ANALOG DEVICES ADSP2106x Service Manual

Engineer To Engineer Note EE-109

Technical Notes on using Analog Devices’ DSP components and development tools

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ADSP-2106x: Using the SPORTs
as additional timers

March 23, 2000 (bk)

The ADSP-21060/2/1 devices feature a single
timer. One timer might be enough for most of
typical signal processing applications, but even
not for all of them. If additional timers are
required, unused SPORT channels can be used
to realize them.

How does it work?

The SHARC features two serial port devices.
Since the transmit and receive units of both of
the ports have separate and independent bit rate
generators and interrupt logic, up to four
additional timers can be realized.

Two 16-Bit registers, xCLKDIV and xFSDIV
control the timer period. The following equation
is used to calculate the interrupt rate ir:

=

ir

( ) ( )

Please note, xFSDIV shouldn’t be less than
SLEN which controls the serial word length
(=SLEN+1) from 3 up to 32 bits. If f
50MHz the maximum timer period without
DMA operation is around 85 seconds.

The following example code demonstrates the
initialization of the receive channel of SPORT1:

setup_rx1:
/* global interrupt enable */

bit set MODE1 IRPTEN;

fCLKIN

xFSDIVxCLKDIV

11 +⋅+

CLKIN

is

/* enable SPORT1 receive interrupt
*/
bit set IMASK SPR1I;

/* 0x2000 cycles */
r0 = 0x1FFF0000;
dm(RDIV1) = r0;

/* enable, 4 bit, RFS and RCLK
internal, early RFS */
r0 = 0x00006431;
dm(SRCTL1) = r0;

Initialization of RX1 for timer operation

The initialization sequence for the transmit
channel differs only by the bit DITFS for data
independent transmission:

setup_tx1:
/* global interrupt enable */

bit set MODE1 IRPTEN;
/* enable transmit interrupt */

bit set IMASK SPR1I;
/* 0x2000 cycles */

r0 = 0x1FFF0000;
dm(TDIV1) = r0;

/* enable, 4 bit, RFS and RCLK
internal, early RFS */
r0 = 0x0000E431; /* DITFS = 1 */
dm(STCTL1) = r0;

Initialization of TX1 for timer operation

Of course, the serial ports have been designed
for inter-chip communication. Once enabled, the
SPORTs will activate the dedicated pins. To
avoid the need of external glue the SPORTs
should be programmed for fully internal
operation. Then, all the pins except Rx work as
output. Rx has an internal pull-up of 50Ω and

can be left open, too. The frame sync signals
indicate a timer overrun. The bit LxFS controls
the signal polarity, wheras the pulse width
depend on LAFS, SLEN and xCLKDIV.

a