MCF5484 and MMU initialisation

[schiller]

Hi all,

I have a custom MCF5484 board with 128Mb RAM. My development environnement is :

- U-Boot

- Linux 2.6.10

- gcc version 4.2.3 (Sourcery G++ Lite 4.2-125)

Under U-Boot, I'm able to see and use the whole 128Mb.

CONFIG_SDRAM_SIZE is set to 0x8000000 in the Linux configuration. Linux starts with 128Mb (displayed at boot time). When /sbin/init is called, the system freezes. I tried to change the configuration of the MMU in head.S but nothing has changed.

I read that the TLB of the MCF5484 has 32 lines of 1Mb leading to use no more than 32Mb with the MMU.

So, my question is : is there a possibility to use the whole RAM I have on my board (128Mb) with the MCF5484 and the MMU ?

If not, why am I able to use the 5485EVB board with 64Mb of RAM (2.6.25 Linux kernel) ?

Thanks for your help!

[fsl_linux_spt]

I am not aware of any limitations for this.  Have you tried running the 2.6.25 kernel on your board to see if that behaves any differently?

[schiller]

No, I did not try to run the 2.6.25 kernel. I manage to get my board working with the full 128Mb by merging the head.S files of those two kernels (2.6.10 and 2.6.25).

I'm a newbie with MMU based board and I'm still trying to understand why Linux is able to see 128Mb whereas I only map 32Mb of the memory. In other words, how the others 96Mb are used and why are they available? 

I guess this question might be  stupid but I need to understand :smileyhappy:.

Thanks for your help!