dpotop
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BCM 2836 and the RPi 2 ?

Tue Feb 03, 2015 7:55 am

Hello guys,

I think you are all excited by the new Raspberry Pi 2.
However, with new hardware comes the need for new documentation.
Do you happen to know where the peripheral guide of the
new BCM 2836 can be found ?

It may be quite similar to the BCM 2835, but I'd say that at least the
interrupt controller should be different...

Regards,
Dumitru
dpotop

dwelch67
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Re: BCM 2836 and the RPi 2 ?

Tue Feb 03, 2015 10:11 pm

Good point. If they want to advertise as being open or the most open or whatever we need docs for the chip and schematics for the board would be nice too seems like they have become more closed source on that front.

Been struggling to decide to buy one of these things in the us at the high cost of shipping, etc or wait until supply and availability increases, but without docs I have no interest. Easy decision now.

David

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Re: BCM 2836 and the RPi 2 ?

Wed Feb 04, 2015 9:59 am

As far as I know, its the same. The videocore and all the peripherals were retained as it (the RTL didn't change), all that was done was shift the layout over, remove the Arm11 and stick in the quad core A7, add some L2 cache for the ARM (and some minor other tweaks)

The peripheral base address has changed - that can be recovered programatically, but otherwise all should be the same.
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vsiles
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Re: BCM 2836 and the RPi 2 ?

Wed Feb 04, 2015 10:05 am

jamesh wrote: The peripheral base address has changed - that can be recovered programatically, but otherwise all should be the same.
How would you do this ? I didn't know this address could be found programatically.

Best,
V.

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Re: BCM 2836 and the RPi 2 ?

Wed Feb 04, 2015 11:14 pm

vsiles wrote:
jamesh wrote: The peripheral base address has changed - that can be recovered programatically, but otherwise all should be the same.
How would you do this ? I didn't know this address could be found programatically.

Best,
V.
More to the point what is the source of your documentation, how/when do we mere mortals get access to the BCM2836 equivalent of the 'BCM2835-ARM-Peripherals.pdf' documentation.

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Re: BCM 2836 and the RPi 2 ?

Thu Feb 05, 2015 10:12 am

I'm not sure there even is a 2836 document yet. As above, the 2835 one should cover almost everything - the only real difference in the chips is the change to quad-a7's, and the base address change, everything else is the same.

See here for getting the base address

https://github.com/raspberrypi/userland ... 2ca631f0e9
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Re: BCM 2836 and the RPi 2 ?

Thu Feb 05, 2015 11:02 am

jamesh wrote:I'm not sure there even is a 2836 document yet. As above, the 2835 one should cover almost everything - the only real difference in the chips is the change to quad-a7's, and the base address change, everything else is the same.

See here for getting the base address

https://github.com/raspberrypi/userland ... 2ca631f0e9
Is that code backward compatible with PI1 ?

If not, is there a method that works on PI1 and PI2 systems ?

PeterO
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Re: BCM 2836 and the RPi 2 ?

Thu Feb 05, 2015 11:10 am

PeterO wrote:
jamesh wrote:I'm not sure there even is a 2836 document yet. As above, the 2835 one should cover almost everything - the only real difference in the chips is the change to quad-a7's, and the base address change, everything else is the same.

See here for getting the base address

https://github.com/raspberrypi/userland ... 2ca631f0e9
Is that code backward compatible with PI1 ?

If not, is there a method that works on PI1 and PI2 systems ?

PeterO
Should be backwards compatible, might need fairly recent firmware.
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Re: BCM 2836 and the RPi 2 ?

Thu Feb 05, 2015 11:18 am

jamesh wrote: Should be backwards compatible, might need fairly recent firmware.
OK, I just noticed functions that looked like they were releated to the device tree and thus would need a very uptodate kernel to work ?
In the short term I think a solution that works across as wide an age of kernels as possible would be helpful.

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Re: BCM 2836 and the RPi 2 ?

Thu Feb 05, 2015 11:40 am

jamesh wrote:I'm not sure there even is a 2836 document yet. As above, the 2835 one should cover almost everything - the only real difference in the chips is the change to quad-a7's, and the base address change, everything else is the same.

