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Low-Cost Debugging
for the poor who are not rich nor
wealthy and who do not have a lot of
money to spend, even on food
October 24, 2013
www.elektor-labs.com/low-cost-debugging
Presented by
Clemens Valens
• CEO Elektor.Labs
• Contributing editor
mmmh!
October 24, 2013
www.elektor-labs.com/low-cost-debugging
About Elektor
Electronics magazine for people passionate
about electronics
• 5 main editions:
– English, Spanish, German, French & Dutch
• We publish projects
• We have our own lab
• We design our own PCBs
October 24, 2013
www.elektor-labs.com/low-cost-debugging
Elektor.Labs
• Sharing electronics
• Be an expert, get
rewarded
• Get more out of your
passion
October 24, 2013
www.elektor-labs.com/low-cost-debugging
MCU Debugging on a shoestring
• Lots of cheap microcontroller boards are
available
• Hobbyists are no longer frowned upon by MCU
manufacturers
• Anyone can create embedded applications
October 24, 2013
www.elektor-labs.com/low-cost-debugging
Programming means Debugging
• Time-consuming
• Good tools are expensive
• Effective debugging requires skills
October 24, 2013
www.elektor-labs.com/low-cost-debugging
Use Your Brain →
October 24, 2013
www.elektor-labs.com/low-cost-debugging
Utopia
• Programmers spend 90% of their time
thinking, the remaining 10% is used for typing
code
• Debuggers spend 90% of their time thinking
and only 10% is used for single-stepping
through code
Code for testing!
October 24, 2013
www.elektor-labs.com/low-cost-debugging
Train Your Debug Muscle
October 24, 2013
www.elektor-labs.com/low-cost-debugging
Enter the LED
October 24, 2013
www.elektor-labs.com/low-cost-debugging
Using the LED
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•
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•
•
Make sure it works
Know which leg is the anode
Keep its brightness low
Use dedicated MCU pins
Write a test program to prove that you master
the LED
October 24, 2013
www.elektor-labs.com/low-cost-debugging
Use Macros (or Functions)
Example:
#define DEBUG_LED0_ON PORTB |= 0x01
#define DEBUG_LED0_OFF PORTB &= 0xfe
(or something nicer but with a similar effect)
Done debugging:
#define DEBUG_LED0_ON /* PORTB |= 0x01 */
#define DEBUG_LED0_OFF /* PORTB &= 0xfe */
(or something nicer but with a similar effect)
October 24, 2013
www.elektor-labs.com/low-cost-debugging
Using LEDs
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•
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Set LEDs to a known state at start-up
Use well-defined animations
Activate/deactivate at strategic positions
One debug function per LED per session
Only one well-defined execution path
October 24, 2013
www.elektor-labs.com/low-cost-debugging
Blink from main()
void main(void)
{
// Increment delta_time by timer;
delta_time = 0ms;
DEBUG_LED_OFF;
while (1)
{
if (delta_time==250ms) DEBUG_LED_ON;
else if (delta_time==500ms)
{
DEBUG_LED_OFF;
delta_time = 0ms;
}
}
}
October 24, 2013
www.elektor-labs.com/low-cost-debugging
Don’t Blink from ISRs
Interrupts may continue to tick even if the main
program crashed.
Exception: when testing ISR functionality.
October 24, 2013
www.elektor-labs.com/low-cost-debugging
LEDs are Really Fast
• They can reveal activity on (serial) ports
• Brightness is a measure for duty-cycle
October 24, 2013
www.elektor-labs.com/low-cost-debugging
Build a Logic Level Probe
October 24, 2013
www.elektor-labs.com/low-cost-debugging
No LEDs?
•
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•
•
•
Use a logic level probe
Use a multimeter
Use an oscilloscope
Use your ears
Use your smartphone
October 24, 2013
www.elektor-labs.com/low-cost-debugging
Serial Sound
October 24, 2013
www.elektor-labs.com/low-cost-debugging
Demo!
