EE 451 Lab 3: Interrupts and Visualization Tools - Prof. Hector Erives | Lab Reports Digital Signal Processing

EE451L Fall 2008

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EE 451 – LAB 3

Interrupts and Visualization Tools

In this laboratory you will use hardware and software interrupts in the C6713. You will also use

visualization tools available in the CCS.

Introduction

In previous labs you have been using the polling method to generate a signal with the C6713. In

polling mode, a function polls, or tests, the Transmit Ready bit (XRDY) of the MCBSP serial port

control register (SPCR), until this indicates that the codec is ready to receive a new output

sample. A new output sample is sent to the codec using the function MCBSP_write( ). Although

polling is simpler than the interrupt technique, it is less efficient since the processor spends

nearly all of its time repeatedly testing whether the codec is ready to transmit data. In the

interrupt mode, an interrupt stops the current CPU process to that it can perform a required task

initiated by an interrupt, and it is redirected to an interrupt service routine (ISR).

The DSP/BIOS real-time operating system available on the CCS provides real-time scheduling,

analysis, and data transfer capabilities for an application running on the DSP. The DSP/BIOS

has a preemptive real-time scheduler that determines which one of a number of different threads

is executed by the DSP at any given time. Threads are DSP/BIOS objects that contain program

code (functions). There are five different threads that can be used in a DSP/BIOS application:

•Hardware interrupts (HWIs) have the highest priority. Their execution is triggered by

interrupts from peripherals and they always run to completion.

•Software interrupts (SWIs) are triggered from within a program. They run to completion

unless preempted by a high priority SWI or HWI.

•Periodic functions (PRDs) are a special type of SWI triggered by a dedicated hardware

timer.

•Tasks (TSKs) are created dynamically within a DSP/BIOS application, and they will start

execution at the start of the DSP/BIOS application.

•Idle functions (IDLs) are executed repeatedly as a part of the lowest priority thread. They

contain functions that communicate real-time data analysis from the DSP to the host.

The C I/O functions make it possible to access the host’s operating system to perform I/O. The

capability to perform I/O on the host gives you more options when debugging and testing code.

However, calls to the C function printf() are computationally too expensive to be used within a

real-time program. A LOG object inserted into a DSP/BIOS application sets up a buffer to

which the function LOG_printf() can be used to append messages. The buffer contents are sent

to a host computer in real time as part of the idle loop.

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EE 451 – LAB 3

Interrupts and Visualization Tools In this laboratory you will use hardware and software interrupts in the C6713. You will also use visualization tools available in the CCS. Introduction In previous labs you have been using the polling method to generate a signal with the C6713. In polling mode, a function polls, or tests, the Transmit Ready bit ( XRDY ) of the MCBSP serial port control register (SPCR), until this indicates that the codec is ready to receive a new output sample. A new output sample is sent to the codec using the function MCBSP_write ( ). Although polling is simpler than the interrupt technique, it is less efficient since the processor spends nearly all of its time repeatedly testing whether the codec is ready to transmit data. In the interrupt mode, an interrupt stops the current CPU process to that it can perform a required task initiated by an interrupt, and it is redirected to an interrupt service routine ( ISR ). The DSP/BIOS real-time operating system available on the CCS provides real-time scheduling, analysis, and data transfer capabilities for an application running on the DSP. The DSP/BIOS has a preemptive real-time scheduler that determines which one of a number of different threads is executed by the DSP at any given time. Threads are DSP/BIOS objects that contain program code (functions). There are five different threads that can be used in a DSP/BIOS application:

Hardware interrupts ( HWIs ) have the highest priority. Their execution is triggered by interrupts from peripherals and they always run to completion.
Software interrupts ( SWIs ) are triggered from within a program. They run to completion unless preempted by a high priority SWI or HWI.
Periodic functions ( PRDs ) are a special type of SWI triggered by a dedicated hardware timer.
Tasks ( TSKs ) are created dynamically within a DSP/BIOS application, and they will start execution at the start of the DSP/BIOS application.
Idle functions ( IDLs ) are executed repeatedly as a part of the lowest priority thread. They contain functions that communicate real-time data analysis from the DSP to the host. The C I/O functions make it possible to access the host’s operating system to perform I/O. The capability to perform I/O on the host gives you more options when debugging and testing code. However, calls to the C function printf() are computationally too expensive to be used within a real-time program. A LOG object inserted into a DSP/BIOS application sets up a buffer to which the function LOG_printf() can be used to append messages. The buffer contents are sent to a host computer in real time as part of the idle loop.

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The Lab Create a program that uses an ISR to read a signal from LINE IN and output it through the LINE OUT in real-time. Connect the function generator to the LINE IN input and verify that the program can reproduce the signal at the LINE OUT. Part 1: Hardware Interrupts (HWIs) 1 Start CCS and begin a new project. You may use the same program template you used in the previous laboratory with some changes. You need to delete the statement while(1). There is no need to supply an explicit idle loop in a DSP/BIOS application. Modify the main() function to include the set up required to use interrupts, as depicted in Figure 1. 2 Create and add a configuration file to the project. Select File → New → DSP/BIOS Configuration. Select dsk6713.cdb as the template. Expand Scheduling and HWI – Hardware Interrupt Service Routine Manager and click on HWI_INT11. Right-click on HWI_INT11 and select properties to set the function to the ISR (in the sample template shown in Figure 1, it will be “_generate_sample”). Under the dispatcher tab, check Use Dispatcher. Note: there has to be an underscore preceding the name of your ISR. 3 Select Project → Build Options to the Compiler and Linker options. In the Advanced category of compiler options set the Memory Model option to Far Calls & Data. 4 Set the function generator to output a sinusoidal signal and connect it to the LINE IN of the board. 5 Connect an oscilloscope to the LINE OUT of the board and make sure the board is patching through the signal. Part 2: Visualization Tools 1 Modify your code and use the printf() function to display the data from the function generator. 2 Turn on the CPU Load Graph from the DSP/BIOS → CPU Load Graph, run your code and record the CPU load. What is the CPU load? 3 Now we will create a log event. Add the following code to your program: #include <log.h> extern LOG_Obj LOG_YourLogVariable; 4 You need to print the value from the LINE IN input using a LOG_printf() function.

EE 451 Lab 3: Interrupts and Visualization Tools - Prof. Hector Erives, Lab Reports of Digital Signal Processing

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EE 451 – LAB 3

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