RTEMS on embedded CPUs(RISCV)

[Sebastian Huber]

On 05/06/2019 12:20, Sachin Ghadi wrote:
> Thanks Sebastian,
>
> On Wed, Jun 5, 2019 at 10:41 AM Sebastian Huber
> <sebastian.huber at embedded-brains.de> wrote:
>> Hello Sachin,
>>
>> On 05/06/2019 06:15, sachin.ghadi at sifive.com wrote:
>>> Hi RTEMS dev team,
>>>
>>> I don’t know if I should send this query to users list or developer list.
>>>
>>> I am working on the getting RTEMS BSP ported on the one of RISC-V
>>> based SoC.
>>>
>>> Current RTEMS has support only for Spike simulator.
>>>
>> we have also support for Qemu. At least at some point in time it worked
>> with a non-upstream Qemu. I am not sure how far the upstreaming of the
>> Qemu support progressed in the last months.
>>
>>> It looks like RTEMS does not fit very well on the systems having less RAM.
>>>
>>> We have 64K of RAM on our standard FPGA development kit for our E
>>> series embedded cores.
>>>
>> 64KiB for code and data is a challenge for RTEMS. You have to tinker
>> with the configuration and reduce the feature set to get into this range.
>>
> Yes 64K is challenge,for both data and code.
> I can use external xip flash for code and but I need to change linker
> script and start up code to load data section from flash to RAM.
> I see RTEMs uses some initialized global variables.

We have to adjust

bsps/riscv/riscv/start/linkcmds.in

so that a ROM can be optionally used for text and read-only data.

>
>
>>> All of the RTEMS test does not fit within this given RAM and linker
>>> throws error.
>>>
>>> Regarding this I have few questions
>>>
>>>   1. Does RTEMS accept support for new core with limited tests passing?
>>>      Or one need full test suit passing to qualify complete test?
>>>
>> What do you mean with "new core"? I think we already support the
>> practically relevant ISA combinations:
> I guess 'core' is wrong word I used..I mean new BSP for our RISCV
> based hardware development kit(Arty100). Core is rv32imac.

The current BSP uses a device tree for initialization. Do you want to 
use this also for this tiny system? If not, then we have to find a way 
to initialize everything with a static configuration.

-- 
Sebastian Huber, embedded brains GmbH

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