Index: firmware/target/arm/system-pp502x.c
===================================================================
--- firmware/target/arm/system-pp502x.c	(revision 31026)
+++ firmware/target/arm/system-pp502x.c	(working copy)
@@ -209,6 +209,15 @@
     GPIOL_INT_EN        = 0;
 }
 
+/* FIXME: The following bug may not be present on all PP502x variants.
+ * The workaround code wastes time and energy when the bug is not present. */
+
+/* When the cache is flushed or flushed and invalidated, cache lines
+ * which are not marked as valid can cause memory corruption. Therefore,
+ * all cache lines must be marked as valid before calling these functions.
+ * This is accomplished via code that runs after cache initialization and
+ * invalidation. */
+
 void ICODE_ATTR cpucache_commit(void)
 {
     if (CACHE_CTL & CACHE_CTL_ENABLE)
@@ -224,9 +233,23 @@
 {
     if (CACHE_CTL & CACHE_CTL_ENABLE)
     {
+        /* Interrupts between the flush and rewriting of cache
+         * status words could cause memory corruption. */
+        register int istat = disable_interrupt_save(IRQ_FIQ_STATUS);
+        
         CACHE_OPERATION |= CACHE_OP_FLUSH | CACHE_OP_INVALIDATE;
         while ((CACHE_CTL & CACHE_CTL_BUSY) != 0);
         nop; nop; nop; nop;
+
+        /* Point all cache status words past end of RAM, 
+         * and make them valid, but not dirty. */
+        register volatile unsigned long *p;
+        for (p = &CACHE_STATUS_BASE;
+             p < (&CACHE_STATUS_BASE) + 512*16/sizeof(*p);
+             p += 16/sizeof(*p))
+            *p = ((8*0x100000) >> 11) | 0x800000;
+
+        restore_interrupt(istat);
     }
 }
 void cpucache_invalidate(void) __attribute__((alias("cpucache_commit_discard")));
@@ -257,6 +280,13 @@
     /* enable cache */
     CACHE_CTL |= CACHE_CTL_INIT | CACHE_CTL_ENABLE | CACHE_CTL_RUN;
     nop; nop; nop; nop;
+
+    /* Ensure all cache lines are valid for the next flush. Since this
+     * can run from cached RAM, rewriting of cache status words may not
+     * be safe and the cache is filled instead by reading. */
+    register volatile char *p;
+    for (p = (volatile char *)0; p < (volatile char *)0x2000; p += 0x10)
+        (void)*p;
 }
 #endif /* BOOTLOADER || HAVE_BOOTLOADER_USB_MODE */