October 24, 2013
www.elektor-labs.com/low-cost-debugging
The Serial Port
Use a solid connection, f.i. like this:
October 24, 2013
www.elektor-labs.com/low-cost-debugging
The Serial Port
• Create a working putch
• Create a debug putch:
– #define DEBUG_PUTCH
putch
• Only send printable ASCII characters
• Exception: Bell (0x07)
October 24, 2013
www.elektor-labs.com/low-cost-debugging
The Serial Port
• Create a working puts
• Create a debug puts:
– #define DEBUG_PUTS
puts
• Use meaningful strings
• Print program name & version
October 24, 2013
www.elektor-labs.com/low-cost-debugging
The Serial Port
• Keep debug strings short
• Format cleverly
– Use brackets: <>, (), [], {}
– Prefer separators to whitespace
– Use CR/LF
• Lower-case is easier to read
– ‘B8’ looks like ’88’, write ‘b8’ instead
October 24, 2013
www.elektor-labs.com/low-cost-debugging
Following the Call Stack
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•
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Be verbose
Print real function names
Print at function entry and exit
Cover all exit points
October 24, 2013
www.elektor-labs.com/low-cost-debugging
Following Execution Paths
•
•
•
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Be concise
Use single characters like numbers or letters
Increase character along path
Cover all paths
October 24, 2013
www.elektor-labs.com/low-cost-debugging
Example
int16_t foo(int8_t value)
{
DEBUG_PUTCH('0');
if (value<0)
{
DEBUG_PUTCH('1');
if (value<-5)
{
DEBUG_PUTCH('2');
}
else if (value<-3)
{
DEBUG_PUTCH('3');
}
DEBUG_PUTCH('4');
}
DEBUG_PUTCH('5');
return -10*value;
}
October 24, 2013
www.elektor-labs.com/low-cost-debugging
printf
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Comfortable
Needs a lot of memory
Slow
Partly implemented
Platform dependent
Undefined behavior
October 24, 2013
www.elektor-labs.com/low-cost-debugging
printf Coprocessor
October 24, 2013
www.elektor-labs.com/low-cost-debugging
MCU:
void my_printf(int int_count, char *format, ...)
{
va_list ap;
va_start(ap,format);
puts("printf");
// Send keyword word.
puts(format);
// Send format string.
putch('\0');
// Terminate format string.
putch(sizeof(int)); // Send size of int.
putch(int_count);
// Send number of integers.
while (int_count>0) // Send the arguments.
{
send_int(va_arg(ap,int));
int_count -= 1;
}
va_end(ap);
}
my_printf(3,"u=%05u, p=%p, c=%c\r\n",234,0x4321,'$');
October 24, 2013
www.elektor-labs.com/low-cost-debugging
Coprocessor:
void main(void)
{
while (serial_data_available==true)
{
uint8_t ch = read_serial_input();
if (keyword_found(ch)==false)
{
write_serial_output(ch);
}
else
{
if (printf_statement_complete==true)
{
printf(received_format_string,received_arguments);
}
}
}
}
October 24, 2013
www.elektor-labs.com/low-cost-debugging
Complications
• How to handle fast data streams?
• How to handle errors?
As always: use with care
October 24, 2013
www.elektor-labs.com/low-cost-debugging
One Step Beyond
• Build a €$£10,- debug coprocessor:
–
–
–
–
–
Use a proven platform
Use known good libraries
Debug communications (SPI, I²C, other)
Provide stimuli
Measure voltages
October 24, 2013
www.elektor-labs.com/low-cost-debugging
Debug Coprocessor
October 24, 2013
www.elektor-labs.com/low-cost-debugging
The Next Level
• JTAG pod
• In-circuit debugger (ICD)
• In-circuit emulator (ICE)
October 24, 2013
www.elektor-labs.com/low-cost-debugging
Any questions?
October 24, 2013
www.elektor-labs.com/low-cost-debugging
Next Elektor Webinar
Automation and Test using Flowcode presented
by Ben Rowland and Jonathan Woodrow
Thursday November 21, 2013 (15:00 GMT / 16:00 CET)
Check www.elektor.com/webinar for details
or subscribe to our newsletter
www.elektor.com
October 24, 2013
www.elektor-labs.com/low-cost-debugging
Thank you for attending!
Code available at
www.elektor-labs.com/low-cost-debugging
October 24, 2013
www.elektor-labs.com/low-cost-debugging