * 0xE8: Set Resolution
 * 0xE7: Set Scaling 2:1
 * 0xE6: Set Scaling 1:1
 *
 * Mode:
 * Stream Mode: devices sends the data when it changs its state
 * Remote Mode: host polls the data periodically
 *
 * This code uses Remote Mode and polls the data with Read Data(0xEB).
 *
 * Data format:
 * byte|7       6       5       4       3       2       1       0
 * ----+--------------------------------------------------------------
 *    0|Yovflw  Xovflw  Ysign   Xsign   1       Middle  Right   Left
 *    1|                    X movement
 *    2|                    Y movement
 */