arch/arm/src/armv7-m: Add support of nested interrupts

This patch adds the support of nested interrupts for armv7-m
architecture.

Signed-off-by: Drashti Parikh <[email protected]>

os/arch/Kconfig

@@ -13,6 +13,7 @@ config ARCH_ARM
 	select ARCH_HAVE_VFORK
 	select ARCH_HAVE_STACKCHECK
 	select ARCH_HAVE_CUSTOMOPT
+	select ARCH_HAVE_NESTED_INTERRUPT
 	---help---
 		The ARM architectures
 
@@ -571,6 +572,20 @@ config ARCH_INTERRUPTSTACK
 		defined to be zero), the user task stacks will be used during interrupt
 		handling.
 
+config ARCH_HAVE_NESTED_INTERRUPT
+	bool
+	default n
+
+if ARCH_INTERRUPTSTACK > 7
+config ARCH_NESTED_INTERRUPT
+	bool "Nested interrupt support"
+	depends on ARCH_HAVE_NESTED_INTERRUPT
+	default n
+	---help---
+		Enables the nested interrupt support. If defined, higher priority interrupt
+		can pre-empt the lower priority interrupt.
+endif
+
 config ARCH_HAVE_HIPRI_INTERRUPT
 	bool
 	default n

os/arch/arm/src/armv7-m/up_doirq.c

@@ -73,7 +73,9 @@
 /****************************************************************************
  * Public Data
  ****************************************************************************/
-
+#if CONFIG_ARCH_INTERRUPTSTACK > 7
+extern uint32_t g_nestlevel; /* Initial top of interrupt stack */
+#endif
 /****************************************************************************
  * Private Data
  ****************************************************************************/
@@ -88,10 +90,31 @@
 
 uint32_t *up_doirq(int irq, uint32_t *regs)
 {
+#if CONFIG_ARCH_INTERRUPTSTACK > 7
+	irqstate_t flags;
+#endif
 	board_led_on(LED_INIRQ);
 #ifdef CONFIG_SUPPRESS_INTERRUPTS
 	PANIC();
 #else
+
+#if CONFIG_ARCH_INTERRUPTSTACK > 7
+	/* Current regs non-zero indicates that we are processing an interrupt;
+	 * regs holds the state of the interrupted logic; current_regs holds the
+	 * state of the interrupted user task.  current_regs should, therefor,
+	 * only be modified for outermost interrupt handler (when g_nestlevel == 0)
+	 */
+
+	flags = irqsave();
+
+	if (g_nestlevel == 0) {
+		current_regs = regs;
+	}
+
+	g_nestlevel++;
+
+	irqrestore(flags);
+#else
 	uint32_t *savestate;
 
 	/* Nested interrupts are not supported in this implementation.  If you want
@@ -101,22 +124,41 @@ uint32_t *up_doirq(int irq, uint32_t *regs)
 	 * that purpose as implemented here because only the outermost nested
 	 * interrupt can result in a context switch (it can probably be deleted).
 	 */
-
-	/* Current regs non-zero indicates that we are processing an interrupt;
-	 * current_regs is also used to manage interrupt level context switches.
-	 */
-
 	savestate = (uint32_t *)current_regs;
 	current_regs = regs;
-
 	/* Acknowledge the interrupt */
 
 	up_ack_irq(irq);
+#endif
 
 	/* Deliver the IRQ */
 
 	irq_dispatch(irq, regs);
 
+#if CONFIG_ARCH_INTERRUPTSTACK > 7
+	/* Context switches are indicated by the returned value of this function.
+	 * If a context switch occurred while processing the interrupt then
+	 * current_regs may have change value.  If we return any value different
+	 * from the input regs, then the lower level will know that a context
+	 * switch occurred during interrupt processing.  Context switching should
+	 * only be performed when the outermost interrupt handler returns.
+	 */
+
+	flags = irqsave();
+
+	g_nestlevel--;
+
+	if (g_nestlevel == 0) {
+		regs = (uint32_t*)current_regs;
+		current_regs = NULL;
+	}
+
+	/* Note that interrupts are left disabled.  This needed if context switch
+	 * will be performed.  But, any case, the correct interrupt state should
+	 * be restored when returning from the interrupt.
+	 */
+
+#else
 	/* If a context switch occurred while processing the interrupt then
 	 * current_regs may have change value.  If we return any value different
 	 * from the input regs, then the lower level will know that a context
@@ -131,6 +173,7 @@ uint32_t *up_doirq(int irq, uint32_t *regs)
 	 */
 
 	current_regs = savestate;
+#endif
 #endif
 	board_led_off(LED_INIRQ);
 	return regs;

os/arch/arm/src/armv7-m/up_lazyexception.S

@@ -205,14 +205,15 @@ exception_common:
 	stmdb	sp!, {r2-r11}			/* Save the remaining registers plus the SP value */
 #endif
 
-#ifndef CONFIG_ARCH_HIPRI_INTERRUPT
+#if !defined(CONFIG_ARCH_HIPRI_INTERRUPT) && !defined(CONFIG_ARCH_NESTED_INTERRUPT)
+
 	/* Disable interrupts, select the stack to use for interrupt handling
 	 * and call up_doirq to handle the interrupt
 	 */
 
 	cpsid	i						/* Disable further interrupts */
 
-#else
+#elif !defined(CONFIG_ARCH_NESTED_INTERRUPT)
 	/* Set the BASEPRI register so that further normal interrupts will be
 	 * masked.  Nested, high priority may still occur, however.
 	 *
@@ -240,13 +241,17 @@ exception_common:
 	mov		r4, sp
 
 #if CONFIG_ARCH_INTERRUPTSTACK > 7
-	/* If CONFIG_ARCH_INTERRUPTSTACK is defined, we will set the MSP to use
-	 * a special special interrupt stack pointer.  The way that this is done
-	 * here prohibits nested interrupts without some additional logic!
-	 */
 
-	setintstack	r2, r3
+	/* If g_nestlevel is zero then behave as normal, switching from the user
+	 * to the interrupt stack; if g_nestlevel is greater than zero, then do
+	 * not switch stacks. In this latter case, we are already using the interrupt stack */
 
+	ldr		r5, =g_nestlevel
+	ldr		r6, [r5]
+	cmp		r6, #0
+	bne		9f
+	ldr		sp, =g_intstackbase
+9:
 #else
 	/* Otherwise, we will re-use the interrupted thread's stack.  That may
 	 * mean using either MSP or PSP stack for interrupt level processing (in
@@ -370,7 +375,7 @@ exception_common:
 
 #ifdef CONFIG_ARMV7M_USEBASEPRI
 	msr		basepri, r3				/* Restore interrupts priority masking */
-#ifndef CONFIG_ARCH_HIPRI_INTERRUPT
+#if !defined(CONFIG_ARCH_HIPRI_INTERRUPT) && !defined(CONFIG_ARCH_NESTED_INTERRUPT)
 	cpsie	i						/* Re-enable interrupts */
 #endif
 
@@ -397,11 +402,16 @@ exception_common:
 	.bss
 	.global	g_intstackalloc
 	.global	g_intstackbase
+	.global	g_nestlevel
 	.align	8
 g_intstackalloc:
 	.skip	((CONFIG_ARCH_INTERRUPTSTACK + 4) & ~7)
 g_intstackbase:
 	.size	g_intstackalloc, .-g_intstackalloc
+	.skip 	4
+g_nestlevel:
+	.skip   4
+	.size   g_nestlevel, 4
 #endif
 
 	.end