SAMV7/Cortex-M7: Add support for write through D-Cache. SAMV7 Ethernet look like it needs this

arch/arm/src/armv7-m/Kconfig

@@ -23,6 +23,11 @@ config ARMV7M_DCACHE
 	default n
 	depends on ARMV7M_HAVE_DCACHE
 
+config ARMV7M_DCACHE_WRITETHROUGH
+	bool "D-Cache Write-Through"
+	default n
+	depends on ARMV7M_DCACHE
+
 config ARMV7M_HAVE_ITCM
 	bool
 	default n

arch/arm/src/armv7-m/arch_clean_dcache.c

@@ -46,7 +46,7 @@
 
 #include "cache.h"
 
-#ifdef CONFIG_ARMV7M_DCACHE
+#if defined(CONFIG_ARMV7M_DCACHE) && !defined(CONFIG_ARMV7M_DCACHE_WRITETHROUGH)
 
 /****************************************************************************
  * Pre-processor Definitions
@@ -146,4 +146,4 @@ void arch_clean_dcache(uintptr_t start, uintptr_t end)
   ARM_ISB();
 }
 
-#endif  /* CONFIG_ARMV7M_DCACHE */
+#endif  /* CONFIG_ARMV7M_DCACHE && !CONFIG_ARMV7M_DCACHE_WRITETHROUGH */

arch/arm/src/armv7-m/arch_clean_dcache_all.c

@@ -46,7 +46,7 @@
 
 #include "cache.h"
 
-#ifdef CONFIG_ARMV7M_DCACHE
+#if defined(CONFIG_ARMV7M_DCACHE) && !defined(CONFIG_ARMV7M_DCACHE_WRITETHROUGH)
 
 /****************************************************************************
  * Pre-processor Definitions
@@ -126,4 +126,4 @@ void arch_clean_dcache_all(void)
   ARM_ISB();
 }
 
-#endif  /* CONFIG_ARMV7M_DCACHE */
+#endif  /* CONFIG_ARMV7M_DCACHE && !CONFIG_ARMV7M_DCACHE_WRITETHROUGH */

arch/arm/src/armv7-m/arch_flush_dcache.c

@@ -46,7 +46,7 @@
 
 #include "cache.h"
 
-#ifdef CONFIG_ARMV7M_DCACHE
+#if defined(CONFIG_ARMV7M_DCACHE) && !defined(CONFIG_ARMV7M_DCACHE_WRITETHROUGH)
 
 /****************************************************************************
  * Pre-processor Definitions
@@ -146,4 +146,4 @@ void arch_flush_dcache(uintptr_t start, uintptr_t end)
   ARM_ISB();
 }
 
-#endif  /* CONFIG_ARMV7M_DCACHE */
+#endif  /* CONFIG_ARMV7M_DCACHE && !CONFIG_ARMV7M_DCACHE_WRITETHROUGH */

arch/arm/src/armv7-m/arch_flush_dcache_all.c

@@ -46,7 +46,7 @@
 
 #include "cache.h"
 
-#ifdef CONFIG_ARMV7M_DCACHE
+#if defined(CONFIG_ARMV7M_DCACHE) && !defined(CONFIG_ARMV7M_DCACHE_WRITETHROUGH)
 
 /****************************************************************************
  * Pre-processor Definitions
@@ -125,4 +125,4 @@ void arch_flush_dcache_all(void)
   ARM_ISB();
 }
 
-#endif  /* CONFIG_ARMV7M_DCACHE */
+#endif  /* CONFIG_ARMV7M_DCACHE && !CONFIG_ARMV7M_DCACHE_WRITETHROUGH */

arch/arm/src/armv7-m/cache.h

@@ -211,6 +211,31 @@ static inline void arch_invalidate_icache_all(void)
 #endif
 }
 
