millerthegorilla
Posts: 10
Joined: Tue Feb 17, 2015 6:16 pm

BCM2836 datasheet

Wed Feb 18, 2015 11:50 am

Hi, I am trying to locate the datasheet for the BCM2836 in order to understand some of the kernel config options. Does anyone know if the datasheet is available, and if not, who I can ask?

Presumably the Pi manufacturers have the ability as sales contacts of Broadcom to make a request to Broadcom for the datasheet?

ghans
Posts: 7874
Joined: Mon Dec 12, 2011 8:30 pm
Location: Germany

Re: BCM2836 datasheet

Wed Feb 18, 2015 11:56 am

Thre is no dedicated datasheet for the BCM2836 (yet ?!), you have use the one for the BCM2835 .

This thread is full of links to stuff you might find interesting and useful :

http://www.raspberrypi.org/forums/viewt ... 72&t=72260

ghans
• Don't like the board ? Missing features ? Change to the prosilver theme ! You can find it in your settings.
• Don't like to search the forum BEFORE posting 'cos it's useless ? Try googling : yoursearchtermshere site:raspberrypi.org

jamesh
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 23879
Joined: Sat Jul 30, 2011 7:41 pm

Re: BCM2836 datasheet

Wed Feb 18, 2015 12:00 pm

This is about the 5th time this exact questions has been asked on here. Is there a problem that searches are not finding the information?
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
Contrary to popular belief, humorous signatures are allowed. Here's an example...
“I think it’s wrong that only one company makes the game Monopoly.” – Steven Wright

ghans
Posts: 7874
Joined: Mon Dec 12, 2011 8:30 pm
Location: Germany

Re: BCM2836 datasheet

Wed Feb 18, 2015 12:03 pm

Braodcom releasing datasheets is kind of a big deal ... AFAIK Eben himself wrote the blog post about it in 2012 (2013 ?) so an update in the same vein
for the Pi2 would certainly make googling easier ..

ghans
• Don't like the board ? Missing features ? Change to the prosilver theme ! You can find it in your settings.
• Don't like to search the forum BEFORE posting 'cos it's useless ? Try googling : yoursearchtermshere site:raspberrypi.org

millerthegorilla
Posts: 10
Joined: Tue Feb 17, 2015 6:16 pm

Re: BCM2836 datasheet

Wed Feb 18, 2015 12:52 pm

Thanks, I did see the other links to datasheet enquiries about the BCM2836 but they are not exclusively about the datasheet. The other thing is that I was wondering if there had been any advance in obtaining a datasheet. I am not certain that one would go about manufacturing a chip without being able to provide specifications for such a chip - as I understand it, it is no real big deal to provide a datasheet, its just that Broadcom are not always forthcoming with information.

The difference between the Broadcom 2835 and the 2836 is undoubtedly large enough to warrant access to a datasheet.
I imagine that Microsoft, in designing a raspberry pi windows 10 release have made full use of the datasheet that they will have obtained from Broadcom; knowing the exact specifications will provide access to performance tuning that is necessary to obtain a running windows kernel on a non generic device. So there must exist a datasheet.

ghans
Posts: 7874
Joined: Mon Dec 12, 2011 8:30 pm
Location: Germany

Re: BCM2836 datasheet

Wed Feb 18, 2015 1:00 pm

If you are serious about this you propably have to speak personally with Eben himself , E-Mails won't cut it.

I'm going to boldly predict that he himself has first to be greenlighted by Broadcoms legal department before telling you anything.

ghans
• Don't like the board ? Missing features ? Change to the prosilver theme ! You can find it in your settings.
• Don't like to search the forum BEFORE posting 'cos it's useless ? Try googling : yoursearchtermshere site:raspberrypi.org

jamesh
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 23879
Joined: Sat Jul 30, 2011 7:41 pm

Re: BCM2836 datasheet

Wed Feb 18, 2015 2:29 pm

millerthegorilla wrote:Thanks, I did see the other links to datasheet enquiries about the BCM2836 but they are not exclusively about the datasheet. The other thing is that I was wondering if there had been any advance in obtaining a datasheet. I am not certain that one would go about manufacturing a chip without being able to provide specifications for such a chip - as I understand it, it is no real big deal to provide a datasheet, its just that Broadcom are not always forthcoming with information.

The difference between the Broadcom 2835 and the 2836 is undoubtedly large enough to warrant access to a datasheet.
I imagine that Microsoft, in designing a raspberry pi windows 10 release have made full use of the datasheet that they will have obtained from Broadcom; knowing the exact specifications will provide access to performance tuning that is necessary to obtain a running windows kernel on a non generic device. So there must exist a datasheet.
The 2835 and 2836 are extremely similar. In fact the GPU side is identical (even down to the RTL). As are all the peripherals, so you can indeed use the 2835 datasheet, with simply a change in peripheral address and something to do with userland DMA I cannot quite remember right now (caching?).

