[U-Boot-Users] BRGs on ep8248 after updating CLKIN

[Alan Bennett]

Ok, I don't know what I was thinking.  Yes, it's 66 MHz.

The only thing I can see is in the calculation for BUS_CLK
      speed.c   =   gd->bus_clk = clkin;

However, looking at the Ref Manual for the 8272, Figure 10-1,
   It shows a conflict:
        1. MAIN_PLL = 66MHz * (SCMR[pllmf]+1) = 66MHz*(5+1) = 396 MHz
        2. BUSCLK = MAIN_PLL/(SCMR[busdf]+1) = 396MHz /(3+1) = 99 MHz
        and then
        BUS_CLK = SCMR[corecnf] multiplier 1E=3.5*BUS_CLK

BUT CLKIN != BUS_CLK  (66MHz != 99MHz)

So could it be
		gd->cpu_clk = (gd->bus_clk * cp->b2c_mult) / 2;
instead of
		gd->cpu_clk = (clkin * cp->b2c_mult) / 2;

-Alan

On 11/29/07, Jerry Van Baren <gerald.vanbaren at ge.com> wrote:
> Alan Bennett wrote:
> > When I originally supported my ep8248-style board, I had
> > #define CONFIG_8260_CLKIN     66000000        /* in Hz */
> >
> > However, I noticed (after far too much time had passed) that my cpu
> > speed wasn't matching my expectations.  (reported 230 MHz, and
> > expected 350 MHz).
> >
> > This was rather easily fixed by changing the CONFIG_8260_CLKIN to 100 MHz:
> > #define CONFIG_8260_CLKIN     100000000       /* in Hz */
> >
> > However, my BRGs / SMC1 uart is now broke(baud-rate mismatch).  Does
> > anyone have experience with this section of u-boot that could help me
> > out?
> >
> > My BRG7 is configured by u-boot(1.3+) = 0x00010078 ~ CD = 60 (0x3c).
> > And there is an apparent baud-rate mismatch and all the output is
> > garbled now.  (with a scope I measured ~ 25.5 / 26 K, when I'm
> > expecting 38.4k)
> >
> > I think I'm missing something in the equation, but I'm not sure where
> > it is.  If I simply update the CD to be 162 (162*38400*16 = 99,532,800
> > ~ 100 MHz) the serial port is still dead.
> >
> > Any ideas?
>
> Hi Alan,
>
> I suspect that your clock is really 66MHz (read it off the crystal, that
> is the definitive authority).  Generally BRGs don't lie - if your
> CONFIG_8260_CLKIN doesn't match the actual crystal, your baud rate is
> going to be wrong.  Your baud rate is right when CONFIG_8260_CLKIN is
> set to 66MHz and wrong when set to 100MHz - pretty strong evidence.
>
> My theory is that your crystal is 66MHz but your CPU multiplier is
> misconfigured.  In the 8260 the CPU multiplier is selected by the HRCW
> (MODCK_H) _and_ some physical pins on the CPU (MODCK[1-3]) - your 8248
> may be different.
>
> HTH,
> gvb
>