+/****************************************************************************
+ * Name: arch_dcache_writethrough
+ *
+ * Description:
+ *   Configure the D-Cache for Write-Through operation.
+ *
+ * Input Parameters:
+ *   None
+ *
+ * Returned Value:
+ *   None
+ *
+ ****************************************************************************/
+
+#if defined(CONFIG_ARMV7M_DCACHE) && defined(CONFIG_ARMV7M_DCACHE_WRITETHROUGH)
+static inline void arch_dcache_writethrough(void)
+{
+  uint32_t regval = getreg32(NVIC_CACR);
+  regval |= NVIC_CACR_FORCEWT;
+  putreg32(regval, NVIC_CACR);
+}
+#else
+#  define arch_dcache_writethrough()
+#endif
+
 /****************************************************************************
  * Public Variables
  ****************************************************************************/
@@ -322,6 +347,9 @@ void arch_invalidate_dcache_all(void);
  *   Clean the data cache within the specified region by flushing the
  *   contents of the data cache to memory.
  *
+ *   NOTE: This operation is un-necessary if the DCACHE is configured in
+ *   write-through mode.
+ *
  * Input Parameters:
  *   start - virtual start address of region
  *   end   - virtual end address of region + 1
@@ -336,7 +364,7 @@ void arch_invalidate_dcache_all(void);
  *
  ****************************************************************************/
 
-#ifdef CONFIG_ARMV7M_DCACHE
+#if defined(CONFIG_ARMV7M_DCACHE) && !defined(CONFIG_ARMV7M_DCACHE_WRITETHROUGH)
 void arch_clean_dcache(uintptr_t start, uintptr_t end);
 #else
 #  define arch_clean_dcache(s,e)
@@ -349,6 +377,9 @@ void arch_clean_dcache(uintptr_t start, uintptr_t end);
  *   Clean the entire data cache within the specified region by flushing the
  *   contents of the data cache to memory.
  *
+ *   NOTE: This operation is un-necessary if the DCACHE is configured in
+ *   write-through mode.
+ *
  * Input Parameters:
  *   None
  *
@@ -362,7 +393,7 @@ void arch_clean_dcache(uintptr_t start, uintptr_t end);
  *
  ****************************************************************************/
 
-#ifdef CONFIG_ARMV7M_DCACHE
+#if defined(CONFIG_ARMV7M_DCACHE) && !defined(CONFIG_ARMV7M_DCACHE_WRITETHROUGH)
 void arch_clean_dcache_all(void);
 #else
 #  define arch_clean_dcache_all()
@@ -375,6 +406,9 @@ void arch_clean_dcache_all(void);
  *   Flush the data cache within the specified region by cleaning and
  *   invalidating the D cache.
  *
+ *   NOTE: If DCACHE write-through is configured, then this operation is the
+ *   same as arch_invalidate_cache().
+ *
  * Input Parameters:
  *   start - virtual start address of region
  *   end   - virtual end address of region + 1
@@ -390,7 +424,11 @@ void arch_clean_dcache_all(void);
  ****************************************************************************/
 
 #ifdef CONFIG_ARMV7M_DCACHE
+#ifdef CONFIG_ARMV7M_DCACHE_WRITETHROUGH
+#  define arch_flush_dcache(s,e) arch_invalidate_dcache(s,e)
+#else
 void arch_flush_dcache(uintptr_t start, uintptr_t end);
+#endif
 #else
 #  define arch_flush_dcache(s,e)
 #endif
@@ -401,6 +439,9 @@ void arch_flush_dcache(uintptr_t start, uintptr_t end);
  * Description:
  *   Flush the entire data cache by cleaning and invalidating the D cache.
  *
+ *   NOTE: If DCACHE write-through is configured, then this operation is the
+ *   same as arch_invalidate_cache_all().
+ *
  * Input Parameters:
  *   None
  *
@@ -415,7 +456,11 @@ void arch_flush_dcache(uintptr_t start, uintptr_t end);
  ****************************************************************************/
 