The only worthwhile difference is that the Armv9 has been replaced with 4 cortex A7's, and there is a different cache arrangement.

So in effect, add that last line to the 2835 datasheet, change base address and add a paragraph on DMA and the new cache, and you have a 2836 datasheet.

It really is that simple.

What isn't simple is getting Broadcom to release this stuff. They have a legal department that measures time in eons. Not only that, but I suspect that a 2836 datasheet doesn't yet exist.
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
Contrary to popular belief, humorous signatures are allowed. Here's an example...
“I think it’s wrong that only one company makes the game Monopoly.” – Steven Wright

mimi123
Posts: 583
Joined: Thu Aug 22, 2013 3:32 pm

Re: BCM2836 datasheet

Wed Feb 18, 2015 3:01 pm

jamesh wrote:
millerthegorilla wrote:Thanks, I did see the other links to datasheet enquiries about the BCM2836 but they are not exclusively about the datasheet. The other thing is that I was wondering if there had been any advance in obtaining a datasheet. I am not certain that one would go about manufacturing a chip without being able to provide specifications for such a chip - as I understand it, it is no real big deal to provide a datasheet, its just that Broadcom are not always forthcoming with information.

The difference between the Broadcom 2835 and the 2836 is undoubtedly large enough to warrant access to a datasheet.
I imagine that Microsoft, in designing a raspberry pi windows 10 release have made full use of the datasheet that they will have obtained from Broadcom; knowing the exact specifications will provide access to performance tuning that is necessary to obtain a running windows kernel on a non generic device. So there must exist a datasheet.
The 2835 and 2836 are extremely similar. In fact the GPU side is identical (even down to the RTL). As are all the peripherals, so you can indeed use the 2835 datasheet, with simply a change in peripheral address and something to do with userland DMA I cannot quite remember right now (caching?).

The only worthwhile difference is that the Armv9 has been replaced with 4 cortex A7's, and there is a different cache arrangement.

So in effect, add that last line to the 2835 datasheet, change base address and add a paragraph on DMA and the new cache, and you have a 2836 datasheet.

It really is that simple.

What isn't simple is getting Broadcom to release this stuff. They have a legal department that measures time in eons. Not only that, but I suspect that a 2836 datasheet doesn't yet exist.
If the Pi1 had an ARMv9...
Aside from that, it is possible to detect the HWrev without using a register with ATAGs.

jamesh
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 23879
Joined: Sat Jul 30, 2011 7:41 pm

Re: BCM2836 datasheet

Wed Feb 18, 2015 4:51 pm

mimi123 wrote:
jamesh wrote:
millerthegorilla wrote:Thanks, I did see the other links to datasheet enquiries about the BCM2836 but they are not exclusively about the datasheet. The other thing is that I was wondering if there had been any advance in obtaining a datasheet. I am not certain that one would go about manufacturing a chip without being able to provide specifications for such a chip - as I understand it, it is no real big deal to provide a datasheet, its just that Broadcom are not always forthcoming with information.

The difference between the Broadcom 2835 and the 2836 is undoubtedly large enough to warrant access to a datasheet.
I imagine that Microsoft, in designing a raspberry pi windows 10 release have made full use of the datasheet that they will have obtained from Broadcom; knowing the exact specifications will provide access to performance tuning that is necessary to obtain a running windows kernel on a non generic device. So there must exist a datasheet.
The 2835 and 2836 are extremely similar. In fact the GPU side is identical (even down to the RTL). As are all the peripherals, so you can indeed use the 2835 datasheet, with simply a change in peripheral address and something to do with userland DMA I cannot quite remember right now (caching?).

The only worthwhile difference is that the Armv9 has been replaced with 4 cortex A7's, and there is a different cache arrangement.

So in effect, add that last line to the 2835 datasheet, change base address and add a paragraph on DMA and the new cache, and you have a 2836 datasheet.

It really is that simple.

What isn't simple is getting Broadcom to release this stuff. They have a legal department that measures time in eons. Not only that, but I suspect that a 2836 datasheet doesn't yet exist.
If the Pi1 had an ARMv9...
Aside from that, it is possible to detect the HWrev without using a register with ATAGs.
Sorry, that should have read Arm11...!
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
Contrary to popular belief, humorous signatures are allowed. Here's an example...
“I think it’s wrong that only one company makes the game Monopoly.” – Steven Wright

amalinda.gamage
Posts: 11
Joined: Tue Jul 09, 2013 3:14 am

Re: BCM2836 datasheet

Mon Apr 20, 2015 1:48 am

BCM2836 and BCM2835 uses two different ARM architectures. So the datasheet will indeed be different. It is absurd that Broadcom is not releasing the datasheet. At least we have to accept that.

