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Application Report

SPRA755A - July 2002

Getting Started in C and Assembly Code With the

TMS320LF240x DSP

David M. Alter DSP Applications – Semiconductor Group

ABSTRACT

This application report presents basic code for initializing and operating the TMS320LF240x

†

DSP devices. Two functionally equivalent example programs are presented: one written in

assembly language and the other in C language. Detailed discussions of each program are

provided that explain numerous compiler and assembler directives, code requirements, and

hardware-related requirements. The programs are ready to run on either the TMS320LF2407

Evaluation Module (EVM) or the eZdsp LF2407 development kit. However, they are also

intended for use as a code template for any TMS320LF240x

†

(LF240x) or TMS320LF240xA

†

(LF240xA) DSP target system.

Contents

1 Introduction 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2 Hardware Setup 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2.1 LF2407 EVM Setup 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2.2 eZdspE LF2407 Setup 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3 Using the Code Composer GEL File 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4 Overview of the Example Programs 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5 Assembly Language Example Program 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6 C Language Example Program 13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7 Conclusion 20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

8 References 20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Appendix A Assembly Language Example Program Listing 21. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Appendix B C Language Example Program Listing 30. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Appendix C Addendum to Getting Started in C and Assembly Code With the 23

TMS320LF240x DSP 30. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

List of Figures

Figure 1 Assembly Language Example Program Code Flow 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Figure 2 C Language Example Program Code Flow 14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

†

Go to http://www.ti.com for a complete list of TMS320C24x devices.

eZdsp is a trademark of Spectrum Digital Incorporated.

TMS320C24x is a trademark of Texas Instruments.

All trademarks are the property of their respective owners.

SPRA755A

2 Getting Started in C and Assembly Code With the TMS320LF240x DSP

1 Introduction

A hurdle often faced by code developers working with an unfamiliar DSP is knowing how to get

started. A good example program that illustrates proper DSP initialization, interrupt handling,

and peripheral operation can be invaluable. This application report presents basic code for

initializing and operating the TMS320LF240x devices. Although the code herein is designed to

run on either the TMS320LF2407 Evaluation Module (EVM) or the eZdsp LF2407

development kit, it is also applicable, and intended for use, as a code template for any

TMS320LF240x (LF240x) or TMS320LF240xA (LF240xA) DSP target system.

This application report presents two functionally equivalent example programs: one written in

assembly language, and the other written in C programming language. A reader who possesses

an understanding of one of these two languages can compare the two programs to understand

the coding in the other language. The philosophy behind the code examples is to keep them as

simple and clear as possible. Therefore, only a few of the numerous peripherals on the LF2407

DSP are exercised. The assumption is that once the basic coding techniques for configuring a

peripheral register are illustrated, the reader can easily duplicate the code to configure any other

peripheral.

In addition to the example programs, two complete header files are provided that define the

addresses of all user-programmable registers on the LF2407 DSP: one for assembly code and

the other for C code. Finally, a Code Composer v4.1x gel file is provided (along with usage

instructions) that conveniently places all LF2407 peripheral registers into a Code Composer

menu for easy inclusion into a debugger watch window.

2 Hardware Setup

The example programs in this application note are designed to run out-of-the-box on either the

LF2407 EVM or eZdsp LF2407. If you do not have one of these boards, all of the benefits of

the example programs are still available to you. You simply may not be able to run the programs

without making modifications to them for your particular target board.

2.1 LF2407 EVM Setup

The example programs are ready to run on the LF2407 EVM board without any modification. It is

assumed that the reader already has the EVM board, an emulator (e.g., XDS510PP-plus from

Spectrum Digital Inc. or XDS510) and a debugger (e.g., Code Composer v4.10 or v4.12)

installed on a PC and ready to go. It is beyond the scope of this application report to provide

direction on tools installation. Please see the installation instructions that came with the tools for

assistance with this.

Numerous jumpers exist on the EVM board. The following are jumper setting requirements for

proper operation of the example programs:

• JP5: This jumper controls the voltage level of the VCCP pin on the DSP. Normally, leave it in

the 1–2 position. If you want to program the FLASH with the example program, set to the

2–3 position during FLASH programming. It is good practice to return it to the 1–2 position

after FLASH programming.

Code Composer is a trademark of Texas Instruments.

