Q: what does the $PMTKPMC sentence mean?
The $PMTKPMC sentence is output regularly while GPS receivers based on MediaTek MT3339 chip are set to a power periodic mode ($PMTK225 = PMTK_CMD_PERIODIC_MODE) different than 0 (= normal operation).
Example:
$PMTKPMC,0001212140,1,0000000000,0000011960,0000012000,0000000000,0000000000,3,0,0,044*4B
...
$PMTKPMC,0001213140,1,0000000000,0000010960,0000012000,0000000000,0000000000,3,0,0,044*4B
...
$PMTKPMC,0001214150,1,0000000000,0000009950,0000012000,0000000000,0000000000,3,0,0,044*46
...
$PMTKPMC,0001215140,1,0000000000,0000008960,0000012000,0000000000,0000000000,3,0,0,044*44
...
$PMTKPMC,0001216160,1,0000000000,0000007940,0000012000,0000000000,0000000000,3,0,0,044*48
...
This sentence is currently not documented by MediaTek and shall be disregarded.