See here for getting the base address

https://github.com/raspberrypi/userland ... 2ca631f0e9
Hi James, thanks for the reply, sorry if I came off as a bit abrasive in my last post...

urm, as my interests mainly lie in 'bare-metal' programming (and my development work is done in a
debian VM with a cross compiler and a serial link upload gizmo) this 'device tree' stuff isn't going to
work for me so like the rest of us 'bare-metal' nerds I am going to have to use a #define for the
base address and re-factor all my code to use it.

other impacts:-
* obviously makefiles are going to need tweaking: -march, -mtune, -mcpu etc...
* link scripts: to utilize the extra ram etc...
* startup code: stack setup, fpu options, mmu, caching etc...
* presumably we will need to add more memory barriers to ensure cache consistency between cpu's...
* ahhhhh blisss...

the BIG thing to take away from all this is that we are looking at a separate build for RPi1x and RPi2x projects.

Regards
Bill

Backwards compatible... Not so much...

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Re: BCM 2836 and the RPi 2 ?

Thu Feb 05, 2015 12:40 pm

PlutoniumBob wrote:
jamesh wrote:I'm not sure there even is a 2836 document yet. As above, the 2835 one should cover almost everything - the only real difference in the chips is the change to quad-a7's, and the base address change, everything else is the same.

See here for getting the base address

https://github.com/raspberrypi/userland ... 2ca631f0e9
Hi James, thanks for the reply, sorry if I came off as a bit abrasive in my last post...

urm, as my interests mainly lie in 'bare-metal' programming (and my development work is done in a
debian VM with a cross compiler and a serial link upload gizmo) this 'device tree' stuff isn't going to
work for me so like the rest of us 'bare-metal' nerds I am going to have to use a #define for the
base address and re-factor all my code to use it.

other impacts:-
* obviously makefiles are going to need tweaking: -march, -mtune, -mcpu etc...
* link scripts: to utilize the extra ram etc...
* startup code: stack setup, fpu options, mmu, caching etc...
* presumably we will need to add more memory barriers to ensure cache consistency between cpu's...
* ahhhhh blisss...

the BIG thing to take away from all this is that we are looking at a separate build for RPi1x and RPi2x projects.

Regards
Bill

Backwards compatible... Not so much...
Bare metal - your choice! I'd expect you to need different builds for Pi2 under these circumstances. Just a makefile define though.

Backwards compatible for the huge majority of people!
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Re: BCM 2836 and the RPi 2 ?

Thu Feb 05, 2015 1:24 pm

jamesh wrote:
PlutoniumBob wrote:
jamesh wrote:I'm not sure there even is a 2836 document yet. As above, the 2835 one should cover almost everything - the only real difference in the chips is the change to quad-a7's, and the base address change, everything else is the same.

See here for getting the base address

https://github.com/raspberrypi/userland ... 2ca631f0e9
Hi James, thanks for the reply, sorry if I came off as a bit abrasive in my last post...

urm, as my interests mainly lie in 'bare-metal' programming (and my development work is done in a
debian VM with a cross compiler and a serial link upload gizmo) this 'device tree' stuff isn't going to
work for me so like the rest of us 'bare-metal' nerds I am going to have to use a #define for the
base address and re-factor all my code to use it.

other impacts:-
* obviously makefiles are going to need tweaking: -march, -mtune, -mcpu etc...
* link scripts: to utilize the extra ram etc...
* startup code: stack setup, fpu options, mmu, caching etc...
* presumably we will need to add more memory barriers to ensure cache consistency between cpu's...
* ahhhhh blisss...

the BIG thing to take away from all this is that we are looking at a separate build for RPi1x and RPi2x projects.

Regards
Bill

Backwards compatible... Not so much...
Bare metal - your choice! I'd expect you to need different builds for Pi2 under these circumstances. Just a makefile define though.

Backwards compatible for the huge majority of people!
urm... this is a 'bare-metal' forum though...
so I guess I am not entirely alone...

dpotop
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Re: BCM 2836 and the RPi 2 ?

Thu Feb 05, 2015 1:54 pm

PlutoniumBob wrote:
jamesh wrote: ...
Bare metal - your choice! ...
urm... this is a 'bare-metal' forum though...
so I guess I am not entirely alone...
No, you're not alone.

To add my thoughts about this:
I want to use the RPis for education in order to teach real-time
systems, and I **do** need bare metal programming to port a
nice real-time OS (not linux, not freertos, but another called POK)
and maybe also to encourage students into understanding the
innards of such an OS.

