Add support for the configUSE_TASK_FPU_SUPPORT constant in the GCC/ARM_CR5 port (#584)

* Add support for the configUSE_TASK_FPU_SUPPORT in the GCC/ARM_CR5 port

This is done almost identically as in the GCC/ARM_CA9 port

* Adjust task stack initialitation of the GCC/ARM_CR5 port

Ensure that the task stack initialization is done correctly for the
different options of configUSE_TASK_FPU_SUPPORT.

This is very similar to the GCC/ARM_CA9 port. The only meaningful
difference is, that the FPU of the Cortex-R5 has just sixteen 64-bit
floating point registers as it implements the VFPv3-D16 architecture.
You may also refer to the ARM documentation

* Add support for FPU safe interrupts to the GCC/ARM_CR5 port

Similar to GCC/ARM_CA9 port

* Clarify comment about the size of the FPU registers of Cortex R5

portable/GCC/ARM_CR5/port.c

@@ -28,6 +28,7 @@
 
 /* Standard includes. */
 #include <stdlib.h>
+#include <string.h>
 
 /* Scheduler includes. */
 #include "FreeRTOS.h"
@@ -148,6 +149,19 @@
     #define portTASK_RETURN_ADDRESS    prvTaskExitError
 #endif
 
+/*
+ * The space on the stack required to hold the FPU registers.
+ *
+ * The ARM Cortex R5 processor implements the VFPv3-D16 FPU
+ * architecture. This includes only 16 double-precision registers,
+ * instead of 32 as is in VFPv3. The register bank can be viewed
+ * either as sixteen 64-bit double-word registers (D0-D15) or
+ * thirty-two 32-bit single-word registers (S0-S31), in both cases
+ * the size of the bank remains the same. The FPU has also a 32-bit
+ * status register.
+ */
+#define portFPU_REGISTER_WORDS    ( ( 16 * 2 ) + 1 )
+
 /*-----------------------------------------------------------*/
 
 /*
@@ -161,6 +175,27 @@ extern void vPortRestoreTaskContext( void );
  */
 static void prvTaskExitError( void );
 
+/*
+ * If the application provides an implementation of vApplicationIRQHandler(),
+ * then it will get called directly without saving the FPU registers on
+ * interrupt entry, and this weak implementation of
+ * vApplicationFPUSafeIRQHandler() is just provided to remove linkage errors -
+ * it should never actually get called so its implementation contains a
+ * call to configASSERT() that will always fail.
+ *
+ * If the application provides its own implementation of
+ * vApplicationFPUSafeIRQHandler() then the implementation of
+ * vApplicationIRQHandler() provided in portASM.S will save the FPU registers
+ * before calling it.
+ *
+ * Therefore, if the application writer wants FPU registers to be saved on
+ * interrupt entry their IRQ handler must be called
+ * vApplicationFPUSafeIRQHandler(), and if the application writer does not want
+ * FPU registers to be saved on interrupt entry their IRQ handler must be
+ * called vApplicationIRQHandler().
+ */
+void vApplicationFPUSafeIRQHandler( uint32_t ulICCIAR ) __attribute__((weak) );
+
 /*-----------------------------------------------------------*/
 
 /* A variable is used to keep track of the critical section nesting.  This
@@ -255,12 +290,31 @@ StackType_t * pxPortInitialiseStack( StackType_t * pxTopOfStack,
     /* The task will start with a critical nesting count of 0 as interrupts are
      * enabled. */
     *pxTopOfStack = portNO_CRITICAL_NESTING;
-    pxTopOfStack--;
 
-    /* The task will start without a floating point context.  A task that uses
-     * the floating point hardware must call vPortTaskUsesFPU() before executing
-     * any floating point instructions. */
+    #if( configUSE_TASK_FPU_SUPPORT == 1 )
+    {
+        /* The task will start without a floating point context.  A task that
+        uses the floating point hardware must call vPortTaskUsesFPU() before
+        executing any floating point instructions. */
+        pxTopOfStack--;
         *pxTopOfStack = portNO_FLOATING_POINT_CONTEXT;
+    }
+    #elif( configUSE_TASK_FPU_SUPPORT == 2 )
+    {
+        /* The task will start with a floating point context.  Leave enough
+        space for the registers - and ensure they are initialized to 0. */
+        pxTopOfStack -= portFPU_REGISTER_WORDS;
+        memset( pxTopOfStack, 0x00, portFPU_REGISTER_WORDS * sizeof( StackType_t ) );
+
+        pxTopOfStack--;
+        *pxTopOfStack = pdTRUE;
+        ulPortTaskHasFPUContext = pdTRUE;
+    }
+    #else
+    {
+        #error Invalid configUSE_TASK_FPU_SUPPORT setting - configUSE_TASK_FPU_SUPPORT must be set to 1, 2, or left undefined.
+    }
+    #endif /* configUSE_TASK_FPU_SUPPORT */
 
     return pxTopOfStack;
 }
@@ -283,6 +337,13 @@ static void prvTaskExitError( void )
 }
 /*-----------------------------------------------------------*/
 
