Object orientering, test driven development og c

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ObjectOrientering,TestDriven
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InfinIT, 21. November 2018
2018-11-21Object Orientering, Test Driven Development og C - InfinIT - Ib Havn, iha@via.dk 1
Ib Havn
B.Sc.E.E.
M.Sc.ITSoftware Construction

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Whatistheproblems withhardwarenear
programming?
– The nearer the hardware the testing difficulties grows
– There are not much help from different tools
– Errors/bugs are difficult to find
– The software are target dependent
– Design for Test is the solution
– Debug Later Programming (DLP) vs Test Driven Development

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Whydoweforgeteverythingwehave
learnedwhenprogramminglow-levelC?
Typical excuses:
1. Hardware near programming is for Electronics Engineers
2. The hardware is not available yet
3. It is not possible to test due to limited target resources
– Test Driven Development (TDD) is not possible on the small target
4. Debugging facilities in the target toolchain is limited
– Debugging is difficult and is done with oscilloscopes, leds, simple printouts
etc.
5. UML is not useful for C-programming

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ObjectOrientedDesignandProgramming
inC
According to Robert C. Martin an OOP language has the following:
1. Encapsulation
2. Inheritance
3. Polymorphism
The first two are easy to obtain in C, the third is a little harder
1. Abstract Data Types (ADT)
2. Nested struct’s
3. Pointer tables
For a complete description how to do use three read
Axel Schreiner’s book: Object-oriented Programming in ANSI-C

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Exampleofcomplete Encapsulation inC

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Exampleofcomplete Encapsulation inC
// Abstract Data Type (ADT)
typedef struct serial_struct *serial_p;
serial_p serial_new_instance(e_com_port_t com_port, uint32_t baud, e_data_bit_t data_bit,
e_stop_bit_t stop_bit, e_parity_t parity, uint8_t rx_fifo_size,
uint8_t tx_fifo_size,
void(*handler_call_back )(serial_p, uint8_t));
e_serial_return_code_t serial_send_bytes(serial_p handle, uint8_t *buf, uint8_t len);
e_serial_return_code_t serial_send_byte(serial_p handle, uint8_t byte);
e_serial_return_code_t serial_get_byte(serial_p handle, uint8_t *byte);
void serial_flush_rx_fifo(serial_p handle);
void serial_flush_tx_fifo(serial_p handle);
This is all the clients using the driver can see:

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ObjectOrientedDesignandProgramming
inC
Why not use UML – A World wide Industry Standard

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SOLIDDesignPrinciples
Robert C. Martin has assembled these five more or less well-known principles together
Single Responsibility Principle (SRP)
– A class should have one, and only one, reason to change
Open Close Principle (OCP)
– You should be able to extend a class’s behaviour, without modifying it
Liskov Substitution Principle (LSP)
– Derived classes must be substitutables for their base classes
Interface Segregation Principle (ISP)
– Make fine grained interfaces that are client specific
Dependency Inversion Principle (DIP)
– Depend on abstractions, not on concretions

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TestDrivenDevelopment(TDD)
TDDState-machine
source: Test Driven Development for Embedded C, James W. Grenning.
Is it possible on small targets?

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SimplifiedDevelopmentProcess
Production
code
(.h,.c)
Cross
Compiler
Target Platform
Hardware
(registers etc.)
Hardware
API(.h)
Cross
Linker
11101
00011
00110
00111
Hardware
libsandothertargetlibs(.so)

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TestDrivenDevelopmentinC
Host
Compiler
Host Platform
Production
code
(.h,.c)
Hardware
API(.h)
Host
Linker
11101
00011
00110
00111
Host
Libs(.so)
ForcedIncludefiles
(.h)
Mock’sandTestCases
(.h,.c,.cpp)
Hardware
(registers etc.)

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Forced include files:
– The pre-processor includes specified files before anything else is included
– We can add macros and definitions that
– Disable target hardware specific things
– Enable hardware fakes
Compiler/pre-processor options
– gcc option (gnu): –include <file to be included>
– cl option (Microsoft): /FI<file to be included>

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All what’s needed to cheat the toolchain for the ATMEGA2560 MCU:
#include <stdint.h>
#define __AVR_LIBC_DEPRECATED_ENABLE__
#define __AVR_ATmega2560__
#define _AVR_SFR_DEFS_H_ 1
// 0x136 is highest address of registers in ATMEGA2560
#define _HIGHEST_REGISTER_ADD0x136
// These global variables (fake hardware registers) needs to be accessible from both C and C++
// Therefore they must be declared in C scope if it is the C++ compiler that access
#ifdef __cplusplus
extern "C" {
#endif
extern uint8_t __avr_reg[_HIGHEST_REGISTER_ADD];
#ifdef __cplusplus
}
#endif

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All what’s needed to cheat the toolchain for an ATMEGA2560 MCU:
// Macros to access the fake hardware registers
#define _SFR_MEM8(mem_addr) (*(uint8_t *)(&__avr_reg[mem_addr]))
#define _SFR_IO8(io_addr) (*(uint8_t *)(&__avr_reg[io_addr]))
// Byte value from bit_no
#define _BV(bit) (1 << (bit))
// Interrupt
#define _AVR_INTERRUPT_H_
#define ISR(vector, ...) void ISR_##vector(void)
#define sei() SREG |= _BV(SREG_I)
#define cli() SREG &= ~_BV(SREG_I)

