- /*
- * We encode the previous and the current state using a byte.
- * The previous state in the MSB nibble, the current state in the LSB
- * nibble. Then use a table to decide the direction of the turn.
- */
- sum = (encoder->last_stable << 4) + state;
- switch (sum) {
- case 0x31:
- case 0x10:
- case 0x02:
- case 0x23:
- encoder->dir = 0; /* clockwise */
- break;
-
- case 0x13:
- case 0x01:
- case 0x20:
- case 0x32:
- encoder->dir = 1; /* counter-clockwise */
- break;
-
- default:
- /*
- * Ignore all other values. This covers the case when the
- * state didn't change (a spurious interrupt) and the
- * cases where the state changed by two steps, making it
- * impossible to tell the direction.
- *
- * In either case, don't report any event and save the
- * state for later.
- */