As architectures used by BCM2836 and BCM2835 are very different. Indeed they have a lot of similarities but equally, they have a lot of differences. One cannot simply look at the BCM2835 datasheet and design a product for the BCM2836.

For example, one supports the new kernel and the other doesn't. These are big differences tightly integrated to the architecture and one needs to consider these very carefully.

What is this fuss with Broadcom and datasheets? Why are they are so scared to release datasheets. phew.

ShiftPlusOne
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 6031
Joined: Fri Jul 29, 2011 5:36 pm
Location: The unfashionable end of the western spiral arm of the Galaxy

Re: BCM2836 datasheet

Mon Apr 20, 2015 2:39 am

amalinda.gamage wrote:One cannot simply look at the BCM2835 datasheet and design a product for the BCM2836.
Depends on the product, but why would anybody do that? There's a BCM2836 documentation section for a reason. There's also this forum, where any missing information could be requested.

User avatar
rpdom
Posts: 15391
Joined: Sun May 06, 2012 5:17 am
Location: Chelmsford, Essex, UK

Re: BCM2836 datasheet

Mon Apr 20, 2015 2:57 am

amalinda.gamage wrote:BCM2836 and BCM2835 uses two different ARM architectures. So the datasheet will indeed be different.
Not at all. The BCM2835 Peripherals document that everyone is talking about doesn't really cover the ARM CPU at all. There are separate ARM docs for that, which are available.

The rest of the chip hasn't changed much and the most relevant details have been given and documented.

ghans
Posts: 7874
Joined: Mon Dec 12, 2011 8:30 pm
Location: Germany

Re: BCM2836 datasheet

Mon Apr 20, 2015 5:17 am

This is the new peripherials datasheet for the BCM2836 :

https://www.raspberrypi.org/documentati ... rev3.4.pdf


ghans
• Don't like the board ? Missing features ? Change to the prosilver theme ! You can find it in your settings.
• Don't like to search the forum BEFORE posting 'cos it's useless ? Try googling : yoursearchtermshere site:raspberrypi.org

jamesh
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 23879
Joined: Sat Jul 30, 2011 7:41 pm

Re: BCM2836 datasheet

Mon Apr 20, 2015 7:13 am

amalinda.gamage wrote:As architectures used by BCM2836 and BCM2835 are very different. Indeed they have a lot of similarities but equally, they have a lot of differences. One cannot simply look at the BCM2835 datasheet and design a product for the BCM2836.
I suspect for most cases you actually can. However, if you are designing a product at the chip level, then you should be talking to Broadcom directly, since the chip is generally not available to purchase except in large quantities. If you are not going to be selling 100k's of product, then you are better off looking at the compute module.
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
Contrary to popular belief, humorous signatures are allowed. Here's an example...
“I think it’s wrong that only one company makes the game Monopoly.” – Steven Wright

JoGusto
Posts: 15
Joined: Mon May 04, 2015 7:03 pm
Location: San Francisco Bay Area

Re: BCM2836 datasheet

Mon May 18, 2015 7:42 pm

ShiftPlusOne wrote:
amalinda.gamage wrote:One cannot simply look at the BCM2835 datasheet and design a product for the BCM2836.
Depends on the product, but why would anybody do that? There's a BCM2836 documentation section for a reason. There's also this forum, where any missing information could be requested.
SMH.... you are totally missing Amalinda's point. Someone responsible for a kernel should be able to know every aspect of the bare metal behavior in order to do her job. The data sheet is where that comes from.

On the other hand, I do know that releasing complicated stuff without public documentation is pretty common practice. Freescale does it all the time. They design a chip to suit a particular BIG customer, such as BMW or Audi (in the case of something like the MPC5200 PowerPC SOC) and never, ever release documentation for certain pieces of the SoC hardware (eg, the "BestComm" microcoded DMA engine microcode command set). Why do they behave this way? They don't want the support headaches of dealing with the gnats who will try to use this information, potentially, and then have a question when they encounter the inevitable chip hardware bugs that the BIG customer simply worked around.... "it's good enough" but not really good enough for prime time.

Or it may just be a simple fact that revealing too much information publicly about the chip architecture makes it just that much easier for a Far Eastern cloner company to duplicate the chip and make cheap knockoff boxes. Reverse engineering a complex SoC chip is quite tedious using electron microscopy. A detailed functional description is a big help for someone wanting to do that.

