Pointer to peripheral hardware as template parameter - c++

Question

I want to access STM32F0 peripheral register through C++ templates. A GPIO Port is defined as follows by vendor header file:
excerpt stm32f0xx.h
#define __IO volatile //!< Defines 'read / write' permissions
typedef struct
{
__IO uint32_t MODER;
__IO uint16_t OTYPER;
uint16_t RESERVED0;
__IO uint32_t OSPEEDR;
__IO uint32_t PUPDR;
__IO uint16_t IDR;
uint16_t RESERVED1;
__IO uint16_t ODR;
uint16_t RESERVED2;
__IO uint32_t BSRR;
__IO uint32_t LCKR;
__IO uint32_t AFR[2];
__IO uint16_t BRR;
uint16_t RESERVED3;
} GPIO_TypeDef;
#define PERIPH_BASE ((uint32_t)0x40000000)
#define AHB2PERIPH_BASE (PERIPH_BASE + 0x08000000)
#define GPIOA_BASE (AHB2PERIPH_BASE + 0x00000000)
#define GPIOA ((GPIO_TypeDef *) GPIOA_BASE)
I created a template class for output handling.
main.cpp:
template <uintptr_t port, uint8_t pin>
class Output {
public:
static void set() {
GPIO_TypeDef *castedPort = reinterpret_cast<GPIO_TypeDef *>(port);
castedPort->ODR = (1 << pin);
}
};
int main(void)
{
Output<GPIOA_BASE, 5>::set();
while(1)
{
}
}
This code runs fine, if I compile it with launchpad g++ for arm. But I want to test my code
with GoogleTest, so I made a test for it and tried to compile it.
intArgument.cpp:
#include "gtest/gtest.h"
typedef struct {
/* see above definition */
} GPIO_TypeDef;
uint32_t gpioa[10] = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
template <uintptr_t port, int pin>
class Output {
public:
static void set() {
GPIO_TypeDef * castedPort = reinterpret_cast<GPIO_TypeDef *>(port);
castedPort->ODR = (1 << pin);
}
};
TEST(OutputTest, OutputDataRegisterWritten) {
Output<gpioa, 5>::set();
GPIO_TypeDef * port = reinterpret_cast<GPIO_TypeDef *>(gpioa);
EXPECT_EQ((1 << 5), port->ODR);
}
int main(int argc, char **argv) {
::testing::InitGoogleTest(&argc, argv);
return RUN_ALL_TESTS();
}
But now compile fails. A cast to a int via reinterpret_cast is not allowed, because then it is no more a constant expression.
fabian#ubuntu:~/workspace/stackOverflowQuestion$ g++ -std=c++11 intArgument.cpp -lgtest -pthread -o intptrArgument.out
intArgument.cpp: In member function ‘virtual void OutputTest_OutputDataRegisterWritten_Test::TestBody()’:
intArgument.cpp:23:18: error: conversion from ‘uint32_t* {aka unsigned int*}’ to ‘long unsigned int’ not considered for non-type template argument
Output<gpioa, 5>::set();
^
intArgument.cpp:23:18: error: could not convert template argument ‘gpioa’ to ‘long unsigned int’
intArgument.cpp:23:26: error: invalid type in declaration before ‘;’ token
Output<gpioa, 5>::set();
So i tried to change type of port to GPIO_TypeDef *.
pointerArgument.cpp:
typedef struct {
/* see above definition */
} GPIO_TypeDef;
GPIO_TypeDef gpioa;
// using GPIO_TypeDef * as template argument
template <GPIO_TypeDef * port, int pin>
class Output {
public:
static void set() {
port->ODR = (1 << pin);
}
};
TEST(OutputTest, OutputDataRegisterWritten) {
Output<&gpioa, 5>::set();
EXPECT_EQ((1 << 5), gpioa.ODR);
}
int main(int argc, char **argv) {
::testing::InitGoogleTest(&argc, argv);
return RUN_ALL_TESTS();
}
It compiled and test is passed.
fabian#ubuntu:~/workspace/stackOverflowQuestion$ g++ -std=c++11 pointerArgument.cpp -lgtest -pthread -o pointerArgument.out
fabian#ubuntu:~/workspace/stackOverflowQuestion$ ./test.out
[==========] Running 1 test from 1 test case.
[----------] Global test environment set-up.
[----------] 1 test from OutputTest
[ RUN ] OutputTest.OutputDataRegisterWritten
[ OK ] OutputTest.OutputDataRegisterWritten (0 ms)
[----------] 1 test from OutputTest (1 ms total)
[----------] Global test environment tear-down
[==========] 1 test from 1 test case ran. (1 ms total)
[ PASSED ] 1 test.
But using this approach is failing for the arm compiler:
main.cpp
template <GPIO_TypeDef * port, uint8_t pin>
class Output {
public:
static void set() {
port->ODR = (1 << pin);
}
};
int main(void)
{
Output<GPIOA, 5>::set();
while(1)
{
}
}
compiler error:
[cc] main.cpp:13:17: error: '1207959552u' is not a valid template argument for 'GPIO_TypeDef*' because it is not the address of a variable
[cc] main.cpp:13:25: error: invalid type in declaration before ';' token
I understand both errors, but is there any way to get this work? I searched for compiler flags, but did not find
any, that might change this behaviour. A #define TESTING combined with #ifdef/#ifndef might work, but I dont
like it, because then tested code differs from produced code. Perhaps there is a nicer solution?
Used Compilers:
g++ (i686-posix-dwarf-rev3, Built by MinGW-W64 project), 4.9-2014q4 by Launchpad for STM32F0XX
g++ (Ubuntu 4.9.2-0ubuntu1~14.04) 4.9.2 for Testing

