OPL4_REG_MIX_CONTROL_PCM
snd_opl4_write(opl4, OPL4_REG_MIX_CONTROL_PCM, 0xff);
id2 = snd_opl4_read(opl4, OPL4_REG_MIX_CONTROL_PCM);
snd_opl4_write(opl4, OPL4_REG_MIX_CONTROL_PCM, 0x3f);
.private_value = OPL4_REG_MIX_CONTROL_PCM