I'm sure Broadcom didn't develop the '36 chip for the RPi foundation. They had a commercial customer in mind, one who was upping the ante with a set-top box or a DVR, and needed the extra horsepower that the 4 cores provide. RPi is just a gnat by comparison. Two million computers? That pales by comparison to the number of set top boxes and DVRs shipped worldwide, which is rising to 125+ Million units in 2017, according to IHS Inc. If the set top box manufacturers have the data they need to design in the SoC from Broadcom, they can churn out 2 orders of magnitude more product than a "gnat" like RPi. At that rate, they could have a dedicated engineer, on the phone 24/7, spoonfeeding the required info to the counterpart at Scientific Atlantic or Huawei, or Pace, or Technicolor....

I seem to detect a lot of defensiveness on the part of RPi "establishment types" regarding what seems to be a totally reasonable request. I for one can imagine an approach which uses a "change document" model to just cover the deltas between the '35 and the '36. If JamesH is correct that there is so little difference, then this should be a quite simple thing. But, if my own analysis is correct, Broadcom doesn't have much motivation to push out a data sheet with any speed.

Instead of getting defensive about there being no datasheet, it would be better to perhaps give everyone the contact info of the Broadcom person who can move off this dime and get something going. A mass communications effort a la a "petition" might impress someone... or maybe not. <sigh> The positive publicity being associated with the very laudable Raspberry Pi community would be good for them. But who knows?
JoGusto
Embedded Systems Engineer
1 Linux x86 Machine with Quadruple boot | 1 Quad core Windows 7 x64 machine
12 Arduinos (Uno, Pro Mini) | 2 Raspberry Pi 2 Mod B's
a few QNX 6.3.2 PowerPC boards

jamesh
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 23879
Joined: Sat Jul 30, 2011 7:41 pm

Re: BCM2836 datasheet

Tue May 19, 2015 8:15 am

You are right that Broadcom really have no incentive to push out a datasheet - it's really spending money for no tangible benefit. And they already do a lot of that simply supported the RPF right now - support they get very little credit for TBH.(Note, I no longer work at Broadcom after being made redundant, so it's not like I have any reasons to like them!).

There are a couple of reasons why people like to keep mobile style SoC's quite secret. Reverse engineering for cloning, and reverse engineering for detecting possible patent infringements. SoC's cost a huge amount of money to produce - many millions of $. Giving your customers a head start of replicating them (or some of the ideas in them) is a bad business decision. And the customers are constantly driving down the price you can charge for them as well, so you really need to maintain any technological benefits you have to keep the prices up enough to actually pay for their development.

For example, I'm working for a chip company, but one of the big problems is customers wanting a particular feature set, who are willing to pay a certain amount, but it is not actually possible to make it for that amount of money! The margins are paper thin in some areas. Any USP is worth holding on to. We are working to try and get the USP, so we can charge a bit more for stuff, so we can actually afford to make it in the first place!
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
Contrary to popular belief, humorous signatures are allowed. Here's an example...
“I think it’s wrong that only one company makes the game Monopoly.” – Steven Wright

ghans
Posts: 7874
Joined: Mon Dec 12, 2011 8:30 pm
Location: Germany

Re: BCM2836 datasheet

Wed May 20, 2015 7:22 am

This is the new peripherials datasheet for the BCM2836 :

https://www.raspberrypi.org/documentati ... rev3.4.pdf


ghans
• Don't like the board ? Missing features ? Change to the prosilver theme ! You can find it in your settings.
• Don't like to search the forum BEFORE posting 'cos it's useless ? Try googling : yoursearchtermshere site:raspberrypi.org

scarschtt
Posts: 3
Joined: Mon Feb 08, 2016 11:46 pm

Re: BCM2836 datasheet

Mon Feb 08, 2016 11:49 pm

Hi, I'm searching for Timer_Arm_count address for the BCM2836, where can i found it?
tnx. :D

internetisalie
Posts: 6
Joined: Fri Jan 01, 2016 10:43 pm

Re: BCM2836 datasheet

Tue Feb 09, 2016 4:18 am

I'm going to guess that you are looking for the generic timer coprocessor registers.

Cortex-A7 ARMv7 Generic Timer:
http://infocenter.arm.com/help/index.js ... IDBIJ.html

More info from Ultibo:
viewtopic.php?f=72&t=135121

FreeBSD driver:
http://web.mit.edu/freebsd/head/sys/arm ... ic_timer.c

Timer count is in either CNTPCT or XXX_TVAL depending on which timer count you want (64-bit upcount, or 32-bit downcount to interrupt, respectively).

Return to “Bare metal, Assembly language”