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Newbie STPC question
- From: ntjunkie at boltblue dot net
- To: ecos-discuss at sources dot redhat dot com
- Date: Wed, 18 Sep 2002 14:48:34 +0100 (BST)
- Subject: [ECOS] Newbie STPC question
Hi,
I am currently trying to get eCos to work on an ST Microelectronics STPC.
It is pretty much an PC system on chip, with a 486 core.
I am not using a bios, but some vendor bootloader code which 'warm starts' the
chip (DRAM refresh / peripheral initialization etc).
After initialization, the bootloader code copies and runs a secondary
bootloader (which could be the eCos O/S if small enough to fit in the F block),
either in protected mode or real mode. Depends on the option.
When the bootloader code copies and jumps to the secondary bootloader, it
leaves the system in the following state:
Protected-mode:
CS: set to 8 (2nd GDT entry) with access to the whole 4GB range (base=0,
limit=4GB, 32-bit code)
DS, ES, SS: set to 16 (3rd GDT entry) with access to the whole 4GB range
(base=0, limit=4GB, 32-bit data)
ESP: set to the top of 640KB (ESP=000A0000h)
>From this setup, can I just jump to the beginning of my eCos build?
I notice that the romboot.S in (ecos/packages/hal/i386/pc/current/src) sets up
some specific selectors. Are these mandatory for eCos?
What state should the processor be in upon entry to eCos?
Have I missed the point entirely?
Many thanks.
Martin.
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