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I've seen the System on Chip of Raspberry Pi referred to usually as "BCM2835" (e.g. on Wikipedia), but sometimes as "BCM2708" (e.g. sources for Linux SPI driver are in bcm2708.c, or in comments to my other question).
Which is right, or are both - why? Specially, if there are inconsistencies in datasheets for both, which shall be understood as "more important"?
Actually the discrepancy is due to the designation of the silicon and the chip package. Originally there was the silicon die which is known as BCM2708, all initial development was done around this.
In a stacked 9x9 package with 256MB of DRAM it is then known as BCM2763. (Stacked is when you literally bond the DRAM silicon on top of the processor and put bond wires down onto the substrate)
But when the memory is POP'd (package on package, the DRAM package is attached to the top of the processor package) then it was known as BCM2835, this is the device that then had the ARM enabled.
Later versions of the chip follow the same scheme, there are now three pieces of silicon, BCM2708, BCM2709 and BCM2710 and three packages BCM2835, BCM2836 and BCM2837.
Further to Steve's answer, there is a discussion here on the git hub issue log for linux drivers discussing how the drivers should be labeled. The pertinent posts are:
popcornmix:
Technically 2708 is the family, and 2835 is a specific implementation. We now know that 2835 is the only implementation in the family that can run linux, (and there won't be new models of this family), so it probably doesn't matter which model is used, although it should be consistent.
lp0:
So it would be reasonable to name all the drivers 2708 but the specific device tree file 2835? (assuming that if there is ever another model of that family that can run linux it would need a different list of devices)
Technically 2708 is the name for the family of chips, and 2835 is the specific chip in the Pi. As to which datasheet supersedes the other, I would chose the BCM2835 (specific) over the BCM2708 (family).
It is worth realizing that the ARM core is not a primary part of the SoC, but an auxiliary core stuck on the side, behind a system MMU. The main (boot) processor is the VideoCore, which performs early initialization, sets up the system MMU and boots up the ARM core.
Most likely bcm2708 refers to the main part of the SoC containing the VideoCore processor and peripherals (look at wikipedia's table of VideoCore SoCs, notice how no bcm27xx part has an ARM core).
Based on broadcom's driver source code release, I actually get the impression all VC4 SoCs are based on the bcm2708, while VC3 is bcm2707. There are are at least three bcm2708 revisions (a0, b0, c0) though, and a0 differs sufficiently to have #ifdefs all over the place and quite a few headers of its own. There's also an exception for "VC4 big island" whose main header is not included, but I can't really find much about it, although this remark is an interesting one.
So it makes sense for drivers to be referring to the 2708 (especially if they were developed by broadcom).
I'm not sure what to make of the rpi2 reporting bcm2709... there are numerous statements that the bcm2835 and bcm2836 SoCs differ only in the ARM subsystem and the peripheral base address (i.e. slightly different system MMU config), so it seems highly likely it is in fact also bcm2708 based, but the info available is rather limited. I wonder if someone just bumped the number to deal with code that assumes bcm2708 implies an ARM11 core (while in fact it doesn't imply any ARM core at all).
Edit: The newly released bcm2836 quad-A7 doc confirms it is also based on the bcm2708.
My search for this question was prompted by this page
Note the response from command cat /proc/cpuinfo
...
Hardware : BCM2708
Revision : 1000002