 #ifdef CONFIG_ARMV7M_DCACHE
+#ifdef CONFIG_ARMV7M_DCACHE_WRITETHROUGH
+#  define arch_flush_dcache_all() arch_invalidate_dcache_all()
+#else
 void arch_flush_dcache_all(void);
+#endif
 #else
 #  define arch_flush_dcache_all()
 #endif

arch/arm/src/samv7/Kconfig

@@ -117,6 +117,15 @@ config SAMV7_HAVE_EBI
 config SAMV7_EMAC
 	bool
 	default n
+	select ARMV7M_DCACHE_WRITETHROUGH if ARMV7M_DCACHE
+	---help---
+		NOTE that write-through caching is automatically selected.  This is
+		to work around issues with the RX and TX descriptors with are 8-bits
+		in size.  But the D-Cache cache line size is 32-bytes.  That means
+		that you cannot reload, clean or invalidate a descriptor without also
+		effecting three neighboring desciptors.  Setting write through mode
+		eliminates the need for cleaning.  If only reloading and invalidating
+		are done, then there is no problem.
 
 config SAMV7_HSMCI
 	bool

arch/arm/src/samv7/Make.defs

@@ -66,9 +66,11 @@ endif
 
 ifeq ($(CONFIG_ARMV7M_DCACHE),y)
 CMN_CSRCS += arch_enable_dcache.c arch_disable_dcache.c
+CMN_CSRCS += arch_invalidate_dcache.c arch_invalidate_dcache_all.c
+ifneq ($(CONFIG_ARMV7M_DCACHE_WRITETHROUGH),y)
 CMN_CSRCS += arch_clean_dcache.c arch_clean_dcache_all.c
 CMN_CSRCS += arch_flush_dcache.c arch_flush_dcache_all.c
-CMN_CSRCS += arch_invalidate_dcache.c arch_invalidate_dcache_all.c
+endif
 endif
 
 ifeq ($(CONFIG_ARCH_FPU),y)

arch/arm/src/samv7/sam_start.c

@@ -380,6 +380,7 @@ void __start(void)
 
   /* Enable I- and D-Caches */
 
+  arch_dcache_writethrough();
   arch_enable_icache();
   arch_enable_dcache();
 

configs/samv71-xult/README.txt

@@ -105,6 +105,12 @@ The BASIC nsh configuration is fully function (as desribed below under
        At -O2, many packets can be exchanged but eventually there is a
        hardfault, presumably because of a misdirected DMA.
 
+     I have no hard evidence, but I believe that the nature of the problem
+     related to fact that each descriptor in the arrays are 8-bytes each,
+     but cache operations are performed on 32-byte memory chunks.  So it is
+     impossible to clean or invalidate a single descriptor without also
+     cleaning or invalidaing adjacent descriptors.
+
   7. The USBHS device controller driver (DCD) is complete but non-functional.
      At this point, work has stopped because I am stuck.  The problem is that
      bus events are not occurring:  Nothing is detected by the USBHS when the
@@ -117,9 +123,7 @@ The BASIC nsh configuration is fully function (as desribed below under
      sample code and study of the data sheet, but I have not found the key to
      solving this.
 
-     - I need to try this as -O2 optimization as well.
++nmnmSerial Console
-
-Serial Console
 ==============
 
 The SAMV71-XULT has no on-board RS-232 drivers so it will be necessary to
@@ -767,6 +771,12 @@ NOTES:
      System Type -> Toolchain:
        CONFIG_ARMV7M_TOOLCHAIN_GNU_EABIW=y : GNU ARM EABI toolchain
 
+     NOTE: As of this writing, there are issues with using this tool at
+     the -Os level of optimization.  This has not been proven to be a
+     compiler issue (as least not one that might not be fixed with a
+     well placed volatile qualifier).  However, in any event, it is
+     recommend that you use not more that -O2 optimization.
+
 Configuration sub-directories
 -----------------------------