[RFC] Raspberry PI

[Giovanni]

Hi,

Need info

Is there any interest for a ChibiOS port? does it make sense? anybody willing to help with this one or at least has knowledge with the HW?

It doesn't look simple like a normal port, probably ChibiOS would have to be booted from the SD card instead than flashed like usual. It would be interesting but not not so easy. The real question is, is such an high end processor (compared to MCUs) a legitimate target for something like ChibiOS?

Giovanni

[Jacon]

The real question is, is such an high end processor (compared to MCUs) a legitimate target for something like ChibiOS?
Giovanni

In my opinion - no!
That Broadcom-made chip has ordinary ARM CPU & peripherals, with all documentation available (now, or in the future,
according to Foundation people) and advanced GPU part, which would have Linux only driver, and lack of any
more fundamental info
Quote from available CPU manual:

1.1 Overview
BCM2835 contains the following peripherals which may safely be accessed by the ARM:
• Timers
• Interrupt controller
• GPIO
• USB
• PCM / I2S
• DMA controller
• I2C master
• I2C / SPI slave
• SPI0, SPI1, SPI2
• PWM
• UART0, UART1
The purpose of this datasheet is to provide documentation for these peripherals in sufficient
detail to allow a developer to port an operating system to BCM2835.
There are a number of peripherals which are intended to be controlled by the GPU. These are
omitted from this datasheet. Accessing these peripherals from the ARM is not recommended.

All that a.m. GPU info is classified by Broadcom

So Linux (or its RT incarnations) is the natural habitat for that hardware...

[mabl]

Seconded.

I feel like the Pi is just too complex. If people want to start learning ChibiOS, they better do it on "smaller" devices such as the STM32.

[Badger]

These points are all true, but it might actually serve a useful purpose in terms of what the Raspberry Pi is actually designed for; education. Running an operating system which a user could work their way through and understand throughout would be pretty cool. Obviously that's no different to what someone could do with one of the many dev boards that chibios supports, but you don't see people queueing to buy those! so maybe from a publicity / novelty point of view it would have use.

[utzig]

I personally would not run ChibiOS no such target. I pretty much like running Linux when the hardware is powerful enough. The most positive thing of a port to the Raspeberry PI IMO would be serving to open the way to future ports to other more powerful HW like ARM9s/11s/CA-8s/etc.

Fabio Utzig

[Giovanni]

Good points, technically speaking such a SOC is not the best target for ChibiOS but there are other things to consider:

1) I am in touch with a person who offered to donate the required HW and has knowledge to make this port easier. Before accepting anything I have to verify feasibility.
2) The ARM11 should not be that different from the ARM9 which is already supported (I have to verify this point).
3) I think the R-PI firmware does all required initializations, a complex HAL driver (think STM32) would not be required. The initial support could be just PAL and Serial drivers. SPI, SDIO, Ethernet, USB, etc could follow if the project is successful.
4) It could be a platform where experimenting with that idea of a standalone ChibiOS loading its own applications. The SD card would contain the kernel image, the kernel would then bootload the application from the same SD card.
5) The R-PI is extremely popular linking ChibiOS to it could give impulse to the project. There were people asking for ChibiOS on the R-PI forum so some kind of demand seems to exist.

The undocumented GPU thing is bothering me, would this mean we would not have access to a frame buffer?

Giovanni

[Jacon]

The undocumented GPU thing is bothering me, would this mean we would not have access to a frame buffer?

Definitely - not!
High level API functions only

[mabl]

I just cannot understand why some companies have so much trouble documenting their hardware openly....

Anyway, I think there is also a RISC OS Port in the works, and it seems they also have trouble:
http://www.riscosopen.org/forum/forums/ ... osts-10565

Probably one has to look at the Linux driver and see how they do it.

[Jacon]

Probably one has to look at the Linux driver and see how they do it.

You would see high level functions internal structure only...
All of low level GPU firmware is in SOC ROM

[mabl]

Probably one has to look at the Linux driver and see how they do it.

You would see high level functions internal structure only...
All of low level GPU firmware is in SOC ROM

True, but we could also load that blob. And I was also looking for USB which is also not freely documented according to the link.

Probably it would be a good idea to ask the RiscOS guys where they have/had troubles.