On Tuesday 09 June 2009, David Brownell wrote: > For some reason the AT91rm9200 lowlevel init writes to a bunch of > reserved or read-only addresses. All the boards seem to define the > value-to-be-written values as zero ... but they shouldn't actually > be writing *anything* there.
Repeat: should not write to reserved or read-ony addresses. > If there's a real need to write these locations, like an erratum > that's not included in the current list, that should be reflected > in a source code comment. Looks like maybe some very early BDI-2000 > setup code has been carried along by cargo cult programming since > at least late 2004 (per GIT history). > > Meanwhile, here's a patch/RFC disabling what seems to be bogosity. > If it's eventually a "go", the supporting code should be removed. No comments? > --- > cpu/arm920t/at91rm9200/lowlevel_init.S | 10 ++++++++-- > 1 file changed, 8 insertions(+), 2 deletions(-) > > --- a/cpu/arm920t/at91rm9200/lowlevel_init.S > +++ b/cpu/arm920t/at91rm9200/lowlevel_init.S > @@ -81,6 +81,7 @@ LoopOsc: > bne 0b > /* delay - this is all done by guess */ > ldr r0, =0x00010000 > + /* (vs reading PMC_SR for LOCKA, LOCKB ... or MOSCS earlier) */ > 1: > subs r0, r0, #1 > bhi 1b > @@ -108,16 +109,22 @@ LoopOsc: > .ltorg > > SMRDATA: > +#if 0 > +/* MC_PU* are reserved "do not use" memory controller addresses; > + * see table 16-1 of the rm9200 manual > + */ > .word AT91C_MC_PUIA > .word CONFIG_SYS_MC_PUIA_VAL > .word AT91C_MC_PUP > .word CONFIG_SYS_MC_PUP_VAL > .word AT91C_MC_PUER > .word CONFIG_SYS_MC_PUER_VAL > +/* MC_ASR/AASR are read-only registers, see table 16-1 again */ > .word AT91C_MC_ASR > .word CONFIG_SYS_MC_ASR_VAL > .word AT91C_MC_AASR > .word CONFIG_SYS_MC_AASR_VAL > +#endif > .word AT91C_EBI_CFGR > .word CONFIG_SYS_EBI_CFGR_VAL > .word AT91C_SMC_CSR0 > @@ -128,8 +135,7 @@ SMRDATA: > .word CONFIG_SYS_PLLBR_VAL > .word AT91C_MCKR > .word CONFIG_SYS_MCKR_VAL > - /* SMRDATA is 80 bytes long */ > - /* here there's a delay of 100 */ > + /* here there's a delay */ > SMRDATA1: > .word AT91C_PIOC_ASR > .word CONFIG_SYS_PIOC_ASR_VAL > _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
