RISC-V interrupt vectoring

[Joel Sherrill]

On Jul 3, 2017 12:45 PM, "Denis Obrezkov" <denisobrezkov at gmail.com> wrote:

2017-07-03 19:09 GMT+02:00 Joel Sherrill <joel at rtems.org>:

>
>
> On Jul 3, 2017 11:49 AM, "Denis Obrezkov" <denisobrezkov at gmail.com> wrote:
>
> 2017-07-03 7:43 GMT+02:00 Hesham Almatary <heshamelmatary at gmail.com>:
>
>> On Mon, Jul 3, 2017 at 3:36 PM, Denis Obrezkov <denisobrezkov at gmail.com>
>> wrote:
>> > 2017-07-03 4:59 GMT+02:00 Hesham Almatary <heshamelmatary at gmail.com>:
>> >>
>> >> You can have a look at riscv-pk [1] as a RISC-V reference how to
>> >> handle interrupts. RTEMS-wise, you can look at or1k and ARM code and
>> >> how the platform-dependent interrupt handling code is linked to
>> >> platform-independent one.
>> >>
>> >> mcause value can be used as an index to a software vector table that
>> you
>> >> set up.
>> >>
>> >> Why do you need software interrupts? GSoC-wise, I thought the plan was
>> >> to develop UART/Console driver (which doesn't need interrupts), and
>> >> use simulated ticker, as a first step. Then it will be easier to
>> >> debug/proceed from there with interrupt handling code.
>> >
>> > I thought, I have to implement an interrupt console driver. Okay, then
>> I am
>> > going to
>> > investigate a simulated ticker.
>> Yeah that can be done in later stages, for optimisation purposes. But
>> I think it's easier to implement it in polling mode first, just to get
>> things working, then you can easily move to interrupt-based
>> implementation. For example, if you've a polling console driver, you
>> can debug using printk, when developing the clock driver. Once you get
>> the clock driver working, you will have a more mature code for
>> interrupt handling, which enables you to very easily implement
>> interrupt-based UART driver.
>> > --
>> > Regards, Denis Obrezkov
>>
>>
>>
>> --
>> Hesham
>>
>
> It seems that vectored interrupts aren't available in FE310 SoC.
> Thus, I will work with mcause register.
> As for now, I want to:
> * add local interrupt handlers
> * add init code for counters initializtion (since we want to set up a
> baudrate)
> * implement a dummy clock driver
>
>
> This is easy and just requires one line in the BSP Makefile.am and an
> include in the .tcfg file to skip tests known to fail. See either the shsim
> or v850sim BSPs based on gdb for examples.
>
> It also lets you have all the tests running so you can add your target to
> RTEMS tester. :)
>
> * implement a polling uart
>
>
> Personally I would do this as soon as possible and get printk working.
> Very helpful and needed to run the tests with simulated clock tick with the
> polled driver.
>
> The counter is only needed for math on the baud rate I would guess.
>
> * figure out how interrupts are handled in RTEMS
> * implement global interrupt handlers
> * implement a clock driver
> * implement an interrupt-mode uart driver.
>
>
>
> --
> Regards, Denis Obrezkov
>
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>
> Ok, I will try to make a uart driver as soon as possible.
I had some issues with dummy_clockdriver, I think there was a mistake,
that an address of clock initialization function was wrong, so, I will
investigate it tomorrow.
Also, I have a problem, as I mentioned earlier, that the minimum example
finished with the error ''INTERNAL_ERROR_THREAD_EXITTED".


That is probably the correct behavior. It is not intended to be executed.
It is just an example of how to strip down a configuration to get a program
running. The Init thread is completely empty as I recall so it would return
and fail like this.

I would move on to hello. Use the existing sim clock driver and the polled
console driver framework until this much all works. See how the two BSPs I
mentioned earlier do things. That will minimize the amount of code you have
to write until you can focus on the interrupts.

Also.. hello world is the first step. Usually adding a delay/sleep call to
that or using ticker/sp01 is how to debug a clock driver and interrupt
driven console driver.




-- 
Regards, Denis Obrezkov
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