SPRA755A

Getting Started in C and Assembly Code With the TMS320LF240x DSP

• JP6: This jumper controls the voltage level of the MP/MC pin on the DSP. Normally, set to

the 1–2 position to use the external RAM in place of the internal FLASH. Set to the 2–3

position if you want to program the FLASH with the example program, and leave in the 2–3

position to run the program out of the FLASH after it is programmed.

• JP13: Set to the 1–2 position. This uses the clock oscillator on the EVM board.

• JP16: Set to the 1–2 position. This disables bootloading.

All other jumper settings are don’t cares for the example programs, since those jumpers affect

peripherals that are not used here (e.g., CAN, SPI, ADC, or SCI). Additional information on

these jumpers can be found in reference [7].

The LF2407 EVM is assumed to contain a 7.3728 MHz on-board oscillator. The example

programs configure the DSP phase-locked loop (PLL) for multiply-by-four mode, which gives a

CPU clock of 29.49 MHz (i.e., 30 MHz). The values stated in this report for the PWM carrier

frequency, GPIO toggle period, and LED bank update rate have been computed assuming a 30

MHz CPU clock. If a different oscillator value is used, these values will be different. In addition,

one must be careful not to exceed the rated clock speed of the DSP in use (30 MHz for current

LF240x devices or 40 MHz for current LF240xA devices). Some early LF2407 EVM boards used

15 MHz oscillators that exceed the 30 MHz DSP rating if multiplied by four with the PLL. All you

need to do in this situation is edit the example programs so that the PLL is configured for

multiply-by-two mode instead. This setting is selected by bits 11–9 in the SCSR1 register. These

bits are currently written as 000b. Change these to 001b to get the multiply-by-two PLL (see

discussions for program lines 114 and 572 in sections 5 and 6, respectively, of this document).

Also, some of the newest EVMs may have been fitted with a 40 MHz LF2407A DSP and use a

10 MHz oscillator. No program change is necessary here, although again timing values for the

PWM, GPIO toggle, etc., will differ from those stated in this report (i.e., they will be 33% faster).

For more information on the PLL and the SCSR1 register, see reference [2], pages 2–3 to 2–5.

2.2 eZdsp LF2407 Setup

The example programs are ready to run on the eZdsp LF2407 board (henceforth referred to as

eZdsp) without any modification. It is assumed that the reader already has the eZdsp and its

debugger software installed and ready to go. It is beyond the scope of this application report to

provide direction on tools installation. Please see the installation guide that came with the tools

for assistance with this.

Several jumpers exist on the eZdsp board. The following are jumper setting requirements for

proper operation of the example programs:

• JP3: This jumper controls the voltage level of the VCCP pin on the DSP. Normally, leave it in

the 1–2 position. If you want to program the FLASH with the example program, set to the

2–3 position during FLASH programming. It is good practice to return it to the 1–2 position

after FLASH programming.

• JP4: This jumper controls the voltage level of the MP/MC pin on the DSP. Normally, set to

the 1–2 position to use the external RAM in place of the internal FLASH. Set to the 2–3

position if you want to program the FLASH with the example program, and leave in the 2–3

position to run the program out of the FLASH after it is programmed.

All other jumper settings are don’t cares for the example programs, since those jumpers affect

the ADC peripheral and the ADC is not used by the example programs. Additional information

on these jumpers can be found in reference [8].

SPRA755A

4 Getting Started in C and Assembly Code With the TMS320LF240x DSP

The eZdsp is assumed to contain a 14.7 MHz on-board oscillator. The on-board FPGA then

implements a divide-by-two, such that a 7.35 MHz clock signal is ultimately fed into the LF2407

DSP. The example programs configure the DSP phase-locked loop (PLL) for multiply-by-four

mode, which gives a CPU clock of 29.4 MHz (i.e., 30 MHz). The values stated in this report for

the PWM carrier frequency, GPIO toggle period, and LED bank update rate have been

computed assuming a 30 MHz CPU clock. If a different oscillator value is used, these values will

be different. In addition, you must be careful not to exceed the rated clock speed of the DSP in

use (30 MHz for current LF240x devices, or 40 MHz for current LF240xA devices). For example,

if you are using a 30 MHz oscillator instead of the standard 14.7 MHz one, using the

multiply-by-four PLL mode would exceed the 30 MHz frequency rating of the LF2407 DSP. All

you need to do in this situation is edit the example programs so that the PLL is configured for

multiply-by-two mode instead. This setting is selected by bits 11–9 in the SCSR1 register, and

these bits are currently written as 000b. Change these to 001b to get the multiply-by-two PLL

(see discussions for program lines 114 and 572 in sections 5 and 6, respectively, of this

document). For more information on the PLL and the SCSR1 register, see reference [2], pages

2–3 to 2–5.

