RISC-V interrupt vectoring

[Hesham Almatary]

Hi Denis,

It's not clear from your output which instruction is causing the fault.

You can debug this by investigating mcause value after the faulting
instruction, and see what's the value in s0, and whether it's valid or
not.

It's also a good idea to use objdump and/or Spike/Qemu for debugging
(I think either or both have a model of HiFive board, you might want
to check).

Make sure you don't use compressed instructions, for now, there's a
flag you can pass to GCC to do this, you might want to do some
research on it.

On Tue, Jul 4, 2017 at 9:47 PM, Denis Obrezkov <denisobrezkov at gmail.com> wrote:
> 2017-07-03 21:17 GMT+02:00 Joel Sherrill <joel at rtems.org>:
>>
>>
>>
>> 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
>>>
>>> _______________________________________________
>>> devel mailing list
>>> devel at rtems.org
>>> http://lists.rtems.org/mailman/listinfo/devel
>>>
>>>
>> 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
>>
>>
>
> I found out, that I have an exception "Illegal instruction", I get this
> exception after I step in:
> 0x204007c2 in Clock_initialize (major=0, minor=0, pargp=0x0)
>     at
> /home/reprofy/Projects/riscv/rtems/development/rtems/kernel/rtems-riscv/c/src/lib/libbsp/riscv32/hifive1/../../shared/clockdrv_shell.h:182
>
>
> from
> 0x2040ef06 in rtems_io_initialize (major=0, minor=0, argument=0x0)
>     at
> /home/reprofy/Projects/riscv/rtems/development/rtems/kernel/rtems-riscv/c/src/../../cpukit/sapi/src/ioinitialize.c:36
>
> But this is a part of my disas output for 0x204007c2 address:
>    0x204007b8 <+16>:    sw      a2,-44(s0)
>    0x204007bc <+20>:    lui     a5,0x80001
>    0x204007c0 <+24>:    sw      zero,-1576(a5) # 0x800009d8
>    0x204007c4 <+28>:    sw      zero,-20(s0)
>    0x204007c8 <+32>:    lui     a5,0x80001
>    0x204007cc <+36>:    li      a4,1
>    0x204007ce <+38>:    sb      a4,-1580(a5) # 0x800009d4
>
> How is it possible?
>
> --
> Regards, Denis Obrezkov



-- 
Hesham