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Niklas Lundberg
rtic_f4xx_nucleo
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master to 3ffc19801ddecd289507fd1fb1444cc01cd10d61
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inaule-6/rtic_f4xx_nucleo
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pln/rtic_f4xx_nucleo
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pln/rtic_f4xx_nucleo
ironedde/rtic_f4xx_nucleo
inaule-6/rtic_f4xx_nucleo
rubenasplund/rtic_f4xx_nucleo
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Commits on Source (3)
Finished exercises in main
· 1b747d6c
Blinningjr
authored
4 years ago
1b747d6c
rtt_timing c
· dcadd8fe
Blinningjr
authored
4 years ago
dcadd8fe
rtt_timing D
· 3ffc1980
Blinningjr
authored
4 years ago
3ffc1980
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3 changed files
examples/rtt_timing.rs
+36
-0
36 additions, 0 deletions
examples/rtt_timing.rs
rtt_timing.objdump
+2308
-0
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rtt_timing.objdump
src/main.rs
+90
-5
90 additions, 5 deletions
src/main.rs
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2434 additions
and
5 deletions
examples/rtt_timing.rs
View file @
3ffc1980
...
...
@@ -60,37 +60,57 @@ fn timed_loop() -> (u32, u32) {
// ------------------------------------------------------------------------
// Exercises:
//
// start 2987, end 4793139, diff 4790152
//
// A.1) What is the cycle count for the loop?
// > cargo run --example rtt_timing
//
// [Your answer here]
// 2987
//
// A.2) How many cycles per iteration?
//
// [Your answer here]
// 4790152
//
// A.3) Why do we need a wrapping subtraction?
//
// [Your answer here]
// If end value has wrapped around then start > end. Thus we need to wrap around when we subtract so we get the correct difference value.
//
// ------------------------------------------------------------------------
// Now try a release (optimized build, see `Cargo.toml` for build options).
// B.1) What is the cycle count for the loop?
// > cargo run --example rtt_timing --release
//
// start 30305915, end 30375916, diff 70001
//
// [Your answer here]
// 30305915
//
// B.2) How many cycles per iteration?
//
// [Your answer here]
// 70001
//
// What is the speedup (A/B)?
//
// [Your answer here]
// 4790152 / 70001 = 68.4297652891
//
//
// Why do you think it differs that much?
//
// [Your answer here]
// I think that the optimizer removed the for loop:
// for _ in 0..10000 {
// asm::nop();
// }
// Thus the end variable is set right after the start variable. This makes the time difference very
// small. But it is not near 10000 time faster because the function DWT::get_cycle_count() is much
// slower at getting the cycle count then it is to run one iteration of the loop.
//
//
//
// ------------------------------------------------------------------------
// In the loop there is just a single assembly instruction (nop).
...
...
@@ -112,15 +132,20 @@ fn timed_loop() -> (u32, u32) {
// C.1) What is the cycle count for the loop?
// > cargo run --example rtt_timing --release --features nightly
//
// start 1356808538, end 1356848539, diff 40001
//
// [Your answer here]
// 1356808538
//
// C.2) How many cycles per iteration?
//
// [Your answer here]
// 40001
//
// What is the speedup (A/C)?
//
// [Your answer here]
// 4790152 / 40001 = 119.75080623
//
// ------------------------------------------------------------------------
// D) Now lets have a closer look at the generated assembly.
...
...
@@ -131,6 +156,17 @@ fn timed_loop() -> (u32, u32) {
//
// [Assembly for function `timed_loop` here]
//
// 08000232 <timed_loop>:
// 8000232: movw r1, #4100
// 8000236: movw r2, #10000
// 800023a: movt r1, #57344
// 800023e: ldr r0, [r1]
// 8000240: subs r2, #1
// 8000242: nop
// 8000244: bne #-8 <timed_loop+0xe>
// 8000246: ldr r1, [r1]
// 8000248: bx lr
//
// Locate the loop body, and verify that it makes sense
// based on the information from the technical documentation:
//
...
...
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rtt_timing.objdump
0 → 100644
View file @
3ffc1980
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src/main.rs
View file @
3ffc1980
...
...
@@ -21,10 +21,10 @@ const APP: () = {
#[idle]
fn
idle
(
_cx
:
idle
::
Context
)
->
!