+void vApplicationFPUSafeIRQHandler( uint32_t ulICCIAR )
+{
+    ( void ) ulICCIAR;
+    configASSERT( ( volatile void * ) NULL );
+}
+/*-----------------------------------------------------------*/
+
 BaseType_t xPortStartScheduler( void )
 {
     uint32_t ulAPSR, ulCycles = 8; /* 8 bits per byte. */
@@ -444,8 +505,10 @@ void FreeRTOS_Tick_Handler( void )
 }
 /*-----------------------------------------------------------*/
 
-void vPortTaskUsesFPU( void )
-{
+#if( configUSE_TASK_FPU_SUPPORT != 2 )
+
+    void vPortTaskUsesFPU( void )
+    {
         uint32_t ulInitialFPSCR = 0;
 
         /* A task is registering the fact that it needs an FPU context.  Set the
@@ -454,7 +517,9 @@ void vPortTaskUsesFPU( void )
 
         /* Initialise the floating point status register. */
         __asm volatile ( "FMXR 	FPSCR, %0" ::"r" ( ulInitialFPSCR ) : "memory" );
-}
+    }
+
+#endif /* configUSE_TASK_FPU_SUPPORT */
 /*-----------------------------------------------------------*/
 
 void vPortClearInterruptMask( uint32_t ulNewMaskValue )

portable/GCC/ARM_CR5/portASM.S

@@ -262,6 +262,42 @@ switch_before_exit:
 	next. */
 	portRESTORE_CONTEXT
 
+/******************************************************************************
+ * If the application provides an implementation of vApplicationIRQHandler(),
+ * then it will get called directly without saving the FPU registers on
+ * interrupt entry, and this weak implementation of
+ * vApplicationIRQHandler() will not get called.
+ *
+ * If the application provides its own implementation of
+ * vApplicationFPUSafeIRQHandler() then this implementation of
+ * vApplicationIRQHandler() will be called, save the FPU registers, and then
+ * call vApplicationFPUSafeIRQHandler().
+ *
+ * Therefore, if the application writer wants FPU registers to be saved on
+ * interrupt entry their IRQ handler must be called
+ * vApplicationFPUSafeIRQHandler(), and if the application writer does not want
+ * FPU registers to be saved on interrupt entry their IRQ handler must be
+ * called vApplicationIRQHandler().
+ *****************************************************************************/
+
+.align 4
+.weak vApplicationIRQHandler
+.type vApplicationIRQHandler, %function
+vApplicationIRQHandler:
+	PUSH	{LR}
+	FMRX	R1,  FPSCR
+	VPUSH	{D0-D15}
+	PUSH	{R1}
+
+	LDR		r1, vApplicationFPUSafeIRQHandlerConst
+	BLX		r1
+
+	POP		{R0}
+	VPOP	{D0-D15}
+	VMSR	FPSCR, R0
+
+	POP {PC}
+
 ulICCIARConst:	.word ulICCIAR
 ulICCEOIRConst:	.word ulICCEOIR
 ulICCPMRConst: .word ulICCPMR
@@ -272,6 +308,7 @@ ulMaxAPIPriorityMaskConst: .word ulMaxAPIPriorityMask
 vTaskSwitchContextConst: .word vTaskSwitchContext
 vApplicationIRQHandlerConst: .word vApplicationIRQHandler
 ulPortInterruptNestingConst: .word ulPortInterruptNesting
+vApplicationFPUSafeIRQHandlerConst: .word vApplicationFPUSafeIRQHandler
 
 .end
 

portable/GCC/ARM_CR5/portmacro.h

@@ -116,9 +116,18 @@
  * handler for whichever peripheral is used to generate the RTOS tick. */
     void FreeRTOS_Tick_Handler( void );
 
-/* Any task that uses the floating point unit MUST call vPortTaskUsesFPU()
- * before any floating point instructions are executed. */
+/* If configUSE_TASK_FPU_SUPPORT is set to 1 (or left undefined) then tasks are
+created without an FPU context and must call vPortTaskUsesFPU() to give
+themselves an FPU context before using any FPU instructions. If
+configUSE_TASK_FPU_SUPPORT is set to 2 then all tasks will have an FPU context
+by default. */
+#if( configUSE_TASK_FPU_SUPPORT != 2 )
     void vPortTaskUsesFPU( void );
+#else
+    /* Each task has an FPU context already, so define this function away to
+    nothing to prevent it being called accidentally. */
+    #define vPortTaskUsesFPU()
+#endif /* configUSE_TASK_FPU_SUPPORT */
     #define portTASK_USES_FLOATING_POINT()    vPortTaskUsesFPU()
 
     #define portLOWEST_INTERRUPT_PRIORITY           ( ( ( uint32_t ) configUNIQUE_INTERRUPT_PRIORITIES ) - 1UL )