1. Writing Portable and Robust Firmware in C
Embedded System Design Techniques™
Writing Portable and Robust Firmware in C
Class 4: Assertions and printf
September 3, 2015 Jacob Beningo, CSDP

2. Course Overview Portable C Concepts Doxygen and PC-Lint
Uart Driver and Stm32CubeMx
Assertions and printf
Robust Firmware Concepts

3. Session Overview printf Overview Problems with printf "Fixing" printf
Assertions
Examples

4. Overview of printf
printf provides a method for formatting and outputing serial data. #include <stdio.h> printf("Hello World!"); printf("The value of x is %d", x); printf("The value of x is %d, y is %d", x, y); printf("The value of pi is %3.2f", 3.14);

5. printf Capabilities %[flags][width][.precision][length][specifier]
Output
Example c
Character k
d or i
Signed decimal integer
392 e
Scientific notation (mantis/exponent) using e character
3,93E+002 E
Scientific notation (mantis/exponent) using E character f
Decimal floating point
392,65 g
Use the shorter of %e or %f 392,65 G
Use the shorter of %E or %f 392,65 o
Signed octal 610
610 s
String of characters sample
sample u
Unsigned decimal integer 7235
7235 x
Unsigned hexadecimal integer 7fa
7fa X
Unsigned hexadecimal integer (capital letters) 7FA
7FA p
Pointer address B800:0000
B800:0000 n
Nothing printed. The argument must be a pointer to a signed int, where the number of characters written so far is stored. %
A % followed by another % character will produce a % character

6. Examples
Requires:
stdarg.h
stdio.h
string.h

7. Issues with printf Have to pull in standard library
ROM and RAM usage will increase
Simple printf statements can affect the real-time performance of the system
Limited number of printf's that can be added to a system
Requires changing code to get useful data out during a debug session

8. Timing Measurements of printf
printf("Hello World!");
12.5 ms
printf("The System state is %d", State);
21 ms

9. "Fixing" printf

10. "Fixing" printf – nonblocking setup
Minimum Time
Maximum Time

11. "Fixing" printf – nonblocking ISR
Interrupt Frequency
~ 1 ms
ISR Execution Time
35 us

12. What is the difference between a bug and an error condition?
Assertions
An assertion is a Boolean expression at a specific point in a program that will be true unless there is a bug in the program.
Pros of ASSERT()
Cons of ASSERT()
improve testing
bugs are easier to detect
execution stops at them
can serve as executable comments
improve code quality
can be turned on and off
slow down code execution
commonly misunderstood
used improperly for error handling
use string that require RAM/ROM
require printf and a terminal
can be turned on and off
What is the difference between a bug and an error condition?

13. Assertion Use If the expression is true, execution continues normally
If the expression is false, whatever happens is "undefined"
Proper Use:
void CalculateDistance(uint8_t Velocity) {
ASSERT(Velocity < 150); }
Improper Use:
int result = Open("MyFile.txt", 'r');
ASSERT(result != NULL);
Mistakes:
ASSERT(result = 14);
ASSERT(VelocitySet(50) < VELOCITY_MAX);

14. Assert.h
__DO_NOT_LINK_PROMISE_WITH_ASSERT, __ASSERT_MSG

15. Assertion Setup

16. Assertion Setup Uart_printf is interrupt driven implementation
May want to map standard printf

17. Testing the assertion

18. Testing the assertion

19. Additional Resources Download Course Material for
Updated C Doxygen Templates (May 2015)
Example source code
Templates
Microcontroller API Standard
EDN Embedded Basics Articles
Embedded Bytes Newsletter
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