[U-Boot-Users] UNCACHED_SDRAM macro issue

[Shinya Kuribayashi <skuribay@ruby.dti.ne.jp>]

Shinya Kuribayashi wrote:
> Shinya Kuribayashi wrote:
>>> I think that on my application the UNCACHED_SDRAM should map the address
>>> on KSEG1 (how it is now) but this simply doesn't work. Instead, using
>>> the PHYSADDR(a) macro... the kernel is able to start.
>>>
>>> I suspect that there are issues on cache management. Can be? 
>> IMHO it's not related to cache.
> 
> How do you set ERL and EXL bits? Please try to clear them at the
> STATUS register initialization like:
> 
>  reset:
>         <snip>
> 
>         /* STATUS register */
>         mfc0    k0, CP0_STATUS
> -       li      k1, ~ST0_IE
> +       li      k1, ~(ST0_ERL | ST0_EXL | ST0_IE)
>         and     k0, k1
>         mtc0    k0, CP0_STATUS
> 
> ERL and EXL disable exceptions. Due to this spec, we are in danger
> of overlooking something critical. If this change brings in new
> exception(s), please fix the causes of them first. Hope this helps.

Err, sorry for confusing example. Here's the right one:

diff --git a/cpu/mips/start.S b/cpu/mips/start.S
index c92b162..02797f7 100644
--- a/cpu/mips/start.S
+++ b/cpu/mips/start.S
@@ -211,14 +211,20 @@ reset:
 	mtc0	zero, CP0_WATCHLO
 	mtc0	zero, CP0_WATCHHI
 
+	/* Inhibit deffered WATCH exception */
+	mfc0	k0, CP0_CAUSE
+	li	k1, ~(1UL << 22)	# CP0.Cause.WP = 0
+	and     k0, k0, k1
+	mtc0	k0, CP0_CAUSE
+
 	/* STATUS register */
 #ifdef  CONFIG_TB0229
 	li	k0, ST0_CU0
 #else
 	mfc0	k0, CP0_STATUS
 #endif
-	li	k1, ~ST0_IE
-	and	k0, k1
+	ori	k0, (ST0_ERL | ST0_EXL | ST0_IE)
+	xori	k0, (ST0_ERL | ST0_EXL)
 	mtc0	k0, CP0_STATUS
 
 	/* CAUSE register */

Again, it's highy recommended to make sure U-Boot works fine under
interrupts enabled (CP0.Status.IE=1), before digging into UNCACHED_
SDRAM problem.

  Shinya