AW: [U-Boot-Users] MPC5200 XLB / IP Frequencies

[Jonas Mark (ST/EPP1) *]

Mats,

> we are using u-boot on the MPC5200. 
> In the file "cpu_init.c" there is a comment: "Motorola
> reports IPB better run at 133MHz". 
> Does anyone know where this information can be found? 
> I tried to find a note in the errata (Rev 5 10/2004)
> but found the following in support ID 412: 
> "Use the clock ratio XLB : IP = 2 : 1" - and with XLB
> running at maximum 132MHz it contradicts 
> the statement that IP runs better at 133MHz. 
>
>Has anyone any ideas about how this mix together? 

1) Freescale recommends running IPBI at 133 MHz because that gives
better performance.

2) Errata ID 412 tells you that if you make an simultaneous access to
the Local Plus Bus using the CPU and BestComm you can end up in an TEA
or ChkStop. This can we worked around by setting XLB:IPBI to 2:1.

If you combine these two statements it means that you can get better
performance when running IPBI at 133 MHz (i.e. XLB:IPBI = 1:1) as long
as you do not run a BestComm task accessing Local Plus in parallel with
Local Plus accesses of the CPU. AFAIK none of the existing Linux drivers
utilizes BestComm to access a Local Plus device.

=> IPBI at 133 MHz should be safe.

Regards
Mark Jonas