2023-12-09 05:35 AM - edited 2023-12-09 06:03 AM
Hi Guys,
This is driving me mad!
So this works perfectly echoing characters via uart8:
int ch = 'A';
while (1)
{
HAL_UART_Transmit(&huart8, (uint8_t *)&ch, 1, 0xFFFF);
HAL_UART_Receive(&huart8, (uint8_t *)&ch, 1, 0xFFFF);
}
Now if I have getchar and put char implementations:
#define PUTCHAR_PROTOTYPE int __io_putchar(int ch)
#define GETCHAR_PROTOTYPE int __io_getchar(void)
PUTCHAR_PROTOTYPE
{
HAL_UART_Transmit(&huart8, (uint8_t *)&ch, 1, 0xFFFF);
return ch;
}
GETCHAR_PROTOTYPE
{
uint8_t ch;
__HAL_UART_CLEAR_OREFLAG(&huart8);
HAL_UART_Receive(&huart8, &ch, 1, 0xFFFF);
return ch;
}
The following does not work, we do not get anything received and get stuck in UART_WaitOnFlagUntilTimeout() called from HAL_UART_Receive() from __io_getchar():
while (1)
{
HAL_UART_Transmit(&huart8, (uint8_t *)&ch, 1, 0xFFFF);
ch = getchar();
}
However if I directly call __io_getchar() everything works perfectly, UART data is received:
while (1)
{
HAL_UART_Transmit(&huart8, (uint8_t *)&ch, 1, 0xFFFF);
ch = __io_getchar();
}
Has anyone any idea why __io_getchar() called directly is working and when called indirectly it isn't, no UART data?
Cheers
Andy
Solved! Go to Solution.
2023-12-09 06:34 AM
With this code:
We get this after one getchar() call:
You can set the input to unbuffered to get only a single call.
setvbuf(stdin, NULL, _IONBF, 0);
2023-12-09 06:12 AM
Input is buffered, so when you request a char, it reads a large number of inputs (in this case, 1024), before giving you the one you requested.
2023-12-09 06:34 AM
With this code:
We get this after one getchar() call:
You can set the input to unbuffered to get only a single call.
setvbuf(stdin, NULL, _IONBF, 0);
2023-12-09 07:51 AM
2024-04-04 07:14 AM
Pleas, share with us where this:
setvbuf(stdin, NULL, _IONBF, 0);
is documented. I would like to know before I get bit by some other "Gotch-yah" like this one.
Thanks.
Clyde