esp-idf/examples/peripherals/usb/host/cdc/common/cdc_acm_host

USB Host CDC-ACM Class Driver

This directory contains an implementation of a USB CDC-ACM Host Class Driver that is implemented on top of the USB Host Library.

Supported Devices

The CDC-ACM Host driver supports the following types of CDC devices:

1. CDC-ACM devices
2. CDC-like vendor specific devices (usually found on USB to UART bridge devices)

CDC-ACM Devices

The CDC-ACM Class driver supports CDC-ACM devices that meet the following requirements:

• The device class code must be set to the CDC class 0x02 or implement Interface Association Descriptor (IAD)
• The CDC-ACM must contain the following interfaces:
  • A Communication Class Interface containing a management element (EP0) and may also contain a notification element (an interrupt endpoint). The driver will check this interface for CDC Functional Descriptors.
  • A Data Class Interface with two BULK endpoints (IN and OUT). Other transfer types are not supported by the driver

CDC-Like Vendor Specific Devices

The CDC-ACM Class driver supports CDC-like devices that meet the following requirements:

• The device class code must be set to the vendor specific class code 0xFF
• The device needs to provide and interface containing the following endpoints:
  • (Mandatory) Two Bulk endpoints (IN and OUT) for data
  • (Optional) An interrupt endpoint (IN) for the notification element

For CDC-like devices, users are responsible for ensuring that they only call APIs (e.g., cdc_acm_host_send_break()) that are supported by the target device.

Usage

The following steps outline the typical API call pattern of the CDC-ACM Class Driver

1. Install the USB Host Library via usb_host_install()
2. Install the CDC-ACM driver via cdc_acm_host_install()
3. Call cdc_acm_host_open()/cdc_acm_host_open_vendor_specific() to open a target CDC-ACM/CDC-like device. These functions will block until the target device is connected
4. To transmit data, call cdc_acm_host_data_tx_blocking()
5. When data is received, the driver will automatically run the receive data callback
6. An opened device can be closed via cdc_acm_host_close()
7. The CDC-ACM driver can be uninstalled via cdc_acm_host_uninstall()

Examples

• For an example with a CDC-ACM device, refer to cdc_acm_host
• For an example with a CDC-like device, refer to cdc_acm_host_bg96