Default rpiboot mass-storage payload fails on CM4 eMMC writes; explicit -d mass-storage-gadget64 works

Start with the default payload used by ./rpiboot -v and compare it with mass-storage-gadget64/boot.img, config.txt, and bootfiles.bin, especially the listed boot_ramdisk=1 and uart_2ndstage=1 settings. Reproduce the CM4 eMMC write test, then verify that the default payload behaves like the explicit mass-storage-gadget64 payload without causing the USB device to disconnect.

Describe the bug

Hardware:

• Raspberry Pi Compute Module 4 with 16 GB eMMC
• Raspberry Pi Compute Module 4 IO Board
• Host: Linux Mint
• Also reproduced on a Windows 11 PC
• Different USB cables and USB ports tested

usbboot:

• local build
• build-date: 2026/08/12
• pkg-version: local 87d6e032

Problem:
When starting rpiboot without specifying a directory:

sudo ./rpiboot -v

the CM4 eMMC appears as:

/dev/sdb
30535680 512-byte logical blocks
Write Protect is off

Reading works, but writing causes the USB mass-storage device
to disappear. For example:

sudo dd if=/dev/zero of=/dev/sdb bs=1M count=100 conv=fsync

results in USB errors such as:

device descriptor read/64, error -110
Device not responding to setup address
device not accepting address ..., error -71
USB disconnect
device offline error, dev sdb

A read test worked:

sudo dd if=/dev/sdb of=/dev/null bs=4M count=100

419430400 bytes ... 10.3 MB/s

However, explicitly using the current mass-storage-gadget64
directory fixes the problem:

sudo ./rpiboot -d ./mass-storage-gadget64 -v

With this payload:

sudo dd if=/dev/zero of=/dev/sdb bs=4096 count=1 oflag=direct

works.

A larger test also succeeds:

sudo dd if=/dev/zero of=/dev/sdb bs=1M count=1024 oflag=direct

1073741824 bytes ... 24.9 MB/s

The RPi Imager then also works normally.

The explicit payload contains:

mass-storage-gadget64/boot.img
mass-storage-gadget64/config.txt
mass-storage-gadget64/bootfiles.bin

The config contains:

boot_ramdisk=1
uart_2ndstage=1

It looks like the default/embedded mass-storage-gadget payload
may differ from the current mass-storage-gadget64 payload, and
the former has a write-path problem on CM4 eMMC.

Steps to reproduce the behaviour

./rpiboot
→ eMMC reads OK
→ eMMC writes cause USB disconnect

./rpiboot -d ./mass-storage-gadget64
→ eMMC reads OK
→ eMMC writes work normally (~25 MB/s)

Device(s)

Raspberry Pi CM4

Compute Module IO board.

• Raspberry Pi Compute Module 4 with 16 GB eMMC
• Raspberry Pi Compute Module 4 IO Board

RPIBOOT logs

No response

Kernel logs

No response

Device UART logs

No response