[ECOS] JFFS2 filesystem and eCos code on the same chip?

[Jonathan Larmour]

Gary Thomas wrote:
> On Tue, 2002-10-15 at 07:28, Andrew Lunn wrote:
> 
>>On Tue, Oct 15, 2002 at 03:26:22PM +0200, llandre wrote:
>>
>>>Is it possible to have the JFFS2 file system and eCos binary code on the 
>>>same physical chip?
>>
>>The flash driver API functions copy themselves itself into RAM before
>>doing anything with the flash. Redboot uses this feature.
> 
> 
> Firstly, it's not common to actually be executing from FLASH.  RedBoot
> does this, and an application can do so as well, but the more common
> case is for programs to execute out of RAM.

I'm not sure I'd make that generalisation. XIP is an obvious way to reduce 
costs in final production boards for applications where performance isn't 
critical (assuming it's slower, which it isn't always).

It's not much of an issue in the fairly high end *development* boards us 
guys tend to use I agree :-).

 > That noted, the drivers
> are designed to handle this case anyway by insisting that the access
> routines are in RAM before running them.
> 
> 
>>What i don't know about is if this is thread safe. Does the flash code
>>disable interrupts while its doing dangerous things? You need to check
>>the code, or probably Gary knows.
> 
> This is an interesting observation.  Currently nothing specific is being
> done about interrupts.  It probably should, so I'll think about it.

In fact, it definitely should if e.g. you are running out of Flash! I'll 
raise a bugzilla bug for this unless you want to deal with it imminently - 
it can at least be conditionalized on CYG_HAL_STARTUP_ROM.

It isn't obvious that it should be done all the time though as although 
the case of XIP is pretty glaring, other situations aren't - if it was a 
RAM or ROMRAM program and the app only accesses flash via e.g. JFFS2 then 
it's no big deal.

And indeed Jay mentions watchdogs, and the problem of having ints disabled 
for a long time.

Perhaps we should only do it for CYG_HAL_STARTUP_ROM and the user can 
shoot themselves in the head/foot/wherever if they want.

Jifl
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