[U-Boot-Users] asynchronous clocking mode for arm920t

[Steven Scholz]

Hi all,

( was: [U-Boot-Users] [PATCH 4/4] add csb637 (at91rm9200) support )

I wrote:

 >> this patch switches the at91rm9200 to synchronous clock mode after
 >> initialization (it would otherwise stay in FastBus mode which is
 >> the _slowest_ clock mode).
 >
 > But I thought FastBus mode is the prefered setting for ARM cpus.

Now I retract the above statement and claim the oposite! ;-)

Anders' is correct. Atmel support told me a year ago
"Linux uses the Asynchronous mode."
With his patch I now get 79.87 BogoMIPS again (without less the 40).

So I helps for AT91RM9200.

But I don't see something similar for my i.MX ARM9 and still this on in 
running as fast as expected...
The reason ist that this setting is done in board/mx1fs2/lowlevel_init.S and 
board/scb9328/lowlevel_init.S.

So I'd say the asynchronous clocking mode is best for all arm920t cpus and 
thus maybe this is the better patch:

Index: u-boot/cpu/arm920t/start.S
===================================================================
RCS file: /cvsroot/u-boot/u-boot/cpu/arm920t/start.S,v
retrieving revision 1.13
diff -u -r1.13 start.S
--- u-boot/cpu/arm920t/start.S  5 Apr 2005 22:30:51 -0000       1.13
+++ u-boot/cpu/arm920t/start.S  4 May 2005 11:27:35 -0000
@@ -246,13 +246,14 @@
         mcr     p15, 0, r0, c8, c7, 0   /* flush v4 TLB */

         /*
-        * disable MMU stuff and caches
+        * disable MMU stuff and caches, switch to Asynchronous Clocking Mode
          */
         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
+       orr     r0, r0, #0xC0000000     @ set bit 31 (iA) and 30 (nF)
         mcr     p15, 0, r0, c1, c0, 0

Can someone comment on the s3c24x0 cpu?

--
Steven