Description
Hello,
Using the Cargo config as below,
...
[target.thumbv7m-none-eabi]
runner = "qemu-system-arm -cpu cortex-m3 -machine lm3s6965evb -nographic -semihosting-config enable=on,target=native -kernel"
[build]
target = "thumbv7m-none-eabi" # Cortex-M3
...
I tested running the below program using QEMU.
#![no_std]
#![no_main]
extern crate panic_halt;
use cortex_m::asm;
use cortex_m_rt::entry;
use cortex_m::peripheral::syst::SystClkSource;
use cortex_m::peripheral::SYST;
use cortex_m_semihosting::{debug, hprintln};
#[entry]
fn main() -> ! {
let p = cortex_m::Peripherals::take().unwrap();
let mut syst = p.SYST;
syst.set_clock_source(SystClkSource::Core);
syst.set_reload(SYST::get_ticks_per_10ms() * 1000); // Works strange in QEMU?
syst.enable_counter();
hprintln!(
"{} ticks = 10 millisecond", SYST::get_ticks_per_10ms()
).unwrap();
let mut seconds: usize = 0;
loop {
// busy wait until the timer wraps around
while !syst.has_wrapped() {}
seconds += 1;
hprintln!("{} seconds passed", seconds).unwrap(); // prints every second!
}
}I checked that fn get_ticks_per_10ms always returns 10_000 in my program.
Since I set called the set_reload function with an argument of get_ticks_per_10ms() * 1_000,
I expected the program to print out to the console every 10 seconds (since ticks_per_10ms * 1_000 == ticks_per_10seconds).
However, the program prints out to the console every 1 second.
I tried changing the argument fed to set_reload(), and it seems like the get_ticks_per_10ms() is behaving like get_ticks_per_1ms().
Unfortunately, I do not have an actual cortex-m device to test this behavior.
I'm currently not sure whether this is an issue with the api of the cortex-m crate, or QEMU.
If this is an issue with the cortex-m crate, maybe the function name of fn get_ticks_per_10ms should be changed to fn get_ticks_per_1ms.
Thank you for reading 😄