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configtxt/boot: Update arm_64bit flag #3903

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Merged
merged 5 commits into from
Nov 7, 2024
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configtxt/boot: Update arm_64bit flag #3903

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configtxt/boot: Update arm_64bit flag
tdewey-rpi Nov 4, 2024
4270c31
Move Raspberry Pi 5 warning to start of block
tdewey-rpi Nov 5, 2024
4835557
Suggested rewording from Nate
tdewey-rpi Nov 7, 2024
6349bd0
Prune top-heavy NOTE
tdewey-rpi Nov 7, 2024
e82addc
Add CM4S
nathan-contino Nov 7, 2024
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2 changes: 1 addition & 1 deletion documentation/asciidoc/computers/config_txt/boot.adoc
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Expand Up @@ -29,7 +29,7 @@ If set to 1, the kernel will be started in 64-bit mode. Setting to 0 selects 32-

In 64-bit mode, the firmware will choose an appropriate kernel (e.g. `kernel8.img`), unless there is an explicit `kernel` option defined, in which case that is used instead.

Defaults to 1 on Pi 4s (Pi 4B, Pi 400, CM4 and CM4S), and 0 on all other platforms. However, if the name given in an explicit `kernel` option matches one of the known kernels then `arm_64bit` will be set accordingly.
Defaults to 1 on Raspberry Pi 4, 5, 400 and Compute Module 4, 4S platforms. Defaults to 0 on all other platforms. However, if the name given in an explicit `kernel` option matches one of the known kernels then `arm_64bit` will be set accordingly.
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I'd add CM5 as well - everyone knows its coming.

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I try to avoid mentioning any potential products ahead of a formal announcement, especially if I've structured the text such that any new products could be trivially included in the line.

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Agree with Tom in principle. But for my own edification: I assumed that CM5 wouldn't support 32-bit mode at all, just like Pi 5. So I don't think we need to add it here at release. Is that correct, @JamesH65 ? Or will CM5 support 32-bit mode?

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I believe it's actually the SoC (and not the specific Model) that determines if it's capable of booting 32-bit kernel only (BCM2835, BCM2836), either 32- or 64-bit kernel (BCM2837, RP3A0, BCM2711), or 64-bit kernel only (BCM2712) ?

But (in general) we explicitly list the Models in documentation rather than SoCs, because people find it easier to identify their Model than to identify their SoC 🧦 😉


NOTE: 64-bit kernels may be uncompressed image files or a gzip archive of an image (which can still be called kernel8.img; the bootloader will recognize the archive from the signature bytes at the beginning). The 64-bit kernel will only work on the Raspberry Pi 3, 3+, 4, 400, Zero 2 W and 2B rev 1.2, and Raspberry Pi Compute Modules 3, 3+ and 4. Raspberry Pi 5 only supports a 64-bit kernel, so this parameter has been removed for that device.

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