Posted on August 05, 2011 at 12:26The GPIO struct is defined but it is not initialized before it is used in main. Everything works but I am stuck with trying to find a value that I can use in GPIO_Init. GPIOx->CR2 is OR'd with another value and I don't know where to get the initial value GPIOx->CR2. The only thing I can think is that a random number is in that address.
This is in the given program that comes with the firmware. I am new to C and this is probably a simple problem.
Thanks,
Chris
In the main function that comes with the Discovery microcontroller. The first thing that main does is to call GPIO_Init. I have included it here.
void GPIO_Init(GPIO_TypeDef* GPIOx,
uint8_t GPIO_Pin,
GPIO_Mode_TypeDef GPIO_Mode)
{
/*----------------------*/
/* Check the parameters */
/*----------------------*/
assert_param(IS_GPIO_MODE(GPIO_Mode));
assert_param(IS_GPIO_PIN(GPIO_Pin));
/* Reset crresponding bit to GPIO_Pin in CR2 register */
GPIOx->CR2 &= (uint8_t)(~(GPIO_Pin)); /*-----------------------------*/
/* Input/Output mode selection */
/*-----------------------------*/
if ((((uint8_t)(GPIO_Mode)) & (uint8_t)0x80) != (uint8_t)0x00) /* Output mode */
{
if ((((uint8_t)(GPIO_Mode)) & (uint8_t)0x10) != (uint8_t)0x00) /* High level */
{
GPIOx->ODR |= GPIO_Pin;
} else /* Low level */
{
GPIOx->ODR &= (uint8_t)(~(GPIO_Pin));
}
/* Set Output mode */
GPIOx->DDR |= GPIO_Pin;
} else /* Input mode */
{
/* Set Input mode */
GPIOx->DDR &= (uint8_t)(~(GPIO_Pin));
}
I think you can see that GPIOx->CR2 and GPIOx->ODR and GPIOx->DDR are being used to set bits.(Outlined in RED) My thinking is that they are not initialized by the function GPIO_Init yet so any number that happens to be in that address could be used.
I am a beginner in both uC's and C. Thanks for your help.
Chris
#initialize-a-structure #memory-mapped-peripherals
