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I just acquired a Raspberry Pi 4 Model B with 4GB RAM. The processor stepping (revision) is B0 (the heat spreader says 2711ZPKFSB06B0T). It seems to be stable at 2.0 GHz with over_voltage=6; it'll hang during stress tests at 2.15 GHz, and the Raspberry Pi OS desktop will not load at all at 2.2 GHz.

However, I've read that the Compute Module 4 and Raspberry Pi 400 use the C0 stepping of the BCM2711 (2711ZPKFSB06C0T), which, among other things, runs cooler and has higher overclocking potential.

Aside from the performance and efficiency differences, are there any other differences between these steppings, such as processor errata fixes?

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As far as I can tell from anything public, there are a few fixes but nothing major and certainly nothing that's affected even the weird stuff I've been testing on the CM4.

The major difference seems to be that thermals are slightly better on the C0—I can run these things for days at base clock and they don't overheat, even with constrained airflow, unlike the Pi 4 model B.

The two other things I have seen confirmed fixed in the C0 have to do with memory addressing for Pis with 4+ GB of RAM:

  • The EMMC2 bus can only directly address the first 1GB.
  • The PCIe interface can only directly address the first 3GB.

I should note that even among different C0 units, some can handle overclocking better than others (assuming adequate cooling with a proper heatsink and fan). Some CM4s I can get up to 2.3 GHz, others start failing to boot beyond 2.0 GHz. All of them take 1.8 GHz just fine though (and that's probably why the Pi Foundation kept the Pi 400 clocked at that speed).

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Raspberry Pi 4 model B also had the upgrade from B0 to C0, without a mention from the Raspberry foundation. That means that the latest batch we've received of Raspberry Pi's of the same exact model, were actually featuring a different CPU, which broke our bootloader (!!!).

See this thread for more info about the difference between the two CPUs and this patch for u-boot in case you're using it.

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