Answer 1

With linker flag Wl,section-start you can define the start address of a specified section. So first I forced my register mocks to be in a own section:
GPIO_TypeDef gpioa __attribute__((section(".myTestRegisters")));
GPIO_TypeDef gpiob __attribute__((section(".myTestRegisters")));
Also I defined const uintptr_t address values for section start and each register.
const uintptr_t myTestRegisterSectionAddress = 0x8000000;
const uintptr_t gpioaAddress = myTestRegisterSectionAddress;
const uintptr_t gpiobAddress = myTestRegisterSectionAddress + sizeof(GPIO_TypeDef);
These values I can use as template parameter.
template <uintptr_t port, int pin>
class Output {
public:
static void set() {
GPIO_TypeDef * castedPort = reinterpret_cast<GPIO_TypeDef *>(port);
castedPort->ODR = (1 << pin);
}
};
TEST(OutputTest, OutputDataRegisterWritten) {
Output<gpioaAddress, 5>::set();
EXPECT_EQ(1 << 5, gpioa.ODR);
Output<gpiobAddress, 10>::set();
EXPECT_EQ(1 << 10, gpiob.ODR);
}
int main(int argc, char **argv) {
::testing::InitGoogleTest(&argc, argv);
return RUN_ALL_TESTS();
}
To force a start address for a section you can use Wl,-section-start=.{sectionName}={startAddress}.
So in my case I use:
g++ intArgument.cpp -std=c++11 -g -o intArgument.out -lgtest -pthread -Wl,-section-start=.myTestRegisters=0x8000000
Running application results in:
fabian#ubuntu:~/workspace/stackOverflowQuestion$ ./intArgument.out
[==========] Running 1 test from 1 test case.
[----------] Global test environment set-up.
[----------] 1 test from OutputTest
[ RUN ] OutputTest.OutputDataRegisterWritten
[ OK ] OutputTest.OutputDataRegisterWritten (0 ms)
[----------] 1 test from OutputTest (0 ms total)
[----------] Global test environment tear-down
[==========] 1 test from 1 test case ran. (0 ms total)
[ PASSED ] 1 test.
And a objdump shows following information:
fabian#ubuntu:~/workspace/stackOverflowQuestion$ objdump -S -j .myTestRegisters intArgument.out
intArgument.out: file format elf64-x86-64
Disassembly of section .myTestRegisters:
0000000008000000 <gpioa>:
...
000000000800000c <gpiob>:
This works not with optimizations because the elements can be swapped.