CH32 USB Implementation

CH32 provides three kinds of USB peripherals as shown below.
For devices with a hardware Unique ID (UID) such as CH32V2/V3, it is recommended to derive the USB device serial number from the chip UID and pass it to the USB device constructor as a {pointer, length} pair.

Name	Role	Bidirectional Endpoints	Double Buffering	DMA Support
USB_DEVICE (not yet supported)	Device	HW double buffer not bidirectional	Software/Hardware	Not supported
USBHS	Host/Device	HW double buffer not bidirectional	Hardware double buffer	Supported
USBFS	Host/Device	Bidirectional	Hardware double buffer	Supported

Note: On common CH32V2/V3 parts, the UID is 96 bits (12 bytes) and can be read from 0x1FFFF7E8 as a contiguous 12-byte block.

USBFS

CH32 USBFS only supports declaring endpoints in the following way. For non-EP0 endpoints, a buffer size of 128 bytes is recommended:

1. {{ep0_buffer}, ...}: pass the buffers directly. Except for EP0, each entry will be split into IN/OUT buffers. Endpoint numbers auto-increment.

LibXR::CH32USBDeviceFS usb_dev(
    /* EP */
    {
        {ep0_buffer},
        {ep1_buffer},
        {ep2_buffer},
    },
    /* packet size */
    LibXR::USB::DeviceDescriptor::PacketSize0::SIZE_64,
    /* vid pid bcd */
    0x1209, 0x0001, 0x0100,
    /* language */
    {&LANG_PACK_EN_US},
    /* config */
    {{&cdc1}},
    /* Serial Number UID (12 bytes read from CH32 UID at 0x1FFFF7E8) */
    {reinterpret_cast<void*>(0x1FFFF7E8), 12});

USBHS

CH32 USBHS supports three endpoint declaration styles. For non-EP0 endpoints, a buffer size of 1024 bytes is recommended. Endpoint numbers auto-increment:

1. {ep0_buffer_hs}: pass the EP0 buffer directly.
2. {ep1_buffer_tx_hs, true}: pass the buffer and enable double buffering
   • ep1_buffer_tx_hs: buffer for the EP1 endpoint
   • true: whether this endpoint is configured as IN
3. {ep2_buffer_rx_hs, ep2_buffer_tx_hs}: pass buffers for a bidirectional endpoint without enabling double buffering

LibXR::CH32USBDeviceHS usb_dev_hs(
    /* EP */
    {
        {ep0_buf_hs},                    // EP0
        {ep1_in_buf_hs, true},           // EP1 IN (unidirectional, double-buffered)
        {ep2_out_buf_hs, false},         // EP2 OUT (unidirectional, double-buffered)
        {ep3_out_buf_hs, ep3_in_buf_hs}  // EP3 bidirectional (no double buffer)
    },
    /* vid pid bcd */
    0x1209, 0x0001, 0x0100,
    /* language */
    {&LANG_PACK_EN_US},
    /* config */
    {{&cdc2}},
    /* Serial Number UID (12 bytes read from CH32 UID at 0x1FFFF7E8) */
    {reinterpret_cast<void*>(0x1FFFF7E8), 12});