Raspberry Pi Pico (RP2040) - wrong order of printf arguments?

Question

I've just started working with RPi Pico (RP2040), and I tried the following simple program:

#include <stdio.h>
#include "pico/stdlib.h"
volatile int chars_rxed = 0;
int main() {
    stdio_init_all();
    while (true) {
        printf("%d: chrx %d\n", to_us_since_boot(get_absolute_time()), chars_rxed );
        sleep_ms(1000);
    }
    return 0;
}

I'm compiling on MINGW64 under Windows. Program compiles fine, then I plug the Pico pressing the BOOTSEL button, I get the "drive", and I copy the .uf2 result there.

Then, when the Pico reboots, I connect to its USB Serial port using tio - and this is the printout I get:

$  tio --baudrate 115200 --databits 8 --flow none --stopbits 1 --parity none /dev/ttyS6
[tio 13:04:18] tio v1.32
[tio 13:04:18] Press ctrl-t q to quit
[tio 13:04:18] Connected
0: chrx 5005043
0: chrx 6005262
0: chrx 7005426
0: chrx 8005621
0: chrx 9005778

Considering the chars_rxed is always 0 in the code, it seems the printout reverses the order of arguments: so instead of printing to_us_since_boot(get_absolute_time()), chars_rxed, it prints chars_rxed, to_us_since_boot(get_absolute_time()).

But WHY? I've never seen this kind of a problem before ...

How can I get printf for Pico to print out the arguments as specified?

score 1 · Answer 1 · answered Apr 01 '22 at 11:18

I think I got it - turns out, to_us_since_boot returns uint64_t, and thus the %d string format specifier is inappropriate for it.

Therefore, I have to use a different format specifier, and I decided on PRIu64 from inttypes.h:

#include <inttypes.h> //PRIu64
#include <stdio.h>
#include "pico/stdlib.h"
volatile int chars_rxed = 0;
int main() {
    stdio_init_all();
    while (true) {
        printf("%"PRIu64 ": chrx %d\n", to_us_since_boot(get_absolute_time()), chars_rxed );
        sleep_ms(1000);
    }
    return 0;
}

This now prints the expected results:

$  tio --baudrate 115200 --databits 8 --flow none --stopbits 1 --parity none /dev/ttyS6
[tio 13:15:56] tio v1.32
[tio 13:15:56] Press ctrl-t q to quit
[tio 13:15:56] Connected
4005136: chrx 0
5005345: chrx 0
6005522: chrx 0
7005689: chrx 0
8005847: chrx 0

Raspberry Pi Pico (RP2040) - wrong order of printf arguments?

1 Answers1