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 | | From: | manan.kathuria at gmail.com | | Subject: | boot code works when it shudnt (newbie) | | Date: | 11 Jan 2005 01:00:54 -0800 |
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 | hi
iv been working on a project involving AT91RM9200 and i got some basic
boot code that sets it up etc etc . part of the code sets up the slow
clock as the master by first switching from "whatever" mode to PLLB and
then from PLLB to slowclock . if u taka a look at the code
ldr r1, = AT91C_BASE_PMC ; Get the PMC Base Address
;------------------------------------------------------------------------------
;-Write in the MCKR dirty value concerning the clock selection CSS then
overwrite it in a second sequence
;------------------------------------------------------------------------------
;
;-Master Clock Register PMC_MCKR : "dirty CSS" is selected
ldr r0, = AT91C_PMC_CSS_PLLB_CLK
str r0, [r1, #PMC_MCKR]
;- Reading the PMC Status register to detect when the Master Clock is
commuted
mov r4, #0x8
MCKR_Loop
ldr r3, [r1, #PMC_SR]
and r3, r4, r3
cmp r3, #0x8
bne MCKR_Loop
ya , so nowhere here is the pllar register configured . the system
starts from reset and so the DIVA bit is set to 0 which means PLL
output is 0 . so there shd be no clock once the clock is switchd to
PLLB and the system shd stall , but AMAZINGLY , it works! what the hell
is going on????
thanks in advance
Mnn!
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| | From: | Mayank Kaushik | | Subject: | Re: boot code works when it shudnt (newbie) | | Date: | 11 Jan 2005 12:21:02 -0800 |
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| But as you may see that later in the code, we select the slow clock
among the options available in the master clock generator. From the
block diagram of the PMC, we can see that the processor wil still get
the clock, regardless of whether the plls are revved up or not.
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| | From: | Mayank Kaushik | | Subject: | Re: boot code works when it shudnt (newbie) | | Date: | 11 Jan 2005 12:34:25 -0800 |
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| More inportantly, check the waveforms on pg 268. ul see that the
processor stays on the same clock till mckrdy is asserted. then it
should latch on to the pll, but we load it with a new value in the
code...Though i dont think all this has to be done..
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