riot-rs-threads: cortex-m: make sched() deal with no previous thread

future-proof-iot · Apr 17, 2024 · 7d30fbe · 7d30fbe
1 parent 2084409
commit 7d30fbe
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Showing 3 changed files with 10 additions and 78 deletions.
diff --git a/src/riot-rs-threads/src/arch/cortex_m.rs b/src/riot-rs-threads/src/arch/cortex_m.rs
@@ -62,65 +62,11 @@ impl Arch for Cpu {
     }
 
     #[inline(always)]
-    fn start_threading(next_sp: usize) {
-        cortex_m::interrupt::disable();
+    fn start_threading() {
         Self::schedule();
-        unsafe {
-            asm!(
-                "
-                msr psp, r1 // set new thread's SP to PSP
-                cpsie i     // enable interrupts, otherwise svc hard faults
-                svc 0       // SVC 0 handles switching
-                ",
-            in("r1")next_sp);
-        }
     }
 }
 
-#[cfg(any(armv7m, armv8m))]
-#[naked]
-#[no_mangle]
-#[allow(non_snake_case)]
-unsafe extern "C" fn SVCall() {
-    unsafe {
-        asm!(
-            "
-            movw LR, #0xFFFd
-            movt LR, #0xFFFF
-            bx lr
-            ",
-            options(noreturn)
-        )
-    };
-}
-
-#[cfg(armv6m)]
-#[naked]
-#[no_mangle]
-#[allow(non_snake_case)]
-unsafe extern "C" fn SVCall() {
-    unsafe {
-        asm!(
-            "
-            /* label rules:
-             * - number only
-             * - no combination of *only* [01]
-             * - add f or b for 'next matching forward/backward'
-             * so let's use '99' forward ('99f')
-             */
-            ldr r0, 99f
-            mov LR, r0
-            bx lr
-
-            .align 4
-            99:
-            .word 0xFFFFFFFD
-            ",
-            options(noreturn)
-        )
-    };
-}
-
 #[cfg(any(armv7m, armv8m))]
 #[naked]
 #[no_mangle]
@@ -129,7 +75,6 @@ unsafe extern "C" fn PendSV() {
     unsafe {
         asm!(
             "
-            mrs r0, psp
             cpsid i
             bl {sched}
             cpsie i
@@ -163,7 +108,6 @@ unsafe extern "C" fn PendSV() {
     unsafe {
         asm!(
             "
-            mrs r0, psp
             cpsid i
             bl sched
             cpsie i
@@ -214,9 +158,6 @@ unsafe extern "C" fn PendSV() {
 /// It selects the next thread that should run from the runqueue.
 /// This may be current thread, or a new one.
 ///
-/// Input:
-/// - old_sp (`r0`): the stack pointer of the currently running thread.
-///
 /// Returns:
 /// - `0` in `r0` if the next thread in the runqueue is the currently running thread
 /// - Else it writes into the following registers:
@@ -227,7 +168,7 @@ unsafe extern "C" fn PendSV() {
 /// This function is called in PendSV.
 // TODO: make arch independent, or move to arch
 #[no_mangle]
-unsafe fn sched(old_sp: usize) -> usize {
+unsafe fn sched() -> usize {
     // SAFETY: interrupts are disabled by caller
     let cs = unsafe { CriticalSection::new() };
     let next_pid;
@@ -255,7 +196,7 @@ unsafe fn sched(old_sp: usize) -> usize {
             return 0;
         }
         //println!("current: {} next: {}", current_pid, next_pid);
-        threads.threads[current_pid as usize].sp = old_sp;
+        threads.threads[current_pid as usize].sp = cortex_m::register::psp::read() as usize;
         threads.current_thread = Some(next_pid);
         current_high_regs = threads.threads[current_pid as usize].data.as_ptr();
     } else {

diff --git a/src/riot-rs-threads/src/arch/mod.rs b/src/riot-rs-threads/src/arch/mod.rs
@@ -19,7 +19,7 @@ pub trait Arch {
     fn schedule();
 
     /// Setup and initiate the first context switch.
-    fn start_threading(next_sp: usize);
+    fn start_threading();
 }
 
 cfg_if::cfg_if! {
@@ -36,7 +36,7 @@ cfg_if::cfg_if! {
             fn setup_stack(_: &mut [u8], _: usize, _: usize) -> usize {
                 unimplemented!()
             }
-            fn start_threading(_: usize) {
+            fn start_threading() {
                 unimplemented!()
             }
             fn schedule() {

diff --git a/src/riot-rs-threads/src/lib.rs b/src/riot-rs-threads/src/lib.rs
@@ -6,8 +6,6 @@
 // invariants
 #![allow(clippy::indexing_slicing)]
 
-use critical_section::CriticalSection;
-
 use riot_rs_runqueue::RunQueue;
 pub use riot_rs_runqueue::{RunqueueId, ThreadId};
 
@@ -176,20 +174,13 @@ impl Threads {
 ///
 /// # Safety
 ///
-/// This may only be called once.
-///
-/// # Panics
+/// This function is crafted to be called at a specific point in the RIOT-rs
+/// initialization, by `riot-rs-rt`. Don't call this unless you know you need to.
 ///
-/// Panics if no thread exists.
+/// Currently it expects at least:
+/// - Cortex-M: to be called from the reset handler while MSP is active
 pub unsafe fn start_threading() {
-    // faking a critical section to get THREADS
-    // SAFETY: caller ensures invariants
-    let cs = unsafe { CriticalSection::new() };
-    let next_sp = THREADS.with_mut_cs(cs, |mut threads| {
-        let next_pid = threads.runqueue.get_next().unwrap();
-        threads.threads[next_pid as usize].sp
-    });
-    Cpu::start_threading(next_sp);
+    Cpu::start_threading();
 }
 
 /// Trait for types that fit into a single register.