[ECOS] Re: RAM vs. ROMRAM question

Nick Garnett nickg@ecoscentric.com
Tue Oct 31 17:32:00 GMT 2006

Grant Edwards <grante@visi.com> writes:

> >>>What is the exact complaint you are getting?
> >> 
> >> That being a ROM monitor is a conflict with RAM startup but not
> >> with ROMRAM startup.
> >
> > ecos.ecc:
> >
> > cdl_option CYGSEM_HAL_ROM_MONITOR {
> >      # Flavor: bool
> >      # No user value, uncomment the following line to provide one.
> >      # user_value 0
> >      # value_source default
> >      # Default value: 0
> >      # Requires:  CYG_HAL_STARTUP == "ROM" || CYG_HAL_STARTUP == "ROMRAM"
> Exactly.  
> It's been stated that it doesn't make sense for
> CYGSEM_HAL_ROM_MONITOR to be set for RAM startup because
> RedBoot would be loading apps into the RAM where RedBoot itself
> is running.  
> ROMRAM RedBoot runs in the exact same memory locations as RAM
> RedBoot, so why doesn't that reasoning apply to ROMRAM startup?

No. ROMRAM RedBoot loads to low RAM, usually the bottom 128K. RAM
applications and RAM RedBoot would load above 128K. ROM RedBoot would
keep its code in ROM but put its data below 128K, and the rest of
memory up to 128K would be unused. JTAG RedBoot would load in the
bottom 128K just like ROMRAM.

Under normal circumstances a RAM RedBoot is only needed when RedBoot
is normally run out of ROM, and then only to enable the ROM image to
be reprogrammed. So, it is not necessary for a RAM RedBoot to be
capable of loading and debugging an application. Hence

Nick Garnett                                     eCos Kernel Architect
http://www.ecoscentric.com                The eCos and RedBoot experts

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