Backported improvement to the CM0 port from version 2.3.0.

git-svn-id: svn://svn.code.sf.net/p/chibios/svn/branches/stable_2.2.x@2823 35acf78f-673a-0410-8e92-d51de3d6d3f4

docs/Doxyfile

@@ -31,7 +31,7 @@ PROJECT_NAME           = ChibiOS/RT
 # This could be handy for archiving the generated documentation or 
 # if some version control system is used.
 
-PROJECT_NUMBER         = 2.2.2
+PROJECT_NUMBER         = 2.2.3
 
 # The OUTPUT_DIRECTORY tag is used to specify the (relative or absolute) 
 # base path where the generated documentation will be put. 

os/kernel/include/ch.h

@@ -46,7 +46,7 @@
 /**
  * @brief   Kernel version string.
  */
-#define CH_KERNEL_VERSION       "2.2.2"
+#define CH_KERNEL_VERSION       "2.2.3"
 
 /**
  * @brief   Kernel version major number.
@@ -61,7 +61,7 @@
 /**
  * @brief   Kernel version patch number.
  */
-#define CH_KERNEL_PATCH         2
+#define CH_KERNEL_PATCH         3
 
 /*
  * Common values.

os/ports/GCC/ARMCMx/chcore_v6m.c

@@ -34,11 +34,6 @@
 
 #include "ch.h"
 
-/**
- * @brief   PC register temporary storage.
- */
-regarm_t _port_saved_pc;
-
 /**
  * @brief   System Timer vector.
  * @details This interrupt is used as system tick.
@@ -55,40 +50,39 @@ CH_IRQ_HANDLER(SysTickVector) {
   CH_IRQ_EPILOGUE();
 }
 
+/**
+ * @brief   NMI vector.
+ * @details The NMI vector is used for exception mode re-entering after a
+ *          context switch.
+ */
+void NMIVector(void) {
+  register struct extctx *ctxp;
+
+  /* Discarding the current exception context and positioning the stack to
+     point to the real one.*/
+  asm volatile ("mrs     %0, PSP" : "=r" (ctxp) : : "memory");
+  ctxp++;
+  asm volatile ("msr     PSP, %0" : : "r" (ctxp) : "memory");
+  port_unlock_from_isr();
+}
+
 /**
  * @brief   Post-IRQ switch code.
- * @details On entry the stack and the registers are restored by the exception
+ * @details The switch is performed in thread context then an NMI exception
- *          return, the PC value is stored in @p _port_saved_pc, the interrupts
+ *          is enforced in order to return to the exact point before the
- *          are disabled.
+ *          preemption.
  */
 #if !defined(__DOXYGEN__)
 __attribute__((naked))
 #endif
 void _port_switch_from_isr(void) {
-  /* Note, saves r4 to make space for the PC.*/
-  asm volatile ("push    {r0, r1, r2, r3, r4}                   \n\t"
-                "mrs     r0, APSR                               \n\t"
-                "mov     r1, r12                                \n\t"
-                "push    {r0, r1, lr}                           \n\t"
-                "ldr     r0, =_port_saved_pc                    \n\t"
-                "ldr     r0, [r0]                               \n\t"
-                "add     r0, r0, #1                             \n\t"
-                "str     r0, [sp, #28]" : : : "memory");
 
   chSchDoRescheduleI();
-
+  SCB_ICSR = ICSR_NMIPENDSET;
-  /* Note, the last register is restored alone after re-enabling the
+  /* The following loop should never be executed, the NMI will kick in
-     interrupts in order to minimize the (very remote and unlikely)
+     immediately.*/
-     possibility that the stack is filled by continuous and saturating
+  while (TRUE)
-     interrupts that would not allow that last words to be pulled out of
+    ;
-     the stack.*/
-  asm volatile ("pop     {r0, r1, r2}                           \n\t"
-                "mov     r12, r1                                \n\t"
-                "msr     APSR, r0                               \n\t"
-                "mov     lr, r2                                 \n\t"
-                "pop     {r0, r1, r2, r3}                       \n\t"
-                "cpsie   i                                      \n\t"
-                "pop     {pc}" : : : "memory");
 }
 
 #define PUSH_CONTEXT(sp) {                                                  \
@@ -140,6 +134,33 @@ void port_switch(Thread *ntp, Thread *otp) {
   POP_CONTEXT(r13);
 }
 
