[U-Boot-Users] MPC85xx: Question about Local Bus initialization

[Jens Gehrlein <sew_s@tqs.de>]

Hi Clemens,

thanks for the reply.


Clemens Koller schrieb:
>  > Hi,
>  >
>  > I took a look into the files board/mpc8560ads.c and board/tqm85xx.c and
>  > found something strange:
>  >
>  > 1. In the function local_bus_init() the current CLKDIV is read from the
>  > register LCRR as was set by Hardreset. After that, the decision is made,
>  > wether the DLL has to be enabled/disabled/overridden. Inside the if-else
>  > blocks the new CLKDIV is changed. But IMO the CLKDIV has to be set
>  > before the query.
>  >
>  > This is the current code:
>  >     clkdiv = lbc->lcrr & 0x0f;
>  >     lbc_hz = sysinfo.freqSystemBus / 1000000 / clkdiv;
>  >
>  >     if (lbc_hz < 66) {
>  >         lbc->lcrr = CFG_LBC_LCRR | 0x80000000;    /* DLL Bypass */
>  >
>  >     } else if (lbc_hz >= 133) {
>  >         lbc->lcrr = CFG_LBC_LCRR & (~0x80000000); /* DLL Enabled
>  >     ...
>  > This may be the situation on other 85xx boards, too. I didn't check them
>  > all.
>  > What was the intention, DLL modification dependent on the clock set by
>  > the MPC at hardreset or dependent on the targeted frequency?
> 
> MPC8540 Reference Manual, Page 13-23, LCRR Field Descriptions:
> "DLL bypass. This bit should be set when using low bus clock
> frequencies if the DLL is unable to lock. When in DLL bypass mode,
> incoming data is captured in the middle of the bus clock cycle."

> 
> Usually 85xx boot from Flash connected to the Local Bus, so the bootstrap
> configuration out of a hard reset need to be correct at first place.
> Then, if the bootloader (or later, the kernel) wants to (re-)set it
> during runtime, it also has to set the DLL enable bit depending on the
> desired target frequency.
But the bootloader should not itself pull the rug out from under its 
feet. As I see, the U-Boot works if I change the frequency during 
runtime (changed define CFG_LBC_LCRR). Does anybody know why?
In our Monitor MON85XX we don't change the frequency in flash code, but 
later in RAM code according to the target frequency. Additionally 
LCRR[EADC] and OR[EAD] are modified if the target frequency is greater 
than 83 MHz according to the HW developer's timing calculations.

Regards,
Jens