I chose the RPi because it was education-oriented and
open. If it becomes closed and oriented towards efficient use
(run Linux/Windows, forget about the HW), then it interests me
no more. I'd rather buy Parallela boards with Zynq SoCs, which
have a real Ethernet connection, some industrial relevance,
and allow me to play with HW synthesis, too.

I'll wait for a few days, finish my OS port anyways, and then I'll
make my decision depending on the available information.

Cheers,
Dumitru
dpotop

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Re: BCM 2836 and the RPi 2 ?

Thu Feb 05, 2015 2:44 pm

Why do people think i'ts becoming more closed? That has never been said. In fact, there was a specific statement saying the Foundation would try and make it more open.

Note that the huge majority of Pi's run Linux, it's perfectly fine for education in that form, and that is where the education teams puts it's priorities. Scratch, Python etc are perfectly fine for education of children in the basics of computing. You can even write assembler in Linux if you are so inclined. In fact it necessary when you want to write NEON code effectively.
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dwelch67
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Re: BCM 2836 and the RPi 2 ?

Thu Feb 05, 2015 3:00 pm

This is a bare metal forum, to do bare metal on this platform requires two things, 1) schematics 2) documentation for the parts not just pinouts but also programming documentation.


Eben says things like this:

Yes. VideoCore IV 3d is the only publicly documented 3d graphics core for ARM-based SoCs, and we want to make Raspberry Pi more open over time, not less.

But the schematics have become closed over time and the need for the documentation for the main processor is obvious, and instead of giving us a release date or even what quarter it is targetted for we get brushed off.

Now we are not the largest user of this product no but this product claims to be used for education and IMO one of the main things being lost in the programmer world is bare metal and low level programmers, we have myriads of people programming in more and more languages but fewer and fewer people able to actually build the compilers because fewer and fewer can program assembly or machine code. Bare metal knowledge is required to make operating systems or at least the last mile of an operating system the glue that takes it from theory to reality. That requires bare metal experience. The RPi being not brickable, peripherals that compared to other platforms are very easy to program, etc and the cost and availability make it a very very attractive platform for this form of education. You get the thing in some kids hands so they can learn python or sketch or whatever, and then they find out that when they want to get serious about programming they can learn C, linux operating system stuff then when ready for the ultimate challenge, bare metal. (well verilog/vhdl or other rtl is even more ultimate but this is not the platform for that).

Broadcom blew us away before, well before the RPi was successful, when it was probably going to be just another OLPC, Broadcom ACTUALLY released some documentation about a part publicly without an NDA, limited, but still amazing. It has been a downhill struggle since. I fully believe if that Herman had not done his work that the GPU would still be a secret and Eben wouldnt be able to use marketing speak like that. I firmly believe that had the RPi not become successful there wouldnt have been that motiviation, I also knew immediately when it because a hit that the secrets would be revealed to some extent.

This platform continues to be Broadcoms opportunity to shine and break away from the rest, the moment is or was there, keep it going esp if they want to use it for marketing reasons. Look at what it did for apple A company constantly on the edge of complete failure. Ipod comes out ONLY for mac users, windows hackers figure it out,a ll of the sudden they suport windows to avoid losing control, it becomes the turning point for the company. They switch to intel processors, the hackers figure out how to dual boot and run windows, instantly they start advertising it is a windows computer too. If it wasnt for those bare metal programmers that did that there wouldnt be an Apple today IMO, now they had to partially hack their way in just like Herman, but just like apple Broadcom now uses what the hackers exposed as a marketing angle.

This is really the turning point for me with the RPi, no docs and I move on to some other platform with docs, it is that simple, eventually the old RPi chips will become obsolete as will my interest in using them.

David

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Re: BCM 2836 and the RPi 2 ?

Thu Feb 05, 2015 3:55 pm

I'd agree, the Pi isn't great for baremetal. But then, it was never intended for it, so it's to be expected. It's still one of the most open ARM platforms though, but what Broadcom release is up to Broadcom. Eben does his best but it's really down to Brcm.

So, given that the 2835 docs are good enough for the 2836, what's the actual problem? Lack of schematics? Lack of GPU details? Neither of those have changed between P1 and P2. So why leave the platform now, just as it's performance catches up with every single competitor?
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Re: BCM 2836 and the RPi 2 ?

Thu Feb 05, 2015 4:23 pm

While more docs and openness would be most welcome, I agree with jamessh here.

