[U-Boot-Users] Bug in AT91RM9200: icache not enabled!

Steven Scholz steven.scholz at imc-berlin.de
Sun Mar 13 15:03:05 CET 2005

Hi there,

while finding out why the loading of my FPGA takes so long with the latest CVS 
version of U-Boot I noticed that the icache for the AT91RM9200 is not enabled 
although icache_enable() is called in cpu/at91rm9200/start.S:

          * This does a lot more than just set up the memory, which
          * is why it's called lowlevelinit
         bl      lowlevelinit /* in memsetup.S */
         bl      icache_enable;
         mrc     p15, 0, r0, c1, c0, 0
         /* Reset bit :Little Endian end fast bus mode */
         ldr     r3, =0xC0000080
         /* Set bit :Asynchronous clock mode, Not Fast Bus */
         ldr     r4, =0xC0000000
         bic     r0, r0, r3
         orr     r0, r0, r4
         /* write r0 in cp15 control register (cp15 r1) */
         mcr     p15, 0, r0, c1, c0, 0

The problem is that icache_enable() only works on bit 2 of CP15 Reg 1. But the 
important bit seems to be bit 12 judging by the AT91RM9200 User Manual page 49.

Looking at cpu/arm920t/start.S reveals that bit 12 is set:

          * disable MMU stuff and caches
         mrc     p15, 0, r0, c1, c0, 0
         bic     r0, r0, #0x00002300     @ clear bits 13, 9:8 (--V- --RS)
         bic     r0, r0, #0x00000087     @ clear bits 7, 2:0 (B--- -CAM)
         orr     r0, r0, #0x00000002     @ set bit 2 (A) Align
 >>>>    orr     r0, r0, #0x00001000     @ set bit 12 (I) I-Cache
         mcr     p15, 0, r0, c1, c0, 0

So my suggestion is using the above code from cpu/arm920t/start.S for the 
AT91RM9200 for consistency in the ARM directories. Explicitly disabling MMU 
would not harm. And maybe explicitly enabling "Alignment Fault" would be a good 
thing as well.

And maybe we should even fix the functions dcache_{en,dis}able() and 
icache_{en,dis}able() in cpu/at91rm9200/cpu.c by introducing

-#define C1_IDC          (1<<2)  /* icache and/or dcache off/on */
+#define C1_DC           (1<<2)  /* dcache off/on */
+#define C1_IC           (1<<1)  /* icache off/on */

just like in cpu/arm920t/cpu.c.

Please comment on this. I am willing to sent appropriate patches.

Thanks a million!


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