AD6620
bit set mode1 SRD1H | SRD2L | SRRFH | SRRFL;
/*—————————————————————————————*/
nop;
/*—————————————————————————————*/
spr1_asserted: /* SPORT1 Receive interrupt - do the fm demod and
increment the counter */
/* Insert code here to process I and Q data. The DSP serial port handler
has placed the samples in fm_demod_data and fm_demod_data+1 */
pop sts;
rti (db);
/* Pop the status stack */
push sts;
/* Push the status stack */
/* Use secondary set of DAGs and Register file */
/* Switch back to primary set of DAGs and Register file */
bit clr mode1 SRD1H | SRD2L | SRRFH | SRRFL;
nop;
bit set mode1 SRD1H | SRD1L | SRD2H | SRD2L | SRRFH |
SRRFL;
nop;
/* Insert code here for processing I and Q data pairs. The DSP serial
port handler has placed the samples in fm_demod_data through
fm_demod_data+3 */
.ENDSEG;
/*—————————————————————————————*/
Software for Diversity Channel Real Operation
The code for interfacing to Diversity Channel Real mode is very
similar to that of single channel. The only difference being the
number of channels allocated on the TDM chain. This process
can easily be extended for any number of TDM channels as
long as there is sufficient time in the frame to completely trans-
mit the data. This procedure works with the appended data as
well as serially cascaded devices. The code below demonstrates
setup and operation in diversity channel mode.
pop sts;
rti (db);
/* Pop the status stack */
/* Switch back to primary set of DAGs and Register file */
bit clr mode1 SRD1H | SRD1L | SRD2H | SRD2L | SRRFH |
SRRFL;
nop;
.ENDSEG;
/*—————————————————————————————*/
/*—————————————————————————————*/
.SEGMENT/DM dm_data;
/* multi-channel register setup */
TYPICAL LATENCY EXPECTATIONS
.VAR fm_demod_data[4];
sample from each channel */
/* Array for receiving 2 real and imag
In the AD6620 latency can be divided into three components.
For difficult filters, the largest component of latency is Algorith-
mic Latency. This type of latency is tied inseparably to the desired
filter response. For smaller or minimal filters, Fixed Latency begins
to dominate. This is the undesirable fixed delay associated with
the calculation of the output samples. Finally, Variable Latency,
is the smallest component. This is the delay that can be influenced
by the relative phase of internal decimated clocks with respect to
the SYNC_CIC.
.VAR fm_demod_tcb[8] = 0, 0, 0, 0, 0, 4, 1, fm_demod_data;
/* Transfer Control Block for reception of fm data */
/* —————————————————————————————*/
/*—————————————————————————————*/
setup_sport1:
r0 = 0;
dm(MTCS1) = r0;
/* multi-channel enable setup */
/* do not transmit on any channels */
Algorithmic Latency is a necessary component of any filtering
process be it analog or digital. Since frequency is a variation
with respect to time, it must take time to discriminate between
analog frequencies. Assuming the AD6620 is used to generate
linear phase, low-pass filters, the algorithmic latency is a direct
function of the number of RCF taps and the CIC decimation
ratios. In general, the largest part of the impulse response of
these filters is the center of the impulse response length, so that
the delay is represented by one-half the composite impulse
response length.
r0 = 0;
dm(MTCCS1) = r0;
dm(MRCCS1) = r0;
/* Compand Setup */
/* no companding on transmit */
/* no companding on receive */
r0 = 0x00100000;
dm(STCTL1) = r0;
/* Setup sport 1 transmit control register */
/* mfd = 1 */
r0 = 0x038c00f2;
dm(SRCTL1) = r0;
/* Setup sport 1 receive control register */
/* slen = 15, sden & schen enabled */
/* sign extend, external SCLK+RFS */
The impulse response length of the RCF is the number of taps
times the RCF input sample period. Therefore relative to the
input sample clock the impulse response length of the RCF is
given by;
r0 = fm_demod_tcb + 7; /* TCB address */
dm(fm_demod_tcb + 4) = r0; /* TCB point back to itself */
/* Kickoff DMA chain */
dm(CP1) = r0;
NTAPS − 1 × MCIC5 × MCIC2 + 1
(
)
rts (db)
/* RETURN */
/* enable sport1 receive interrupt */
/* Enable circular buffer 15 wrap
fADC
bit set imask SPR1I;
bit set imask CB15I;
interrupt for buffers full */
The impulse response length of the CIC5 is given by;
/*—————————————————————————————*/
/*—————————————————————————————*/
spr1_svc: jump spr1_asserted;
5 × MCIC5 − 5 × MCIC2 + 1
(
)
fADC
RTI;
RTI;
RTI;
REV. A
–40–
ADI [ ADI ]
