%T#13888 Task opened by 74R3D: iPod Classic USB mass storage playback corruption on Yamaha CD-S303

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A new Flyspray task has been opened.  Details are below. 

User who did this - Jared Golubarsch (74R3D) 

Attached to Project - Rockbox
Summary - iPod Classic USB mass storage playback corruption on Yamaha CD-S303
Task Type - Bugs
Category - USB operation
Status - Unconfirmed
Assigned To - 
Operating System - iPod Classic
Severity - Medium
Priority - Very Low
Reported Version - Release 4.0
Due in Version - Undecided
Due Date - Undecided
Details - **Target or Device:**
iPod Classic 7th Gen / Late 2009 160GB, Model MC297, running Rockbox.

The issue was reproduced on two different iPod Classic devices:

1. iPod Classic with iFlash / SD storage
2. iPod Classic with original HDD

USB HID is disabled.
Filesystem is FAT32.
Multiple USB cables were tested, including a shortened approx. 10 cm cable.
The same issue occurs regardless of cable and storage type.

**Release or version:**
`f886bfc572-260502`
Target: `ipod6g`
Features include: `usbstack`, `usb_hid`, `usbdac`

**Host device:**
Yamaha CD-S303 CD player / USB host

**Steps to reproduce:**

1. Install Rockbox on an iPod Classic and disable USB HID.
2. Copy a small test folder to the iPod containing:

   * MP3 320 kbps
   * AAC-LC
   * FLAC 16-bit / 44.1 kHz
   * WAV PCM 16-bit / 44.1 kHz
3. Connect the Rockbox iPod via USB to a Yamaha CD-S303.
4. Start playback from the Yamaha’s USB media browser.
5. Compare the result with the same files copied to a normal FAT32 USB flash drive and played on the same Yamaha CD-S303.

**Expected result:**
The Yamaha CD-S303 should play the files from the Rockbox iPod correctly, as it does from a normal USB flash drive.

**Actual result:**
The Yamaha detects the Rockbox iPod as a USB mass storage device and playback starts, but audio playback is corrupted for several formats.

Observed behavior:

* MP3 playback appears to work normally or much better.
* FLAC 16/44.1 starts playing, but has periodic severe distortion/dropouts. File tags are not displayed correctly.
* WAV PCM 16/44.1 plays continuously and tags/metadata are displayed, but the audio is permanently distorted, as if the PCM sample data is being read or interpreted incorrectly.
* AAC also shows playback issues.
* The same files play correctly from a normal FAT32 USB flash drive on the same Yamaha CD-S303.
* Files copied back from the iPod to a USB flash drive play correctly, so the files do not appear to be corrupted on storage.
* The issue occurs both with iFlash/SD storage and with an original HDD iPod, so the storage adapter is unlikely to be the cause.
* The issue is unchanged with a very short USB cable, so cable length is unlikely to be the cause.
* USB HID is disabled, so this does not appear to be caused by HID/composite-device behavior.

**Current hypothesis:**
This appears to be a USB Mass Storage interoperability issue between Rockbox on iPod Classic and the Yamaha CD-S303 USB host, rather than an audio codec issue. In this setup, the iPod is not decoding the audio; the Yamaha reads the files from the iPod as mass storage and decodes them itself.

Possible areas to investigate:

* USB Mass Storage behavior in `firmware/usbstack/usb_storage.c`
* SCSI `READ_10` / `READ_16`
* `READ_CAPACITY` / `MODE_SENSE`
* transfer size / read buffer behavior
* block size / sector size reporting
* iPod Classic configuration in `firmware/export/config/ipod6g.h`

A possible mitigation might be an optional USB mass storage compatibility mode for strict embedded USB hosts, for example using smaller transfer sizes or more conservative sector/block reporting.



More information can be found at the following URL:
https://www.rockbox.org/tracker/task/13888

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