3 Using the Code Composer GEL File

The file lf2407.gel is provided with this application report download. This is a script file

containing startup instructions for TMS320C2xx Code Composer v4.1x. Specifically, it has been

tested with v4.10 and v4.12 of this debugger. When installed with Code Composer, it causes all

LF2407 DSP peripheral registers to be listed on the GEL menu inside Code Composer. When a

particular register is selected on this menu (e.g., by clicking on it with your PC mouse), that

aid during code debug, and avoids having to fumble through the user’s guide to look up register

addresses. Note that the peripheral set of the LF2407 DSP is a superset of all other current

240x and 240xA devices. Therefore, this gel file is usable with any 240x or 240xA target.

To use the gel file with Code Composer, place the file in the C:\tic2xx\cc\gel directory on your PC

(assuming you used the default installation paths when you installed Code Composer). Then,

right-click on the shortcut (or Windows 95/98 Start menu item) that you use to invoke Code

Composer. Select Properties, and then click on the Short Cut menu. The Target: box on this

menu should show the following (again assuming default installation paths):

C:\tic2xx\cc\bin\cc_app.exe C:\tic2xx\cc\gel\init.gel

To use the lf2407.gel file, simply change the Target: box to read:

C:\tic2xx\cc\bin\cc_app.exe C:\tic2xx\cc\gel\lf2407.gel

4 Overview of the Example Programs

There are two functionally identical programs provided. The first is written in TMS320C2xx DSP

assembly language, while the second is written in C programming language. Each example

program has been tested on both the LF2407 EVM and the eZdsp LF2407. Code generation

was performed using the TMS320C2x/C2xx/C5x Code Generation Tools PC v7.00, with C2xx

Code Composer Software Package PC v4.12 as the debugger. The C example program was

tested with compiler optimization disabled, and also with level 3 (–o3) optimization.

SPRA755A

Getting Started in C and Assembly Code With the TMS320LF240x DSP

Each example program performs the following tasks on the DSP:

• Configures the two System Control and Status registers

• Disables the Watchdog Timer

• Configures the external memory interface

• Configures the shared device pins

• Configures GP Timer 1 and the compare units to provide 20KHz, 25% duty cycle symmetric

PWM on the PWM1 pin. This can be observed by connecting an oscilloscope to the

PWM1/IOPA6 signal located on the EVM and eZdsp signal headers.

• Configures GP Timer 2 to provide a 250ms interrupt

• Configures the core and event manager interrupt registers, and enables global interrupts

• In the GP Timer 2 interrupt service routine, the following is performed:

– Context save/restore using a software stack

– The quad LED bank on the EVM is sequenced (250 ms update rate). This is visible only

on the EVM, since the eZdsp does not have the quad LED bank. However, no

modifications to the program are necessary for operation on the eZdsp. The LED

update instructions produce a benign write to I/O space on the external memory interface

of the DSP when using the eZdsp.

– The IOPC0 pin is toggled, producing a 2 Hz (500ms) square wave. On the EVM, the

IOPC0 pin is connected to the red LED labeled DS1 on the board. On the eZdsp, the

IOPC0 pin is connected to the red LED labeled DS2 on the board. Users can visually see

the pin toggle by observing the LED. Alternately, an oscilloscope can be connected to the

W/R

/IOPC0 pin on the EVM and eZdsp signal headers.

In addition, the example programs illustrate the following concepts:

• How to work with multiple files

• How to work with multiple code sections

• How to write an interrupt service routine using either C or assembly language

• How to insert inline assembly code into a C language program

• How to access the I/O space using either C or assembly language

• How to access peripheral registers using either C or assembly language

• How to use include files

• Complete core interrupt vector tables for C and assembly language programs

• Example LF2407 DSP linker command files for both C and assembly language programs

Finally, note that besides running from external memory, each example program can be

programmed into the internal FLASH memory on the LF2407 DSP and run out of the FLASH on

either the LF2407 EVM or the eZdsp LF2407, without the need for any file modifications.

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