Both, min_dB and max_dB, are floating type whereas the TLV is (always) unsigned.
The problem with the conversion of a negative floating-point number into an unsigned integer is, that the behavior is undefined. This may, depending on the platform, result in a wrong TLV, i.e. for the default values of min_dB (-51dB) and max_dB (0dB), alsactl generates the following state on an ARM cpu build with GCC:
control.1 { iface MIXER name Master value.0 255 value.1 255 comment { access 'read write user' type INTEGER count 2 range '0 - 255' tlv '00000001000000080000000000000014' dbmin 0 dbmax 5100 dbvalue.0 5100 dbvalue.1 5100 } }
With the fix applied, alsactl stores the correct TLV:
control.1 { iface MIXER name Master value.0 255 value.1 255 comment { access 'read write user' type INTEGER count 2 range '0 - 255' tlv '0000000100000008ffffec1400000014' dbmin -5100 dbmax 0 dbvalue.0 0 dbvalue.1 0 } }
Also tested for different combinations of min_dB and max_dB other than the default values.
Replaces: http://mailman.alsa-project.org/pipermail/alsa-devel/2016-May/107733.html
Fixes: http://mailman.alsa-project.org/pipermail/alsa-devel/2016-May/107628.html
Cc: Clemens Ladisch clemens@ladisch.de Signed-off-by: Jörg Krause joerg.krause@embedded.rocks --- src/pcm/pcm_softvol.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/src/pcm/pcm_softvol.c b/src/pcm/pcm_softvol.c index 802aa4b..061080d 100644 --- a/src/pcm/pcm_softvol.c +++ b/src/pcm/pcm_softvol.c @@ -658,8 +658,8 @@ static int add_tlv_info(snd_pcm_softvol_t *svol, snd_ctl_elem_info_t *cinfo) unsigned int tlv[4]; tlv[0] = SND_CTL_TLVT_DB_SCALE; tlv[1] = 2 * sizeof(int); - tlv[2] = svol->min_dB * 100; - tlv[3] = (svol->max_dB - svol->min_dB) * 100 / svol->max_val; + tlv[2] = (int)(svol->min_dB * 100); + tlv[3] = (int)((svol->max_dB - svol->min_dB) * 100 / svol->max_val); return snd_ctl_elem_tlv_write(svol->ctl, &cinfo->id, tlv); }