cpu: msp430-common: fix context save/restore

Previously, __restore_context was meddling with the to-be-restored
context SR on the stack, not correctly restoring GIE.
Now, we let the CPU restore the correct status register as saved in
__save_context.

Contains some simplification of the context save/restore logic.

cpu/msp430-common/cpu.c

@@ -21,18 +21,15 @@
  */
 __attribute__((naked)) void thread_yield_higher(void)
 {
-    /*
+    __asm__("push r2"); /* save SR */
-     * disable IRQ, remembering if they are
+    __disable_irq();
-     * to be reactivated after context switch
-     */
-    unsigned int irqen = disableIRQ();
 
     __save_context();
 
     /* have sched_active_thread point to the next thread */
     sched_run();
 
-    __restore_context(irqen);
+    __restore_context();
 
     UNREACHABLE();
 }
@@ -42,7 +39,7 @@ NORETURN void cpu_switch_context_exit(void)
     sched_active_thread = sched_threads[0];
     sched_run();
 
-    __restore_context(GIE);
+    __restore_context();
 
     UNREACHABLE();
 }

cpu/msp430-common/include/cpu.h

@@ -52,6 +52,28 @@ extern "C" {
 #define dINT            disableIRQ
 /** @} */
 
+/**
+ * @brief Globally disable IRQs
+ */
+static inline void __attribute__((always_inline)) __disable_irq(void)
+{
+    __asm__ __volatile__("bic  %0, r2" : : "i"(GIE));
+    /* this NOP is needed to handle a "delay slot" that all MSP430 MCUs
+       impose silently after messing with the GIE bit, DO NOT REMOVE IT! */
+    __asm__ __volatile__("nop");
+}
+
+/**
+ * @brief Globally enable IRQs
+ */
+static inline void __attribute__((always_inline)) __enable_irq(void)
+{
+    __asm__ __volatile__("bis  %0, r2" : : "i"(GIE));
+    /* this NOP is needed to handle a "delay slot" that all MSP430 MCUs
+       impose silently after messing with the GIE bit, DO NOT REMOVE IT! */
+    __asm__ __volatile__("nop");
+}
+
 /**
  * @brief   The current ISR state (inside or not)
  */
@@ -65,7 +87,7 @@ extern char __isr_stack[MSP430_ISR_STACK_SIZE];
 /**
  * @brief   Save the current thread context from inside an ISR
  */
-inline void __save_context_isr(void)
+static inline void __attribute__((always_inline)) __save_context(void)
 {
     __asm__("push r15");
     __asm__("push r14");
@@ -86,7 +108,7 @@ inline void __save_context_isr(void)
 /**
  * @brief   Restore the thread context from inside an ISR
  */
-inline void __restore_context_isr(void)
+static inline void __attribute__((always_inline)) __restore_context(void)
 {
     __asm__("mov.w %0,r1" : : "m"(sched_active_thread->sp));
 
@@ -102,14 +124,15 @@ inline void __restore_context_isr(void)
     __asm__("pop r13");
     __asm__("pop r14");
     __asm__("pop r15");
+    __asm__("reti");
 }
 
 /**
  * @brief   Run this code on entering interrupt routines
  */
-inline void __enter_isr(void)
+static inline void __attribute__((always_inline)) __enter_isr(void)
 {
-    __save_context_isr();
+    __save_context();
     __asm__("mov.w %0,r1" : : "i"(__isr_stack + MSP430_ISR_STACK_SIZE));
     __inISR = 1;
 }
@@ -117,7 +140,7 @@ inline void __enter_isr(void)
 /**
  * @brief   Run this code on exiting interrupt routines
  */
-inline void __exit_isr(void)
+static inline void __attribute__((always_inline)) __exit_isr(void)
 {
     __inISR = 0;
 
@@ -125,41 +148,7 @@ inline void __exit_isr(void)
         sched_run();
     }
 
-    __restore_context_isr();
+    __restore_context();
-    __asm__("reti");
-}
-
-/**
- * @brief   Save the current context on the stack
- */
-inline void __save_context(void)
-{
-    __asm__("push r2"); /* save SR */
-    __save_context_isr();
-}
-
-/**
- * @brief   Restore the thread context from the stack
- *
- * @param[in] irqen     former interrupt state
- */
-inline void __restore_context(unsigned int irqen)
-{
-    __restore_context_isr();
-
-    /*
-     * we want to enable appropriate IRQs *just after*
-     * quitting the interrupt handler; to that end,
-     * we change the GIE bit in the value to be restored
-     * in R2 (a.k.a. SR) by the next RETI instruction
-     */
-    if (irqen) {
-        __asm__("bis.w #8, 0(r1)");
-    } else {
-        __asm__("bic.w #8, 0(r1)");
-    }
-
-    __asm__("reti");
 }
 
 /**

cpu/msp430-common/irq.c

@@ -33,11 +33,7 @@ unsigned int disableIRQ(void)
     state &= GIE;
 
     if (state) {
-        /*    puts("-"); */
+        __disable_irq();
-        __asm__ __volatile__("bic  %0, r2" : : "i"(GIE));
-       /* this NOP is needed to handle a "delay slot" that all MSP430 MCUs
-          impose silently after messing with the GIE bit, DO NOT REMOVE IT! */
-        __asm__ __volatile__("nop");
     }
 
     return state;
@@ -50,10 +46,7 @@ unsigned int enableIRQ(void)
     state &= GIE;
 
     if (!state) {
-        __asm__ __volatile__("bis  %0, r2" : : "i"(GIE));
+        __enable_irq();
-        /* this NOP is needed to handle a "delay slot" that all MSP430 MCUs
-           impose silently after messing with the GIE bit, DO NOT REMOVE IT! */
-        __asm__ __volatile__("nop");
     }
 
     return state;
@@ -62,10 +55,7 @@ unsigned int enableIRQ(void)
 void restoreIRQ(unsigned int state)
 {
     if (state) {
-        __asm__ __volatile__("bis  %0, r2" : : "i"(GIE));
+        __enable_irq();
-        /* this NOP is needed to handle a "delay slot" that all MSP430 MCUs
-           impose silently after messing with the GIE bit, DO NOT REMOVE IT! */
-        __asm__ __volatile__("nop");
     }
 }