static bool cmd_set_features(IDEState *s, uint8_t cmd)
{
    uint16_t *identify_data;

    if (!s->bs) {
        ide_abort_command(s);
        return true;
    }

    /* XXX: valid for CDROM ? */
    switch (s->feature) {
    case 0x02: /* write cache enable */
        bdrv_set_enable_write_cache(s->bs, true);
        identify_data = (uint16_t *)s->identify_data;
        put_le16(identify_data + 85, (1 << 14) | (1 << 5) | 1);
        return true;
    case 0x82: /* write cache disable */
        bdrv_set_enable_write_cache(s->bs, false);
        identify_data = (uint16_t *)s->identify_data;
        put_le16(identify_data + 85, (1 << 14) | 1);
        ide_flush_cache(s);
        return false;
    case 0xcc: /* reverting to power-on defaults enable */
    case 0x66: /* reverting to power-on defaults disable */
    case 0xaa: /* read look-ahead enable */
    case 0x55: /* read look-ahead disable */
    case 0x05: /* set advanced power management mode */
    case 0x85: /* disable advanced power management mode */
    case 0x69: /* NOP */
    case 0x67: /* NOP */
    case 0x96: /* NOP */
    case 0x9a: /* NOP */
    case 0x42: /* enable Automatic Acoustic Mode */
    case 0xc2: /* disable Automatic Acoustic Mode */
        return true;
    case 0x03: /* set transfer mode */
        {
            uint8_t val = s->nsector & 0x07;
            identify_data = (uint16_t *)s->identify_data;

            switch (s->nsector >> 3) {
            case 0x00: /* pio default */
            case 0x01: /* pio mode */
                put_le16(identify_data + 62, 0x07);
                put_le16(identify_data + 63, 0x07);
                put_le16(identify_data + 88, 0x3f);
                break;
            case 0x02: /* sigle word dma mode*/
                put_le16(identify_data + 62, 0x07 | (1 << (val + 8)));
                put_le16(identify_data + 63, 0x07);
                put_le16(identify_data + 88, 0x3f);
                break;
            case 0x04: /* mdma mode */
                put_le16(identify_data + 62, 0x07);
                put_le16(identify_data + 63, 0x07 | (1 << (val + 8)));
                put_le16(identify_data + 88, 0x3f);
                break;
            case 0x08: /* udma mode */
                put_le16(identify_data + 62, 0x07);
                put_le16(identify_data + 63, 0x07);
                put_le16(identify_data + 88, 0x3f | (1 << (val + 8)));
                break;
            default:
                goto abort_cmd;
            }
            return true;
        }
    }

abort_cmd:
    ide_abort_command(s);
    return true;
}
Unknown