[ECOS] Porting eCos to DDB-VRC4375(Memory mapping)

Ling Su lingsu@palmmicro.com
Mon Jan 29 18:19:00 GMT 2001

I am working on porting eCos to DDB-VRC4375 based on VRC4373 source code. Of
course, if I make a working version, I will let you know. Now I have several
questions on the memory mapping.

The DDB-VRC4375 contains 32M SDRAM, but DDB-VRC4373 has 8M SDRAM.

<1>. In the mlt_mips_vr4300_vrc4373_ram.ldi,
    ram : ORIGIN = 0x80100000, LENGTH = 0x500000

I am wondering why the LENGTH is 0x500000 instead of 0x700000. For vrc4375
is SDRAM is 32M, how should I set it.  I first set it to 0x1E00000, I am not
sure if it is right. Any explaination on the LENGTH will be welcomed a lot.

<2>. In the mlt_mips_vr4300_vrc4373_rom.ldi,
    ram: ORIGIN = 0x80000800, LENGTH = 0x7F800
    rom: ORIGIN = 0xBFC0000, LENGTH = 0x80000
I don't quite understand the ram LENGTH setting, why we just use 512KB ram
in rom start up setting? Can we set the ram LENGTH to larger. Another thing
is why its ORIGIN is 0x80000800?

<3>. What is ROMRAM startup type? I found the memory mapping for ROMRAM is
the same as RAM startup type, why?

I am working on making the GDB stubs for the DDB-VRC4375, since the vrc4375
has a FLASH ROM, so I can modify it a lot of times. But now I still didn't
make a GDB working. I think if I can make a RAM startup type GDB stub
working with my PMON, It will be convenient to try it. But the PMON in
VRC4375 Base Memory physical address 0x00000000 - 0x1FFFFFF mapped to both
0x80000000 to 0x81FFFFFF and 0xA0000000 to 0xA1FFFFFF, two regions. I don't
know how it happend. In the PMON, I found the user space is from 0xA010000
to above. Can anyone kindly shed some light on how to map two virtual region
to one physical region?

Thanks a lot!


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