The Raspberry Pi is an excellent educational platform for programming and introductory interfacing, mainly due to the excellent educational material produced by the foundation (regardless of A/A+/B/B+/2B)

For teaching about bare metal, I'd start with a simpler board, and work my way up, there is no way I'd expect students new to bare metal to be able to program such complex GPU's and VPU's even if the documentation was available.
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Re: BCM 2836 and the RPi 2 ?

Thu Feb 05, 2015 4:37 pm

As an interesting point, I worked on the Videocore GPU for 6 years whilst at Brcm. In that time I did about one day of assembler/baremetal. The rest was C. In fact, as a softie who's been mainly involved in embedded code for about 30 years, not much of it was assembler.(Note, I do have quite a bit of assembler experience but its ancient - 6502, 8051)

But right now, I'm learning ARM assembly and NEON, for fun. Which I will be using under Linux...

So one does wonder exactly how important (for the majority) baremetal and assembly is in teaching, certainly in the initial stages.
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Re: BCM 2836 and the RPi 2 ?

Thu Feb 05, 2015 5:09 pm

When I was doing some hiring for an engineering firm I worked for (and later consulted for) I was very disappointed at the number of applicants who could not properly solve simple pointer oriented problems. Thus, I became convinced that bare metal knowledge was necessary - at least for embedded use.

My favourite microcontroller for hard real time embedded use, and teaching of it, is the Parallax propeller. Eight simple 32 bit RISC cores with 2KB (512 longs) of private memory sharing a 32KB "hub" memory. It is amazing what can be accomplished in 496 longs! (16 are used for I/O and control registers). Very little in the way of peripherals - just two timers per core, and a simple video engine per core for PAL/NTSC or VGA (that can used in many interesting ways). No interrupts! That was an initial mental stumbling block, but it was a deliberate design decision on Chip's part to enforce determinism. Once I got used to it, it worked very well.

A more conventional inexpensive architecture to teach assembly with that I like are the AVR's - I have tubes full of ATMega8's for projects. I like it because of the simple, clean assembly syntax, and not too many too complex peripheral blocks.

To make a long story short... that's why I concentrate on education oriented products. We need more people in the future who can program to the bare metal, and can understand architecture well enough to write good optimizing compilers.

Which is also why I like the PI's emphasis on experimenting with electronics using GPIO's, and the educational material the RPF puts out.
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Re: BCM 2836 and the RPi 2 ?

Thu Feb 05, 2015 6:22 pm

I also agree with dwelch67.
Batteries not included, Some assembly required.

tufty
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Re: BCM 2836 and the RPi 2 ?

Thu Feb 05, 2015 8:13 pm

jamesh wrote:It's still one of the most open ARM platforms though
Ummmmmm - no. No it's not.

The Pi has documentation for the ARM core (thanks to ARM themselves), and the buggy document giving details on some of the peripherals. As for the rest - there's bugger all on the GPU beyond "how to make it do things from ARM-side as long as you want your API to look like OpenGL", the USB IP block is "opaque" to say the least, there's no documentation on the SD card, etc.

Yes, there is the Linux kernel code to fall back on. The dw_otg stuff is buggy as hell, classic "designware example code", it's protoduction quality. I'm not actually aware of *anyone* on *any* platform incorporating the designware USB IP managing to implement OTG mode, for example.

I (and all of us here) are painfully aware that Broadcom can only legally release certain information, and for "souper sekrit eye pee" reasons must keep certain other bits of information "eyes only". It's not Broadcom's fault that Designware won't let us know how to program their IP block. But, even knowing all that, you cannot say what you say above.

You want open? TI's OMAP processors, for example. Full specs and programming manuals available for core & ARM-produced IP blocks, as you would expect, but also the GPU, DSP, etc etc. All without having to try and work out the meaning of the *very opaque* Linux kernel code. If you want to go system level, you could look at Olimex's stuff. Hell, they've managed to get programming documentation out of two *CHINESE* fabs, and their boards come fully open source, down to the engineering drawings. Wanna make your own? Go for it, kid.

In general, there's far more documentation out there for other contemporary SoCs than there is for the 2835/6; ironically it may well be largely down to the success of the Pi, and particularly the documentation Broadcom have grudgingly given out, that this is the case. Which leaves the Pi behind the curve not only in performance terms, but in programmability and openness terms as well. And that sucks.
So, given that the 2835 docs are good enough for the 2836, what's the actual problem? Lack of schematics? Lack of GPU details? Neither of those have changed between P1 and P2. So why leave the platform now, just as it's performance catches up with every single competitor?
The only given is that the 2385 docs aren't good enough for the 2385.