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Test cases can now check contents of hardware registers
using a test macro: CHECK_EQUAL_C_BITS(expected, actual, mask)
TEST(TEST_HAL, ADPS2AndADPS1isSetAndADPS0isClearedInADCSRAAfterCreate)
{
CHECK_EQUAL_C_BITS(_BV(ADPS2)|_BV(ADPS1), ADCSRA, _BV(ADPS2) | _BV(ADPS1)|_BV(ADPS0));
}
TEST(TEST_HAL, get_voltageCalledWithCh15SetsMuxTo100111)
{
hal_get_voltage(15);
CHECK_EQUAL_C_BITS(_BV(MUX5), ADCSRB, _BV(MUX5));
CHECK_EQUAL_C_BITS(_BV(MUX2) | _BV(MUX1) | _BV(MUX0), ADMUX,
_BV(MUX4) | _BV(MUX3) | _BV(MUX2) | _BV(MUX1) | _BV(MUX0));
}

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Test cases can check that bits in registers are set and read in right order
and return values can be controlled
TEST(TEST_HAL, get_voltageCalledSetsAndWaitsForADSCtoClear)
{
mock().expectOneCall("mock_set_bit").withPointerParameter("reg",
&ADCSRA).withIntParameter("bit_no", ADSC);
mock().expectNCalls(5,"mock_read_bit").withPointerParameter("reg",
&ADCSRA).withIntParameter("bit_no", ADSC).andReturnValue(_BV(ADSC));
mock().expectOneCall("mock_read_bit")
.withPointerParameter("reg"&ADCSRA).withIntParameter("bit_no", ADSC).andReturnValue(0);
hal_get_voltage(0);
}

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The Mocks are injected via dependency injection:
// ---------------------------------------------------------------------------------------
uint8_t mock_read_bit(volatile uint8_t * reg, uint8_t bit_no)
{
mock().actualCall("mock_read_bit").withPointerParameter("reg", (void *)reg)
.withIntParameter("bit_no", bit_no);
return mock().returnIntValueOrDefault(0);
}
// --------------------------------------------------------------------------------------
void mock_set_bit(volatile uint8_t * reg, uint8_t bit_no)
{
// Production code function called
set_bit(reg, bit_no);
mock().actualCall("mock_set_bit").withPointerParameter("reg", (void *)reg)
.withIntParameter("bit_no", bit_no);
}

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Test that calculations are correct in driver, faking hardware registers
TEST(TEST_HAL, get_voltageReturnsFullVRef)
{
// Given
ADCL = 0b11111111;
ADCH = 0b00000011;
// When
float result = hal_get_voltage(0);
// Then
float expected = ((ADCH << 8) + ADCL) * _V_REF / 1024;
CHECK_EQUAL_C_REAL(expected, result, 0.001);
}

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Faking Interrupts
The Interrupt Service Routine (ISR ) in the production code:
ISR(INT0_vect)
{
PORTA = 0x55;
}
The macro that fakes it:
#define ISR(vector, ...) void ISR_##vector(void)
In the test cases the ISR is now turned into a normal function with the following
signature:
void ISR_INT0_vect(void)

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Faking Interrupts
The Test that check that the ISR is doing what it is supposed to do
TEST(TEST_HAL, INT0ISRIsSettingPORTAto0x55)
{
ISR_INT0_vect(); // Fake INT0 Interrupt
CHECK_EQUAL_C_INT(0x55, PORTA);
}

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What Test-cases to write:
Take a look at James W. Grenning’s ZOMBIES:
– Z – Zero
– O – One
– M – Many (or More complex)
– B – Boundary Behaviours
– I – Interface definition
– E – Exercise Exceptional behaviour
– S – Simple Scenarios, Simple Solutions

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Pros:
– Production code can be developed at Host-computer
– Use all Host-computer tools and Debugger facilities
– Less errors and failures when moving to target computer
– Develop without the target hardware
Cons:
– It takes time to figure out how to get rid of the hardware dependencies in the
target tool-chain (One time only investment)
– Real-time aspects can’t be tested on the Host-computer

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Conclusion
– It is hard to develop low-level and hardware near software
– Invest time in setting up your tools and environment
(one time investment per platform)
– Use all the principles that we know from high-level development
(OOD/P)
– Document using UML and/or SysML
– TTD is possible and not very hard when tools are setup
– Software is easy and safe to maintain if it is well designed and the test
suite is up-to-date

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References
– CppUTest (open source): http://cpputest.github.io/index.html
– James W. Grenning, 2011: Test Driven Development for Embedded C, 1st Edition,
ISBN-13: 978-1934356623, ISBN-10: 9781934356623
– Axel Schreiner : Object-oriented Programming in ANSI-C
– Beck, K., 2002 Test Driven Development: By Example, ISBN-10: 9780321146533
ISBN-13: 978-0321146533
– Robert C. Martin, 2002: Agile Software Development, Principles, Patterns, and
Practices, ISBN10 0135974445 ISBN13 9780135974445
– James W. Grenning’s ZOMBIES: http://blog.wingman-sw.com/archives/677

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