of Microprocessors

686 MUSICAL ApPLICATIONS OF MICROPROCESSORS
TIME
COUNT ~ a
?
NO
Fig. 18-20. Level 2 general-control routine
This argument specifies how many milliseconds of sound to generate before
returning. Although no new events can be started during this interval, any
number may terminate (as mentioned earlier, events are defined by their
starting time and duration). New events can only be created by the NO­
TRAN interpreter when it is in control.
The first task is to scan the memory area devoted to event control
blocks. Every active block found is further tested for the event type and the
corresponding Level 2 generator routine is called. After a complete scan
through all of the blocks, 30 samples have been added to the sample buffer
and the buffer address pointers in all sound control blocks have been incremented
by 30.
The next task is to determine if the large sample buffer is full. In the
original implementation of NOTRAN, this buffer was 3,000 samples long,
which would therefore hold 100 of the small sample blocks. If the large
buffer is full, then a sample record would be written to the mass storage
device. Following this, all of the sound control blocks would be scanned and
their sample buffer addresses reset to the beginning of the large sample
buffer. While this method of handling (he sample buffer seems redundant
(the buffer address field of all sound control blocks is the same), keeping the