We begin our description with
the·
programming
~equence
required to initiate a sound
in
the CGP.
In
the Kurzweil 250,. only 12
channels of the possible 16 channels are provided. Each channel has
an
on/off hardware control located in the Channel Enable Word
(CEW). This bit must be off
(0)
befQre
channel initialization begins.
Then, we write the
CSW with all
Os
which performs the following
functions:
1. Initializes the FIFO write and read pointers to FIFO location
O.
2. Sets the "FIFOFUL" bit
to
0,
indicating that the FIFO
is
not
full, and should be filled the first time the channel is
polled.
3.
Clears the "End-of-Waveform Pending" and "Audio Enable"
bits (described later).
4. Sets the "Toggle" bit
to
point to the lower span.
Once the CSW
is
initialized, it should not be re-written until
the channel has been de-allocated, because the parameters are
modified as the sound progresses.
Next, two spans
should
be
loaded into the appropriate locations
of the CGP, the lower one being first, followed by the higher one.
Note that the span has a maximum
length of 64K samples, and
may
never cross a 64K boundary. When the appropriate sampling and
alias clocks and amplitude DAC have been initialized, the channel
can
be
enabled
by
writing
to
the
CEW.
First, we will describe a typical life of a waveform.
We
begin
with setting up
all of parameters described above. When all
is
ready, the channel
in
question is enabled by writing to the
appropriate bit
in
the Channel Enable Word.
On
the subsequent 16
polls
of
the enabled channel, the CGP will perform a DMA cycle
to
fetch a sound sample pOinted to by the DMA HIGH and DMA LOW
parameters
in
the CGP parameter memory. This DMA address is then
incremented and written back into the CGP
local memory, compared
with the DMA
LAST. The sound sample
is
also written into the
CGP
local memory
in
a special location dedicated to this channel's FIFO.
The pointer address to the channel's
CGP
FIFO pointed
to
by
a field
in
the CHANNEL STATUS WORD (CSW). This word
is
updated every time
the
FIFO
is
written to or read from. The CSW is written into only
once, when the channel
is
being initialized.
Kurzwell 250 Service Manual, Chapter 3
3-
1 8
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