In terms of performance and equipment, the Pi is still behind the curve. Arguably only by 2-3 years now, rather than the 10 when it was released, but it's missing a lot of stuff that's crucial to be taken seriously compared to the current crop of low-cost ARM boards out there. USB3, USB OTG, gigabit (or just "not USB") ethernet, SATA, direct LVDS, the list is long and tedious.

That all sounds grumpy.

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Re: BCM 2836 and the RPi 2 ?

Thu Feb 05, 2015 9:09 pm

Would that be all the other boards that have sold 4.5M, or sold 150k in two days with 1M on backorder.

Clearly those features are not quite as 'required' as you might think.

Anyway, I having nothing further to say on this one, it is what it is. Hopefully in the future, more details will be released, but that's nothing to do with me, (as it does exactly what I need) - that's between the Foundation and Broadcom, and dependent on Eben thinking it's a good idea. Of course, the last time he spent a lot of time and effort getting stuff released he got slated because it wasn't enough, so I guess it's not exactly at the top of his list.
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dwelch67
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Re: BCM 2836 and the RPi 2 ?

Thu Feb 05, 2015 10:31 pm

IMO the ONLY reason that RPi succeeded where OLPC failed is that with the RPi you/they new and catered to the thousands/millions of non-kids that wanted to play with and hack on it. Where OLPC there was a noticeable dollar penalty for that, so no hobbiest grown ups or otherwise folks that would create content for the device were there, no content no buzz no success. Ask a hobbyist if they know what OLPC is, as a non computer person if they know what a Raspberry Pi is, you get the picture.

If you take your numbers of boards and examine just how many are actually being used for the supposedly target audience you will find the product is a failure. Again we are a small group, but we are the non-children that push this product over some alternative that has other goals (chip sales) and provide the information for all users of the product not just the marketing target. The RPi cannot and will not survive if the developers are closed off.

Your product will die if only Broadcom paid developers are writing all the software and only children are using it (your numbers will be to small to sustain the production line, you would not meed the price point). Please remember that. Without an army of non-children buying and playing with this board, a low end laptop would be significantly cheaper than an RPi. A significant number of folks will return to arduinos and nucleos and beaglebones if each developer group is ignored...Also remember there is no linux, no gcc, no python, no software without some very small group of people that write bootloaders, drivers, and compilers.

I believe this actually is a good bare metal platform, a few more pennies per board would make it even better and a few painless docs even better still. Not brickable so far as we know, peripherals are very easy to program once properly documented, trivial to boot and try new programs. It has all the factors to be superior to the other hundreds of boards I have used, except...good/properly documented peripherals...

We get that your hands are tied as are those above you, choose different words next time than those that got us all fired up.

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Re: BCM 2836 and the RPi 2 ?

Thu Feb 05, 2015 11:23 pm

PlutoniumBob wrote:urm, as my interests mainly lie in 'bare-metal' programming (and my development work is done in a
debian VM with a cross compiler and a serial link upload gizmo) this 'device tree' stuff isn't going to
work for me so like the rest of us 'bare-metal' nerds I am going to have to use a #define for the
base address and re-factor all my code to use it.

you could still use device-tree in the baremetal code, if start.elf is acting as the loader, or your serial part can forward the DTB

just need to look-up the DTB specs, walk the tree, and find the node in question from the baremetal code

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Re: BCM 2836 and the RPi 2 ?

Fri Feb 06, 2015 3:02 am

cleverca22 wrote:
PlutoniumBob wrote:urm, as my interests mainly lie in 'bare-metal' programming (and my development work is done in a
debian VM with a cross compiler and a serial link upload gizmo) this 'device tree' stuff isn't going to
work for me so like the rest of us 'bare-metal' nerds I am going to have to use a #define for the
base address and re-factor all my code to use it.
you could still use device-tree in the baremetal code, if start.elf is acting as the loader, or your serial part can forward the DTB
just need to look-up the DTB specs, walk the tree, and find the node in question from the baremetal code
Thanks for the input but I still have to patch all MY code/libs to use whatever solution I decide to go with;
and right now a #define or a value picked up from the ld script seems favorite.

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