[vfs_tinyusb] static struct cause register twice missing the first (IEC-397)

[kaidegit]

Answers checklist.

• I have read the component documentation ESP-IDF Components and the issue is not addressed there.
• I am using target and esp-idf version as defined in component's idf_component.yml
• I have searched the issue tracker for a similar issue and not found any related issue.

Which component are you using? If you choose Other, provide details in More Information.

device/esp_tinyusb

ESP-IDF version.

release/v5.4

Development Kit.

ESP32S3-Devkit

Used Component version.

1.7.6~2

More Information.

When call the vfs reg func twice, it will only output with the last one.

    tinyusb_config_cdcacm_t acm_cfg = {
        .usb_dev = 0,
        .cdc_port = TINYUSB_CDC_ACM_0,
        .callback_rx = NULL,
        .callback_rx_wanted_char = NULL,
        .callback_line_state_changed = NULL,
        .callback_line_coding_changed = NULL
    };
    ESP_ERROR_CHECK(tusb_cdc_acm_init(&acm_cfg));

    acm_cfg.cdc_port = TINYUSB_CDC_ACM_1;
    ESP_ERROR_CHECK(tusb_cdc_acm_init(&acm_cfg));

    esp_vfs_tusb_cdc_register(TINYUSB_CDC_ACM_0, path_0);
    esp_vfs_tusb_cdc_register(TINYUSB_CDC_ACM_1, path_1);

    const char* path = path_0;
    ESP_LOGI(TAG, "stdio -> %s", path);
    stdin = fopen(path, "r");
    stdout = fopen(path, "w");
    stderr = stdout;

    while (1) {
       // output in the path_1 cdc port
        ESP_LOGI(TAG, "%s: hello world", path);
        vTaskDelay(pdMS_TO_TICKS(1000));
    }

[github-actions]

Hi @kaidegit! Please be aware that the following suggestions are generated by a bot and haven't been fact-checked by Espressif Systems. We hope that this message will help you until an Espressif Engineer looks at your issue.

---

Thank you for providing detailed information and code. Based on the knowledge sources, here’s what can be confirmed about registering multiple CDC ACM ports with VFS using esp_tinyusb and ESP-IDF:

Key Points from Documentation

• The TinyUSB CDC-ACM device can be initialized for multiple ports by setting .cdc_port in the tinyusb_config_cdcacm_t structure and calling tusb_cdc_acm_init() for each port.
• To register each CDC port with the VFS, you should call esp_vfs_tusb_cdc_register() for each port and path.
• The documentation and examples show that it is possible to register multiple CDC ports, each with its own VFS path, and use them independently. However, there is no explicit example or guarantee in the official documentation that standard I/O redirection (stdin/stdout/stderr) to one VFS path will not affect the other, or that both can be used simultaneously for output in the way you expect.

Your Issue

You observed that after registering two CDC ports and their VFS paths, output only appears on the last registered port/path, even when you open the first path for stdout. This suggests that the VFS or TinyUSB CDC-ACM implementation may only support one active output stream at a time, or that the underlying driver is overwriting the previous registration.

Documentation Gaps

• The official documentation for USB Serial Device (CDC-ACM) and esp_tinyusb describes how to initialize and register a CDC-ACM device, but does not explicitly address the behavior when registering multiple CDC ports with VFS or how standard I/O redirection interacts with multiple ports.
• There is no explicit mention of limitations or expected behavior when registering multiple CDC ports with VFS in the available documentation.

Conclusion

Based on the available knowledge sources, it appears that registering multiple CDC ports with VFS is supported at the API level, but the observed behavior (output only on the last registered port) may be due to an internal limitation or a bug in the esp_tinyusb or VFS implementation. The documentation does not provide enough detail to confirm whether this is expected or how to work around it.

Recommendation:
This issue may require further investigation by the Espressif USB or VFS maintainers. Please consider opening an issue on the esp-usb GitHub repository with your findings and code example, as this may be a limitation or bug not covered in the current documentation.

If you need to use multiple CDC ports simultaneously, you may need to manage the file descriptors and output streams at the application level, or wait for clarification or a fix from the maintainers.

---

References:

• USB Serial Device (CDC-ACM) API Reference
• esp_tinyusb component documentation

If you need further assistance, please let us know!

[tore-espressif]

Hello @kaidegit,
you are correct — this is a current limitation of the CDC VFS driver. At the moment, we do not have plans to implement this functionality. However, if you could share more details about your intended use case and why this feature is important for your application, we can reconsider its priority for future development.

[kaidegit]

Just notice this when testing example...

My application use one vfs, and control the other by my callback. So, it is not quite important for me that only suppot one.