+/**
+ * @brief   IRQ epilogue code.
+ *
+ * @param[in] lr        value of the @p LR register on ISR entry
+ */
+void _port_irq_epilogue(regarm_t lr) {
+
+  if (lr != (regarm_t)0xFFFFFFF1) {
+    port_lock_from_isr();
+    if (chSchIsRescRequiredExI()) {
+      register struct extctx *ctxp;
+
+      /* Adding an artificial exception return context, there is no need to
+         populate it fully.*/
+      asm volatile ("mrs     %0, PSP" : "=r" (ctxp) : : "memory");
+      ctxp--;
+      asm volatile ("msr     PSP, %0" : : "r" (ctxp) : "memory");
+      ctxp->pc = _port_switch_from_isr;
+      ctxp->xpsr = (regarm_t)0x01000000;
+      /* Note, returning without unlocking is intentional, this is done in
+        order to keep the rest of the context switching atomic.*/
+      return;
+    }
+    port_unlock_from_isr();
+  }
+}
+
 /**
  * @brief   Start a thread by invoking its work function.
  * @details If the work function returns @p chThdExit() is automatically

os/ports/GCC/ARMCMx/chcore_v6m.h

@@ -39,10 +39,8 @@
 /* Port implementation part.                                                 */
 /*===========================================================================*/
 
-/**
+#if !defined(__DOXYGEN__)
- * @brief   Cortex-Mx exception context.
+struct extctx {
- */
-struct cmxctx {
   regarm_t      r0;
   regarm_t      r1;
   regarm_t      r2;
@@ -53,18 +51,6 @@ struct cmxctx {
   regarm_t      xpsr;
 };
 
-#if !defined(__DOXYGEN__)
-struct extctx {
-  regarm_t      xpsr;
-  regarm_t      r12;
-  regarm_t      lr;
-  regarm_t      r0;
-  regarm_t      r1;
-  regarm_t      r2;
-  regarm_t      r3;
-  regarm_t      pc;
-};
-
 struct intctx {
   regarm_t      r8;
   regarm_t      r9;
@@ -134,20 +120,7 @@ struct intctx {
  * @details This macro must be inserted at the end of all IRQ handlers
  *          enabled to invoke system APIs.
  */
-#define PORT_IRQ_EPILOGUE() {                                               \
+#define PORT_IRQ_EPILOGUE() _port_irq_epilogue(_saved_lr)
-  if (_saved_lr != (regarm_t)0xFFFFFFF1) {                                  \
-    port_lock_from_isr();                                                   \
-    if (chSchIsRescRequiredExI()) {                                         \
-      register struct cmxctx *ctxp;                                         \
-                                                                            \
-      asm volatile ("mrs     %0, PSP" : "=r" (ctxp) : );                    \
-      _port_saved_pc = ctxp->pc;                                            \
-      ctxp->pc = _port_switch_from_isr;                                     \
-      return;                                                               \
-    }                                                                       \
-    port_unlock_from_isr();                                                 \
-  }                                                                         \
-}
 
 /**
  * @brief   IRQ handler function declaration.
@@ -233,15 +206,12 @@ struct intctx {
 #define port_wait_for_interrupt()
 #endif
 
-#if !defined(__DOXYGEN__)
-extern regarm_t _port_saved_pc;
-#endif
-
 #ifdef __cplusplus
 extern "C" {
 #endif
   void port_halt(void);
   void port_switch(Thread *ntp, Thread *otp);
+  void _port_irq_epilogue(regarm_t lr);
   void _port_switch_from_isr(void);
   void _port_thread_start(void);
 #ifdef __cplusplus

readme.txt

@@ -68,6 +68,13 @@
 *** Releases                                                              ***
 *****************************************************************************
 
+*** 2.2.3 ***
+- NEW: Improved preemption implementation for the Cortex-M0, now it uses
+  the NMI vector in order to restore the original context. The change makes
+  IRQ handling faster and also saves some RAM/ROM space. The GCC port code
+  now does not inline the epilogue code in each ISR saving significant ROM
+  space for each interrupt handler in the system.
+
 *** 2.2.2 ***
 - FIX: Fixed race condition in CM0 ports, the fix also improves the
   ISR latency (bug 3193062).