Analog Devices ee-140 Application Notes

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Using the ADSP-21160 Serial
Ports in Multi-channel Mode.

Last Modified: August 2001

Introduction

The purpose of this document is to aid in and
provide an example of using the ADSP-21160
serial ports in multichannel mode. The
examples given were tested on two ADDS­21160M-EZLITEs. The code was developed
using VisualDSP++1.0. Two code examples
are provided. The first is a simple example of
how to use multichannel mode. The second
example adds the Receive Register Comparison
functionality.

Hardware Setup

The hardware connection of the two serial ports
is described below:

DSP1 DSP2

DTx Í=======Î RTx

DRx Í=======Î DTx

RFSx Í=======Î RFSx

TFSx unconnected TFSx

TCLKx Í=======Î TCLKx

RCLKx Í=======Î RCLKx

Additionally, the TCLKx and the RCLKx of
DSP1 should be tied together, and the TCLKx
and RCLKx of DSP2 should be tied together.
Essentially, all four clocks will be connected.

Engineer To Engineer Note EE-140

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

In this test case, DSP1 will be internally
generating RCLK and RFS. All other frame
syncs and clocks in this system are set to be
externally generated. It is important to note that
in multichannel mode, the frame sync and clock
should always be generated by the RFS and the
RCLK and not the TFS or the TCLK. The TFS
pin is often left unconnected, although it can be
used as a data valid pin. TCLK should always
be configured as an input in multichannel mode.
In this example, both hardware platforms are
using serial port 0.

Software Description

Listed at the end of this document is code for
DSP1 and DSP2. In this example, both DSPs
have sixteen 32 bit channels set up in their serial
port control registers. It is important to note that
in multichannel mode, both the SRCTLx
register and the STCTLx register must have the
same serial word length programmed.

When using multichannel mode, any channel
can be used to transmit or receive. In this
example, DSP1 is transmitting on the first eight
channels, and DSP2 is receiving on the first
eight channels (set up in the MTCS0 and the
MRCS0 registers). The DMA on DSP1 is set up
to transmit 16 words. Since there are only 8
channels activated, there will be two frame
syncs being generated. (The first frame sync is
generated, then the first eight words are sent
over the eight channels. Then the next frame
sync is generated and the second eight words are
sent over the same eight channels.) DSP2 is set
up in the same way, except to receive.

Copyright 2001, Analog Devices, Inc. All rights reserved. Analog Devices assumes no responsibility for customer product design or the use or application of customers’ products or
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When running these two programs, DSP2
should be started first. This allows time for the
serial port to be configured before the frame
sync and data starts coming from DSP1.

In this system, the clock is being generated by
DSP1’s SRCTL0 register. Therefore bit 10 of
the SRCTL0 register is set. Since DSP1 is only
transmitting data, and not receiving, bit 18
(SDEN) is set in the STCTL0 register to enable
a DMA, but not the SRCTL0 register.

Note that in multichannel mode several bits of
the SRCTLx registers and the STCTLx registers
must be cleared. These are bit 0 (SPEN), bit 10
(ICLK), bit 13 (TFSR), bit 14 (ITFS), and bit 17
(LAFS) in the STCTLx. In the SRCTLx
register, bit 0 (SPEN), bit 13 (RFSR), bit 17
(LAFS), bit 21 (D2DMA) and bit 22 (SPL) all
must be cleared.

SPORT Receive Comparison
Registers

When in multichannel mode, the serial ports can
take advantage of the receive comparison
registers. This enables the DSP to compare the
data coming in to the serial port and compare it
to a know value. Depending on the outcome of
this comparison, the DSP will either save the
word, or discard it. This functionality can be
used for interprocessor communication when
connecting together several DSPs via the serial
port. (See the ADSP-21160 Hardware
Reference, page 9-33 for a an example of how
this can be done)

To enable the comparison registers, bit 15
(IMODE) in the SRCTLx register must be set.
Bit 20 (IMAT) controls what happens to the
incoming data word after comparison. If this bit
is cleared, the data is accepted if the comparison
is false. If the bit is set, the data is accepted if
the comparison is true. Note that in single
channel mode, both bit 15 and bit 20 have
different functions. They assume their Receive
Comparison Register control functionality when
the serial port is programmed in multichannel
mode.

The word to be compared to is placed in the
KEYWDx register. Specific bits can be masked
out of the comparison by setting the
corresponding bit in the KEYMASKx register.
The MTCCSx register, which is used for
companding channel selection when not in
comparison mode, is used to select the channels
that will be compared with KEYWDx. If a bit
in the MTCCSx register is cleared, then the
corresponding channel does not go through the
comparison process and instead is always
accepted. If the bit is set, then the DSP
performs the comparison on the corresponding
channel.

Example code for DSP2 which uses the receive
comparison registers is included at the end of
this document. In this example, the data value
that is placed in the KEYWD0 register is
0x33333333. Every bit in the MTCCS0 register
is cleared, so every bit in every incoming word
is compared to what is in KEYWD0. The DSP
will then discard any word that comes in to the
serial port that is not 0x33333333. If
0x33333333 is received by the serial port, it is
saved to memory. Additionally, an interrupt can
be set up to be triggered any time there is a
KEYWDx match.

Example Code for DSP1

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/*Code for DSP1*/
/*In this example, DSP1 functions entirely as a transmitter*/
#include <def21160.h>
#define N 16 /* Size of buffer */

.section/DM seg_dmda;
.VAR source[N]=
0x11111111, 0x22222222, 0x33333333, 0x44444444,
0x55555555, 0x66666666, 0x77777777, 0x88888888,
0x99999999, 0xAAAAAAAA, 0xBBBBBBBB, 0xCCCCCCCC,
0xDDDDDDDD, 0xEEEEEEEE, 0xFFFFFFFF, 0x00000000;

/* PM interrupt vector code */
.section/pm seg_rth;
Reserved_1: rti; nop; nop; nop;
Chip_Reset: idle; jump start; nop; nop;

.section/pm seg_pmco;
start:
/*clear receive and transmit serial port registers*/
r0=0x0;
dm(STCTL0)=r0;
dm(SRCTL0)=r0;

r0 = 0x000000FF; /*Enable 1st 8 channels for transmit */
dm(MTCS0) = r0;

r0 = 0;
dm(MTCCS0) = r0; /* no companding on transmit */
dm(MRCCS0) = r0; /* no companding on receive */
dm(MRCS0) = r0; /* receive on no channels */

r0=0x0;
dm(TDIV0)=r0;
r0 = 0x03e70001; /* 20MHz SCLK, 20KHz RFS */
dm(RDIV0)=r0;

/*configure the DMA*/
r0=source;
dm(II2) = r0; /*internal memory location */
r0=1;
dm(IM2) = r0; /* stride is 1 */
r0=16;
dm(C2) = r0; /*move 16 words*/

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