Nios II 中的缓存和内存数据的读写

nios 使用地址中31bit来表示访问是否bypass cache。
如果bit 31=0 表示不bypass cache，即使用cache里的数据；如果bit 31=1表示bypass cache，即直接使用mem中的数据。
如alt_remap_uncached函数

 1 #ifdef NIOS2_MMU_PRESENT
 2 /* Convert KERNEL region address to IO region address */
 3 #define BYPASS_DCACHE_MASK   (0x1 << 29)
 4 #else
 5 /* Set bit 31 of address to bypass D-cache */
 6 #define BYPASS_DCACHE_MASK   (0x1 << 31)
 7 #endif
 8
 9 /*
10  * Convert a pointer to a block of cached memory, into a block of
11  * uncached memory.
12  */
13
14 volatile void* alt_remap_uncached (void* ptr, alt_u32 len)
15 {
16   alt_dcache_flush (ptr, len);
17   return (volatile void*) (((alt_u32) ptr) | BYPASS_DCACHE_MASK);
18 }

其中

 1 #ifdef NIOS2_FLUSHDA_SUPPORTED
 2 #define ALT_FLUSH_DATA(i) __asm__ volatile ("flushda (%0)" :: "r" (i));
 3 #else
 4 #define ALT_FLUSH_DATA(i) __asm__ volatile ("flushd (%0)" :: "r" (i));
 5 #endif /* NIOS2_FLUSHDA_SUPPORTED */
 6
 7 /*
 8  * alt_dcache_flush() is called to flush the data cache for a memory
 9  * region of length "len" bytes, starting at address "start".
10  *
11  * Any dirty lines in the data cache are written back to memory.
12  */
13
14 void alt_dcache_flush (void* start, alt_u32 len)
15 {
16 #if NIOS2_DCACHE_SIZE > 0
17
18   char* i;
19   char* end;
20
21   /*
22    * This is the most we would ever need to flush.
23    *
24    * SPR 196942, 2006.01.13: The cache flush loop below will use the
25    * ‘flushda‘ instruction if its available; in that case each line
26    * must be flushed individually, and thus ‘len‘ cannot be trimmed.
27    */
28   #ifndef NIOS2_FLUSHDA_SUPPORTED
29   if (len > NIOS2_DCACHE_SIZE)
30   {
31     len = NIOS2_DCACHE_SIZE;
32   }
33   #endif
34
35   end = ((char*) start) + len;
36
37   for (i = start; i < end; i+= NIOS2_DCACHE_LINE_SIZE)
38   {
39     ALT_FLUSH_DATA(i);
40   }
41
42   /*
43    * For an unaligned flush request, we‘ve got one more line left.
44    * Note that this is dependent on NIOS2_DCACHE_LINE_SIZE to be a
45    * multiple of 2 (which it always is).
46    */
47
48   if (((alt_u32) start) & (NIOS2_DCACHE_LINE_SIZE - 1))
49   {
50     ALT_FLUSH_DATA(i);
51   }
52
53 #endif /* NIOS2_DCACHE_SIZE > 0 */
54 }