[ECOS] MIPS32 4Kc - Interrupt enable and base address for exceptions

[ECOS] MIPS32 4Kc - Interrupt enable and base address for exceptions

[Elad Yosef]

Hi,
MIPS32 4Kc has 2 base addresses for exceptions
bootstrap - 0xBFC00000
normal -     0x80000000

The selection of the base address is by BEV bit in the status register.

In the Boot stage it makes sense that the BEV will select the bootstrap.
but when the application is running from RAM i want it to use the
normal base (mapped to my RAM)

My RedBoot works fine, downloads the application by tftp to RAM and jumps to it.

My application init code is also running well, until the exit from
"cyg_user_start".

The eCos default - Is that point the scheduler goes to action and
interrupts are enabled.

At that point I see that my CPU still using the bootstrap base for
exceptions/interrupt.
which leads to unexpected results.

My question is- Is there some configuration option i need to select in
order to use the "normal" base?

In case there isn't such, At which point on the code should I set the
BEV in the status register?

Thanks

Elad

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Re: [ECOS] MIPS32 4Kc - Interrupt enable and base address for exceptions

[Stefan Sommerfeld]

Hi Elad,

> MIPS32 4Kc has 2 base addresses for exceptions
> bootstrap - 0xBFC00000
> normal -     0x80000000
> 
> The selection of the base address is by BEV bit in the status register.
> 
> In the Boot stage it makes sense that the BEV will select the bootstrap.
> but when the application is running from RAM i want it to use the
> normal base (mapped to my RAM)
> 
> My RedBoot works fine, downloads the application by tftp to RAM and jumps to it.
> 
> My application init code is also running well, until the exit from
> "cyg_user_start".
> 
> The eCos default - Is that point the scheduler goes to action and
> interrupts are enabled.
> 
> At that point I see that my CPU still using the bootstrap base for
> exceptions/interrupt.
> which leads to unexpected results.
> 
> My question is- Is there some configuration option i need to select in
> order to use the "normal" base?
> 
> In case there isn't such, At which point on the code should I set the
> BEV in the status register?
> 

I use normal vectors too. Here are the things you need to do:

- you need the code for the vectors at address 0, so copy the current code (from
your eCos to address 0x00000000)
- store DCache or invalidate it (depending on cached or uncached memory access)
- set BEV to normal base

You must make sure you don't use the first 1KB from memory, so you wont alter
you vectors code.

But think of what you're doing. This will not gain to much, because you can set
all interrupts to memory base routines without BEV. eCos will quickly jump to
the routine from the interrupt vectors table. You can also make your FLASH cachable.

Bye...

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Re: [ECOS] MIPS32 4Kc - Interrupt enable and base address for exceptions

[Elad Yosef]

Thanks
I was sure that the eCos code already clears the BEV in status register.

Once I clear it, it all works great.
I'll just add some code to clear BEV

Thanks again
Elad

On Tue, Jan 18, 2011 at 3:30 PM, Stefan Sommerfeld <sommerfeld@mikrom.de> wrote:
> Hi Elad,
>
>> MIPS32 4Kc has 2 base addresses for exceptions
>> bootstrap - 0xBFC00000
>> normal -     0x80000000
>>
>> The selection of the base address is by BEV bit in the status register.
>>
>> In the Boot stage it makes sense that the BEV will select the bootstrap.
>> but when the application is running from RAM i want it to use the
>> normal base (mapped to my RAM)
>>
>> My RedBoot works fine, downloads the application by tftp to RAM and jumps to it.
>>
>> My application init code is also running well, until the exit from
>> "cyg_user_start".
>>
>> The eCos default - Is that point the scheduler goes to action and
>> interrupts are enabled.
>>
>> At that point I see that my CPU still using the bootstrap base for
>> exceptions/interrupt.
>> which leads to unexpected results.
>>
>> My question is- Is there some configuration option i need to select in
>> order to use the "normal" base?
>>
>> In case there isn't such, At which point on the code should I set the
>> BEV in the status register?
>>
>
> I use normal vectors too. Here are the things you need to do:
>
> - you need the code for the vectors at address 0, so copy the current code (from
> your eCos to address 0x00000000)
> - store DCache or invalidate it (depending on cached or uncached memory access)
> - set BEV to normal base
>
> You must make sure you don't use the first 1KB from memory, so you wont alter
> you vectors code.
>
> But think of what you're doing. This will not gain to much, because you can set
> all interrupts to memory base routines without BEV. eCos will quickly jump to
> the routine from the interrupt vectors table. You can also make your FLASH cachable.
>
> Bye...
>

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