Rpi4B & Pi Zero 2W -- each a different Broadcom

[John Laurence Poole]

I have a project where I am using the Raspberry Pi 4B ("Rpi4B") to build-out an image of Gentoo Linux developed by the GenPi64 project.  The image appears to work, so far, on both the Rpi4B and the Pi Zero 2 W ("PiZero2W").  Since the Pi Zero has only 500 MB or ram, and my Rpi4B has 8 GB or ram and a faster processor, I find I can add packages through Gentoo's emerge facility running on the Rpi4 without problems such as I might encounter with the RAM limitations of the PiZero2W.  For instance, I'll be using Zerotier, and compiling it on the PiZero2W brought the unit to its knees; when I compiled it on the Rpi4B, it was about 5 minutes, an often consuming memory just below 1.5 GB.    I also installed Gentoo's package dev-libs/bcm2835 and just logged a bug to bump the version to 1.73.  I then started to consider and then learned that each Raspberry Pi model may have difference Broadcom chips, and determined the following:

PiZero2W has:
    Instruction set: ARMv8-A (64/32-bit)
    Processor: 4× Cortex-A53 1 GHz
    Broadcom BCM2710A1

Rpi4B has:
    Instruction set: ARMv8-A (64/32-bit)
    Processor: 4× Cortex-A72 1.5 GHz or 1.8 GHz[23]
    Broadcom BCM2711

Source: Wikipedia

So I searched this group for both Broadcom chip numbers and did not find much activity for the 2710A1 or 2711.  Are there any other projects or groups that work on supporting those two chips?  I suspect not, but want to make sure I'm not missing something.  Would there be anything in the works for those two chips?  Assuming there is not, my approach would be to determine what services/pins are going to be used by my project (aircraft decibel monitoring in residential areas near an airport) and then assess them in the context of the 2835, 2710A1 and 2711.

Thank you,

John

[John Laurence Poole]

This reply will essentially answer my own question.

On a more careful reading of https://www.raspberrypi.com/documentation/computers/processors.html, BCM 2835 "is identical to" BCM 2836 which is "is identical to" BCM2837.  Then the Rpi4B's BCM2711 is "considerable upgrade", but nothing seems to negate prior features, just has faster and more features.  The RP3A0's BCM2710A1 is the silicon die packaged inside the Broadcom BCM2837, and then there is the "Please refer to the following BCM2836 document for details on the ARM peripherals specification, which also applies to the BCM2837 and RP3A0" which suggests no major changes.  Though, as I surveyed some of the postings in this list, it looks like there might be some differences, so a careful survey after I determine what services I'll end up using is warranted.

Notes:

1) BCM2835
    Raspberry Pi 1 Models A, A+, B, B+, the Raspberry Pi Zero, the Raspberry Pi Zero W

2) BCM2836    
    The underlying architecture in BCM2836 is identical to BCM2835. The only significant difference is the removal of the ARM1176JZF-S processor and replacement with a quad-core Cortex-A7 cluster.
   

3) BCM2837
    Raspberry Pi 3 Model B, later models of the Raspberry Pi 2 Model B, and the Raspberry Pi Compute Module 3. The underlying architecture of the BCM2837 is identical to the BCM2836. The only significant difference is the replacement of the ARMv7 quad core cluster with a quad-core ARM Cortex A53 (ARMv8) cluster.
   
...
5) BCM2711
    Raspberry Pi 4 Model B, the Raspberry Pi 400, and the Raspberry Pi Compute Module 4.   BCM2711 is a considerable upgrade on that used by the SoCs in earlier Raspberry Pi models. It continues the quad-core CPU design of the BCM2837, but uses the more powerful ARM A72 core. It has a greatly improved GPU feature set with much faster input/output, due to the incorporation of a PCIe link that connects the USB 2 and USB 3 ports, and a natively attached Ethernet controller. It is also capable of addressing more memory than the SoCs used before.
   
6) RP3A0
    The Raspberry Pi RP3A0 is our first System-in-Package (SiP) consisting of a Broadcom BCM2710A1 — which is the silicon die packaged inside the Broadcom BCM2837 chip which is used on the Raspberry Pi 3 — along with 512MB of DRAM.

    It is used by the Raspberry Pi Zero 2 W.
   
    Please refer to the following BCM2836 document for details on the ARM peripherals specification, which also applies to the BCM2837 and RP3A0.

[Simon Peacock]

Technically, you shouldn't need to care any more than what the pin number is.  The Hardware Abstraction Layer should handle this for you.  If you found a bug, check if it's not a "feature" and get it fixed, then just use the HAL functions to do the interface.

To let you know... Broadcom don't hand out information freely, so you won't see much from them, stick to the official PI channels, who will get all the info, and won't necessarily be burdened with all the NDA's.

Simon

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