Raspberry Pi 上的 Ubuntu 19.10 具有/启动/固件/自述文件陈述如下：
An overview of the files on the /boot/firmware partition (the 1st partition
on the SD card) used by the Ubuntu boot process (roughly in order) is as
follows:
* bootcode.bin - this is the second stage bootloader loaded by all pis with
the exception of the pi4 (where this is replaced by flash
memory)
* config.txt - the first configuration file read by the boot process
* syscfg.txt - the file in which system modified configuration will be
placed, included by config.txt
* usercfg.txt - the file in which user modified configuration should be
placed, included by config.txt
⋯
include syscfg.txt
include usercfg.txt
还，/boot/firmware/config.txt顶部有以下通知：
# Please DO NOT modify this file; if you need to modify the boot config, the
# "usercfg.txt" file is the place to include user changes. Please refer to
# the README file for a description of the various configuration files on
# the boot partition.
但是，任何配置指令放在/boot/firmware/usercfg.txt，例如gpu_mem=16，在启动时会被忽略。
我熟悉使用/boot/config.txt在 Raspbian 下，所有固件配置指令都放在这个单独的文件中，并且不支持“include”指令。
Ubuntu 似乎已经扩展了此机制，大概是通过使用 uboot，通过添加“include”并将配置拆分为多个文件，但这似乎不起作用。我仍然必须将指令添加到 config.txt 文件才能使它们生效。
有人能解释一下吗？