Analog Devices ee-14 Application Notes

Engineer To Engineer Note EE-14

Notes on using Analog Devices’ DSP, audio, & video components from the Computer Products Division

Phone: (800) ANALOG-D or [phone], FAX: [phone], EMAIL: [e-mail]

C Programs on the ADSP-2181 EZ­KIT LITE

Last Modified: 5/6/96

This DSP EZ-Note explains in detail a basic ADSP-2100
family C program. This C routine provides a simple shell
for use with the ADDS-21XX-EZ-LITE. The EZ-LITE is
the low-cost ADSP-2181 based evaluation board. While the
EZ-LITE comes with software, it does not include the C
compiler. So this EZ-Note assumes that you have the
complete version of the Analog Devices software (ADDS­21XX-SW-PC). The current version of the software is
release 5.1.

Our main C program is CTIP35.C. As you can see from
the listing, individual lines have been numbered. The lines
are explained in the corresponding sections below.
CTIP35.C when run on the EZ-LITE takes the input from
the AD1847 stereo codec called LEFT_IN and RIGHT_IN
and loops it back to the 1847 by writing to LEFT_OUT
and RIGHT_OUT. You can add on to this simple talkthru
program by modifying the inputs before writing to the
outputs.

The file CTIP35.ZIP contains all the system files needed to
test this application on your own EZ-LITE system.
CTIP35.ZIP is available on the FTP site. Files included
in the ZIP file are:

CTIP35.C
SIGNAL.H,
2181_HDR.DSP
TALK_47.DSP
BUILD.BAT

2181.ACH

switches. And finally 2181.ACH is an architecture file that
can be used with the EZ-LITE.

For more information on C coding with the Analog
Devices’ DSPs refer to the C tools manual, the ADDS­21XX-SW-PC release note.

1) Extensions to the ANSI C compiler

The Analog Devices GNU based C compiler conforms to
the ANSI C standard. However, there are additions or
extensions to the ANSI C language that are specific to the
ADSP processors. The instruction:

volatile int left_in, right_in;

is an example of an extension to the int data type. Using
volatile will force the DSP to place the variables left_in
and right_in into memory locations -- as opposed to
manipulating the data in registers only. Another extension
to ANSI C is the PM data type. Using the data type:

int pm coeff[10];

will create a buffer in the DSP’s program memory for
storing coefficients. Without the pm extension all data will
be placed in data memory.

2) Accessing memory-mapped registers in C

The DSP reserves a section of internal memory for
configuration registers. Configuring the serial ports,
internal timer, IDMA, BDMA, memory wait states, etc. is
accomplished by writing to these memory mapped
registers. To accomplish this in C, use a #define command
to create a label or pointer for the memory location. In our
CTIP35.C program we’re initializing the wait states for the
IO memory space using:

The file TALK_47.DSP is an assembly routine that is
called by CTIP35.C and initializes the interface between
the ADSP-2181 and the AD1847. The file SIGNAL.H is a
header file that contains macros for handling interrupts.
2181_HDR.DSP contains a modified run-time header for
the 2181. BUILD.BAT is a batch file that assembles
2181HDR.DSP and then invokes the C compiler and all its

CTIP35.C

/* CTIP 35 */
/* this program can be used as a shell for C programs running on the
EZ-LITE board or as an basic example of C code */

#define DM_Wait_Reg *(int *) 0x3ffe.

Then in the code, you can write to that memory location
using:

DM_Wait_Reg=0x0fff;

3 #include <signal.h>
2 #define DM_Wait_Reg *(int *) 0x3ffe

5 extern init_1847();
3 void new_sample();

4 asm(".var/dm/ram/circ rx_buf_[3]; /* Status + L data + R data */\n"\
4 "\t.var/dm/ram/circ tx_buf_[3]; /* Cmd + L data + R data */\n"\
4 "\t.init tx_buf_: 0xc002, 0x0000, 0x0000; /* Initially set MCE */\n"\
4 "\t.global rx_buf_, tx_buf_;");

1 volatile int left_in, right_in;
1 volatile int left_out, right_out;

int stat_flag;

void main()
{

5 init_1847(); /* initialize 1847 interface */

4 asm("set fl1;"); /* set LED on EZ-LITE */

2 DM_Wait_Reg=0x0fff;

3 interrupt(SIGSPORT0RECV, new_sample);

6 while(1){

6 asm("idle;"); /* wait for an interrupt */

6 right_out=right_in; /* loop back for talk-thru */
6 left_out=left_in;

}
}

3 void new_sample()

{
4 asm("ena sec_reg;");
4 asm("ax0 = dm(rx_buf_+1);"); /* receive new sample */
4 asm("ax1 = dm(rx_buf_+2);");
4 asm("dm(left_in_) = ax0;"); /* write to memory */
4 asm("dm(right_in_) = ax1;");

4 asm("ax0 = dm(left_out_);"); /* read output sample */
4 asm("ax1 = dm(right_out_);");
4 asm("dm(tx_buf_+1) = ax0;"); /* transmit to codec */
4 asm("dm(tx_buf_+2) = ax1;");

4 asm("dis sec_reg;");

}

EE-14 Page 2

Notes on using Analog Devices’ DSP, audio, & video components from the Computer Products Division

Phone: (800) ANALOG-D or [phone], FAX: [phone], EMAIL: [e-mail]