C Atmega328P String to Int Conversion blocks RX Interrupt - c

Question

i've used an Atmega328P µC to get a string over UART and convert it to an int.
I've tried to use atoi() function or sscanf() to convert it but they are taking to long to convert so that they are blocking the interrupt.
If I stop converting and just receiving over UART all symbols are transmitted but if I convert after receiving some characters of transmission are missed.
Is there any way to speed up conversion to stop blocking RX interrupt?

Answer 1

If you need to convert multicharacter numbers to integer you need to use buffer. There example of cycle buffer uses:
#define BUF_LEN 128
#define BUF_MSK (BUF_LEN-1)
uint8_t buf[BUF_LEN], b_in = 0, b_out = 0;
void usart_irq_handler(void)
{
buf[b_in&BUF_MSK] = USART_DATA_REG;
b_in++;
}
int main(void)
{
uint8_t tmp;
while (b_in!=b_out) {
tmp = buf[b_out&BUF_MSK];
b_out++;
// parse here
}
}
If you need to convert single character numbers you may not use buffer (but if USART frequency not much less than CPU frequency it's not recommended). For ASCII encoded received characters each number will have values 0x30..0x39. If received characters encoded with another charset you need refer to their tables.
uint8_t num = USART_DATA_REG - 0x30;
if (num >= 0 && num <= 9) {
// is number
}
EDIT 1 [due to new information from OP] For convert decimal number from string to integer I use this function:
uint32_t parse_num(uint8_t * ptr)
{
uint32_t res = (uint32_t)0x0;
uint8_t chr = 0x0, pchr = 0xA;
while (*ptr != (uint8_t)0x0) {
chr = (uint8_t)(*ptr - (uint8_t)0x30);
if (chr < 0xA) {
res *= (uint32_t) 0xA;
res += (uint32_t) chr;
} else {
if (pchr < 0xA) break;
}
pchr = chr;
ptr++;
}
return res;
}
It skip non-numbers chars and convert first founded number, but doesn't return final position of parse buffer. You can modify it as you need.
EDIT 2 [due to chat with OP] about good approach to processor time management:
Pictures below (from this answer) illustrate normal processor timing in program:
So, the smaller the interrupt handler time - the more likely success of the other handlers, and more time to perform main process.
By increasing of MCU clock is reduced run time code and increases idle time.
By decreasing of periferal clock is reduced frequency of interrupts by perifery and increases idle time.
In conclusion idle time must be used for power save.

Answer 2

Yes, the function runs in main loop and copies the chars out of buffer which is filled in the interrupt routine. After detecting the \n in string, it converts the string into values using sscanf or char by char. I've first used a very slow baud rate and then a very fast one. There are also two more interrupt routines (for timing of 100us and one for a pwm driver). I've tried to take out code of these routines to speed them up and it was successful. Now the interrupt routine gets every character of the uart transmission. Now I am implementing an algorithm to convert the strings to values without using sscanf because of performance issues. Using the algorithm of imbearr with -0x30 should work properly.