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

Steven Scholz steven.scholz at imc-berlin.de
Sun Mar 13 16:40:18 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;
>    ...
> 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.

I am a bit confused right now! The function

void icache_enable(void)
     ulong reg;
     reg = read_p15_c1();
     reg |= C1_IC;

from cpu/at91rm9200/cpu.c does not seem to work (at least when called from 
start.S). When I do

  mrc     p15, 0, r0, c1, c0, 0	@ read cp15 control register (cp15 r1) in r0
  orr	r0, r0, #0x00001000	@ set bit 12 (I) I-Cache
  mcr     p15, 0, r0, c1, c0, 0	@ write r0 in cp15 control register (cp15 r1)

which should be the same, it works ... :-(

Especially I dont understand why the C function would need a cp_delay() why the 
assembler code does not ...


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