{
rprintln!
(
"idle"
);
//
panic!("panic");
loop
{
continue
;
}
panic!
(
"panic"
);
//
loop {
//
continue;
//
}
}
};
...
...
@@ -51,6 +51,7 @@ const APP: () = {
// at /home/pln/.cargo/registry/src/github.com-1ecc6299db9ec823/cortex-m-rt-0.6.13/src/lib.rs:526
//
// Make sure you got the expected output
// Awnser: Yes, got the expected output.
//
// C) Panic tracing
// Rust is designed for reliability, with the aim to deliver memory safety
...
...
@@ -64,6 +65,30 @@ const APP: () = {
// What is the output?
//
// [Your answer here]
// Compiling app v0.1.0 (/home/niklas/Desktop/D7020E/rtic_f4xx_nucleo)
// error: unreachable expression
// --> src/main.rs:25:9
// |
// 24 | panic!("panic");
// | ---------------- any code following this expression is unreachable
// 25 | / loop {
// 26 | | continue;
// 27 | | }
// | |_________^ unreachable expression
// |
// note: the lint level is defined here
// --> src/main.rs:4:9
// |
// 4 | #![deny(warnings)]
// | ^^^^^^^^
// = note: `#[deny(unreachable_code)]` implied by `#[deny(warnings)]`
//
// error: aborting due to previous error
//
// error: could not compile `app`
//
// To learn more, run the command again with --verbose.
//
//
// D) Panic halt
// Tracing is nice during development, but requires a debugger attached
...
...
@@ -77,12 +102,37 @@ const APP: () = {
// What is the output?
//
// [Your answer here]
// Compiling app v0.1.0 (/home/niklas/Desktop/D7020E/rtic_f4xx_nucleo)
// Finished dev [unoptimized + debuginfo] target(s) in 0.68s
// Running `probe-run --chip STM32F411RETx target/thumbv7em-none-eabi/debug/app`
// (HOST) INFO flashing program (10.53 KiB)
// (HOST) INFO success!
//────────────────────────────────────────────────────────────────────────────────
//init
//idle
//
//
// Now press Ctrl-C
//
// What is the output?
//
// [Your answer here]
//^Cstack backtrace:
// 0: core::sync::atomic::compiler_fence
// at /home/niklas/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/sync/atomic.rs:2644
// 1: rust_begin_unwind
// at /home/niklas/.cargo/registry/src/github.com-1ecc6299db9ec823/panic-halt-0.2.0/src/lib.rs:33
// 2: core::panicking::panic_fmt
// at /rustc/7eac88abb2e57e752f3302f02be5f3ce3d7adfb4/library/core/src/panicking.rs:85
// 3: core::panicking::panic
// at /rustc/7eac88abb2e57e752f3302f02be5f3ce3d7adfb4/library/core/src/panicking.rs:50
// 4: app::idle
// at src/main.rs:24
// 5: main
// at src/main.rs:13
// 6: Reset
// at /home/niklas/.cargo/registry/src/github.com-1ecc6299db9ec823/cortex-m-rt-0.6.13/src/lib.rs:526
//
//
// E) Find the source
// Figure out how to find the source of `panic_halt`, and look at the implementation.
...
...
@@ -92,3 +142,38 @@ const APP: () = {
//
// Paste the implementation here
// [Your answer here]
////! Set the panicking behavior to halt
////!
////! This crate contains an implementation of `panic_fmt` that simply halt in an infinite loop.
////!
////! # Usage
////!
////! ``` ignore
////! #![no_std]
////!
////! extern crate panic_halt;
////!
////! fn main() {
////! panic!("argument is ignored");
////! }
////! ```
////!
////! # Breakable symbols
////!
////! With the panic handler being `#[inline(never)]` the symbol `rust_begin_unwind` will be
////! available to place a breakpoint on to halt when a panic is happening.
//
//#![deny(missing_docs)]
//#![deny(warnings)]
//#![no_std]
//
//use core::panic::PanicInfo;
//use core::sync::atomic::{self, Ordering};
//
//#[inline(never)]
//#[panic_handler]
//fn panic(_info: &PanicInfo) -> ! {
// loop {
// atomic::compiler_fence(Ordering::SeqCst);
// }
//}
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