Prevent underflow when calling delay(n) with n<2

[ovidiusabou]

Calling delay(1) causes a very long wait (freeze) otherwise.
86cd463 introduced this behaviour by
changing the cycle count from n / 4 + 1 to n / 2 which forces an
underflow when n<2.

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @thalesfragoso (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

Please see the contribution instructions for more information.

[jonas-schievink]

Change looks good to me, thanks! Can you add a short comment explaining why we add 1?

[jonas-schievink]

Also, run cargo xtask assemble to update the blobs, then CI should pass

[ovidiusabou]

I ran cargo xtask assemble but CI still doesn't pass.

[jonas-schievink]

If I run it locally it still changes the archives. What OS are you on?

[ovidiusabou]

Mac OS

[ovidiusabou]

~/Projects/cortex-m fix-delay-underflow ❯ git status
On branch fix-delay-underflow
Your branch is up to date with 'origin/fix-delay-underflow'.

nothing to commit, working tree clean
~/Projects/cortex-m fix-delay-underflow ❯ cargo xtask assemble
    Finished dev [unoptimized + debuginfo] target(s) in 0.01s
     Running `target/debug/xtask assemble`
info: component 'rust-std' for target 'thumbv6m-none-eabi' is up to date
info: component 'rust-std' for target 'thumbv7m-none-eabi' is up to date
info: component 'rust-std' for target 'thumbv7em-none-eabi' is up to date
info: component 'rust-std' for target 'thumbv7em-none-eabihf' is up to date
info: component 'rust-std' for target 'thumbv8m.base-none-eabi' is up to date
info: component 'rust-std' for target 'thumbv8m.main-none-eabi' is up to date
info: component 'rust-std' for target 'thumbv8m.main-none-eabihf' is up to date
building artifacts for thumbv6m-none-eabi
"rustc" "+nightly-2020-08-26" "--target" "thumbv6m-none-eabi" "-g" "-O" "-Clto=yes" "-Cforce-frame-pointers=no" "--remap-path-prefix" "/Users/ovidiu/Projects/cortex-m=." "--emit=obj" "-o" "bin/thumbv6m-none-eabi.o" "asm/lib.rs"
"rustc" "+nightly-2020-08-26" "--target" "thumbv6m-none-eabi" "-g" "-O" "-Clto=yes" "-Cforce-frame-pointers=no" "--remap-path-prefix" "/Users/ovidiu/Projects/cortex-m=." "--emit=obj" "-Clinker-plugin-lto" "-o" "bin/thumbv6m-none-eabi-lto.o" "asm/lib.rs"
building artifacts for thumbv7m-none-eabi
"rustc" "+nightly-2020-08-26" "--target" "thumbv7m-none-eabi" "--cfg=armv7m" "-g" "-O" "-Clto=yes" "-Cforce-frame-pointers=no" "--remap-path-prefix" "/Users/ovidiu/Projects/cortex-m=." "--emit=obj" "-o" "bin/thumbv7m-none-eabi.o" "asm/lib.rs"
"rustc" "+nightly-2020-08-26" "--target" "thumbv7m-none-eabi" "--cfg=armv7m" "-g" "-O" "-Clto=yes" "-Cforce-frame-pointers=no" "--remap-path-prefix" "/Users/ovidiu/Projects/cortex-m=." "--emit=obj" "-Clinker-plugin-lto" "-o" "bin/thumbv7m-none-eabi-lto.o" "asm/lib.rs"
building artifacts for thumbv7em-none-eabi
"rustc" "+nightly-2020-08-26" "--target" "thumbv7em-none-eabi" "--cfg=armv7m" "--cfg=armv7em" "-g" "-O" "-Clto=yes" "-Cforce-frame-pointers=no" "--remap-path-prefix" "/Users/ovidiu/Projects/cortex-m=." "--emit=obj" "-o" "bin/thumbv7em-none-eabi.o" "asm/lib.rs"
"rustc" "+nightly-2020-08-26" "--target" "thumbv7em-none-eabi" "--cfg=armv7m" "--cfg=armv7em" "-g" "-O" "-Clto=yes" "-Cforce-frame-pointers=no" "--remap-path-prefix" "/Users/ovidiu/Projects/cortex-m=." "--emit=obj" "-Clinker-plugin-lto" "-o" "bin/thumbv7em-none-eabi-lto.o" "asm/lib.rs"
building artifacts for thumbv7em-none-eabihf
"rustc" "+nightly-2020-08-26" "--target" "thumbv7em-none-eabihf" "--cfg=armv7m" "--cfg=armv7em" "--cfg=has_fpu" "-g" "-O" "-Clto=yes" "-Cforce-frame-pointers=no" "--remap-path-prefix" "/Users/ovidiu/Projects/cortex-m=." "--emit=obj" "-o" "bin/thumbv7em-none-eabihf.o" "asm/lib.rs"
"rustc" "+nightly-2020-08-26" "--target" "thumbv7em-none-eabihf" "--cfg=armv7m" "--cfg=armv7em" "--cfg=has_fpu" "-g" "-O" "-Clto=yes" "-Cforce-frame-pointers=no" "--remap-path-prefix" "/Users/ovidiu/Projects/cortex-m=." "--emit=obj" "-Clinker-plugin-lto" "-o" "bin/thumbv7em-none-eabihf-lto.o" "asm/lib.rs"
building artifacts for thumbv8m.base-none-eabi
"rustc" "+nightly-2020-08-26" "--target" "thumbv8m.base-none-eabi" "--cfg=armv8m" "--cfg=armv8m_base" "-g" "-O" "-Clto=yes" "-Cforce-frame-pointers=no" "--remap-path-prefix" "/Users/ovidiu/Projects/cortex-m=." "--emit=obj" "-o" "bin/thumbv8m.base-none-eabi.o" "asm/lib.rs"
"rustc" "+nightly-2020-08-26" "--target" "thumbv8m.base-none-eabi" "--cfg=armv8m" "--cfg=armv8m_base" "-g" "-O" "-Clto=yes" "-Cforce-frame-pointers=no" "--remap-path-prefix" "/Users/ovidiu/Projects/cortex-m=." "--emit=obj" "-Clinker-plugin-lto" "-o" "bin/thumbv8m.base-none-eabi-lto.o" "asm/lib.rs"
building artifacts for thumbv8m.main-none-eabi
"rustc" "+nightly-2020-08-26" "--target" "thumbv8m.main-none-eabi" "--cfg=armv7m" "--cfg=armv8m" "--cfg=armv8m_main" "-g" "-O" "-Clto=yes" "-Cforce-frame-pointers=no" "--remap-path-prefix" "/Users/ovidiu/Projects/cortex-m=." "--emit=obj" "-o" "bin/thumbv8m.main-none-eabi.o" "asm/lib.rs"
"rustc" "+nightly-2020-08-26" "--target" "thumbv8m.main-none-eabi" "--cfg=armv7m" "--cfg=armv8m" "--cfg=armv8m_main" "-g" "-O" "-Clto=yes" "-Cforce-frame-pointers=no" "--remap-path-prefix" "/Users/ovidiu/Projects/cortex-m=." "--emit=obj" "-Clinker-plugin-lto" "-o" "bin/thumbv8m.main-none-eabi-lto.o" "asm/lib.rs"
building artifacts for thumbv8m.main-none-eabihf
"rustc" "+nightly-2020-08-26" "--target" "thumbv8m.main-none-eabihf" "--cfg=armv7m" "--cfg=armv8m" "--cfg=armv8m_main" "--cfg=has_fpu" "-g" "-O" "-Clto=yes" "-Cforce-frame-pointers=no" "--remap-path-prefix" "/Users/ovidiu/Projects/cortex-m=." "--emit=obj" "-o" "bin/thumbv8m.main-none-eabihf.o" "asm/lib.rs"
"rustc" "+nightly-2020-08-26" "--target" "thumbv8m.main-none-eabihf" "--cfg=armv7m" "--cfg=armv8m" "--cfg=armv8m_main" "--cfg=has_fpu" "-g" "-O" "-Clto=yes" "-Cforce-frame-pointers=no" "--remap-path-prefix" "/Users/ovidiu/Projects/cortex-m=." "--emit=obj" "-Clinker-plugin-lto" "-o" "bin/thumbv8m.main-none-eabihf-lto.o" "asm/lib.rs"
~/Projects/cortex-m fix-delay-underflow ❯ git status
On branch fix-delay-underflow
Your branch is up to date with 'origin/fix-delay-underflow'.

