Mixer Chip Programming
4-3
Certain bits in a mixer register may be reserved, in which case their values are
undefined. When these bits are accessed, you must treat them as fully undefined.
This is essential for software compatibility with future mixer chips. Follow the
guidelines below:
1.
Do not depend on the values of any undefined bits when testing the value
of defined register bits. Mask them out when testing.
2.
Do not depend on the values of any undefined bits when storing them to
memory or another register.
3.
Do not depend on any reserved bits' ability to retain information.
4.
When writing to a mixer register, you should always read back the current
value of the register and only alter the bit settings which you wish to
change.
5.
When writing to a mixer register, always set the reserved bit to zero.
As a rule of thumb when controlling a mixer register, you should always query the
current settings before changing them and restore their original settings as soon as
you have finished using it.
