Lab 3 - Debugging on Hardware

 Objective

This lab steps through several procedures to teach the following:

  • How to select the appropriate debugger/programmer
  • How to download firmware (including the debug executive) into a PIC® MCU
  • How debugging techniques on hardware compare to simulator debugging
  • How to directly control SFRs and alter program variables on a PIC® MCU during operation
  • How to remove the debug executive from a project and create a customer deliverable HEX which runs without a debugger/programmer

 Materials

Hardware Tools (Optional)

Tool About Purchase
Explorer16-50px.png
Explorer 16
Development Board
ICD3-50px.png
MPLAB® ICD 3
In-Circuit Debugger

Software Tools

Tool About Installers
Installation
Instructions
Windows Linux Mac OSX
MPLAB® X
Integrated Development Environment
MPLAB® XC16
C Compiler
Proteus VSM
Visual, Interactive Simulator Demo

Exercise Files

The contents of the following zip file need to be placed in this directory:
C:\MTT\TLS0101

File Download
Installation
Instructions
Windows Linux Mac OSX
Project and Source Files

 Procedure

1

Open Lab03

Close any open projects by right clicking on the project name and selecting “Close”

Click the Open Project Main_Open_Project.png icon

Browse to C:\MTT\TLS0101\Lab03.X and select Open Project

Double click on Lab03.c under Source Files to open the C file in the editor window

Lab03.png

Notice the variable delayVal. This variable is defined with an initial value of decimal 10. This variable, delayVal, is used to control the execution time of the delay() function. We will alter this variable in the latter part of Lab03.

2

Verify the Hardware Tool

If you wish to run this lab on hardware this is where you need to select your debugger/programmer.

Verify the Hardware Tool assigned to this project is the Proteus VSM Viewer (if you don't have hardware) or REAL ICE/ICD3 (if you have hardware).

NewProteus2.png

Right click on Lab03 from the project list

Select Properties

Under the Conf:[default] section ensure the Proteus VSM Viewer or REAL ICE / ICD3 has been selected.

Click OK ok.png

3

Verify the debug session will start at the beginning of main()

HaltAtMain.png

Tools -> Options -> Embedded -> “Generic Settings” -> Debug startup -> Halt at Main

4

Debug Project

Click Debug Project Main_Debug_Project.png icon to build a debug image and download it to the VSM Viewer / REAL ICE / ICD3. You will notice the project builds, and then starts the VSM View or programs the Explorer16 processor through the REAL ICE / ICD3
ProteusWindow.png
Lab3Code.png

Above we see the editor window showing Lab03.c after simulation ready to continue at the beginning of main().

5

Set Breakpoints

Set breakpoints on the two LATA assignment statements within the while(1) loop

Click on the left margin of lines of code containing LATA=0xAA; and LATA = 0x55;

TwoBreakpoints.png
Click the Continue Debug_Continue.png icon to run the program until the first breakpoint is encountered

You should notice the green bar on the line with the breakpoint set

GreenBarOnBreakpoint.png

Skid on breakpoint. When running on hardware, the PIC MCU may execute the instruction at the breakpoint and THEN stop. Under software simulation, the CPU halts BEFORE the instruction is executed. Stopping after executing the breakpoint instruction is referred to as a Skid.

If the green bar is located below the red bar you are observing a “skid”. The red bar indicates where the break point was set and the green bar is where the processor stopped. Depending on the particular version of MPLAB® X IDE and the debugger, you will need to take this skid onto consideration when debugging on hardware.

6

Operation of Program

Click the Continue Debug_Continue.png icon to move the program to the next breakpoint. Each time the PIC MCU stops at a break point, observe the LEDs on the VSM implementation of the Explorer16 change. Repeat this step several times until you are familiar with the operation of this program.

7

Remove Breakpoints from the Code

From the Window menu select Debugging, then Breakpoints

BreakpointsPath.png

Right click in the Breakpoint Window and select Delete All

Breakpoints.png
Click the Continue Debug_Continue.png icon to run the project code on hardware at full speed

Do you see the LEDs blink or do they appear to stay on constantly? At question is the speed of the processor. The clock rate of the PIC MCU is such that the delay() function executes so quickly the human eye cannot easily notice the toggling of the LEDs. To adjust the speed we will manually adjust the variable delayVal using MPLAB X IDE.

Pause the Simulation by clicking the Pause Debug_Pause.png icon

8

Adding Variables to the Watches Window

Open the Watch Window (if not already open) by selecting it from the Window menu. Watches from previous labs might show up (right-click and select Delete All)

WatchesPath.png

Within the Watch Window right click and select New Watch…

NewWatch.png

Highlight the “Global Symbols” radial button

Select the variable delayVal from the menu

Click “OK” ok.png
GlobalSymbols.png

If LATA is not already in the Watch window repeat the above step to add this SFR to the list of data points to watch

WatchWindow.png

You may notice delayVal is displayed with a value of “0x00AA” and not “10” as written in the source code. The Watch window will default to display values in HEX while the value in the code was decimal. To synchronize the value in the Watch window with what radix we coded we will change the display on the Watch Window

9

Changing the Radix of the Watches Window

Within the watch Window Right Click on ‘delayVal’

Move the mouse over Display Value As and select Decimal

Decimal.png

Highlight the Value displayed for delayVal (in this case 10)

Change the number to 2048 then press Enter

2048.png
Click Continue Debug_Continue.png and notice slower LED blinking. Pause the simulation by clicking Pause Debug_Pause.png

10

Saving Changes

To save the changes we need to enter the new delayVal into the source code

Change the line of coding reading delayVal = 10; to delayVal = 2048;

SavingValues.png

Before we rebuild and then run the code we will manually control the SFRs on the PIC MCU. Directly controlling the contents of SFRs can be very useful during the debugging process. For today’s lab we will manually alter the LATA SFR to allow a different pattern to be displayed on the LEDS.

In the Watch Window enter 0x003C

LataValue.png

Notice an immediate change in SFR value as displayed on the LEDS

LedPattern.png
End the debug session Debug_Finish_Debugger_Session.png

11

Make and Program Device

Build and run a production version of the code by Clicking the Make and Program Device Main_Program_Target_Project.png icon. This will remove the debug executive and build a version of the code which will run without the prompting from a debugger. Please note this step will only work if you are using a programmer debugger such as the PICkitTM3, MPLAB® ICD3, or MPLAB® REAL ICE.

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