nothing to commit, working tree clean
~/Projects/cortex-m fix-delay-underflow ❯ git push
Everything up-to-date
~/Projects/cortex-m fix-delay-underflow ❯

[jonas-schievink]

bors r+

[bors]

Build succeeded:

• ci-linux (1.38.0)
• ci-linux (stable)
• clippy
• rustfmt

[David-OConnor]

I can confirm this. Just started getting it on the f3 hal's adc setup.

[adamgreig]

I can confirm this. Just started getting it on the f3 hal's adc setup.

This should have been fixed in cortex-m 0.7.1 which was released a while back, what version of cortex-m are you using?

[David-OConnor]

I tried versions 0.6.5, 0.7.0, and 0.7.1. The most recent version I had been using where it worked was 0.6.4.

This function in adc.rs in stm32f3xx hal was crashing it:

fn wait_advregen_startup(&self) {
    asm::delay(MAX_ADVREGEN_STARTUP_US * 1_000_000) / self.clocks.sysclk().0);
}

I patched it to be this, which stopped the crashes:

fn wait_advregen_startup(&self) {
    let mut delay = (MAX_ADVREGEN_STARTUP_US * 1_000_000) / self.clocks.sysclk().0;
    if delay < 2 {
        delay = 2;
    }
    asm::delay(delay);
}

MAX_ADV... is 10, and the clocks are often 72e6, so this works out to less than 2. I tried manually delaying for 0, 1, and 2. 0 and 1 crash, 2 doesn't.

[ovidiusabou]

0.7.1 doesn't include the fix from this PR from what I can see.

[adamgreig]

Oops, you're quite right, I was thinking of #317 instead. Are you able to test with cortex-m master from this repository?