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GD32F10x User Manual
756
23.6.
Function overview
23.6.1.
USB endpoints
USBD supports 8 USB endpoints that can be individually configured.
Each endpoint supports:
Single/Double buffer (endpoint 0 can’t use double buffer).
One endpoint buffer descriptor.
Programmable buffer starting address and buffer length.
Configurable response to a packet.
Control transfer (endpoint 0 only).
Endpoint buffer
The function of the device operation is to transfer a request in the memory image to and from
the Universal Serial Bus. To efficiently manage USB endpoint communications, USBD
implements a dedicated data packet buffer of 512-bytes SRAM memory accessed directly by
the USB peripheral.
It is mapped to the APB1 peripheral memory, from 0x4000 6000 to
0x4000 6400. The total capacity is 1KB, but USBD uses actually only 512 bytes for the bus
width reason.
Each endpoint can be associated with one or two data packet buffers used to store the current
data payload. The bidirectional endpoint has usually two buffers, one is used for transmission
and the other one is for reception. The mono-directional endpoint only has one buffer for data
operation.
Note:
The USBD and CAN share the dedicated 512-byte SRAM memory.
Endpoint buffer descriptor table
USBD implements an endpoint buffer descriptor table which defines the buffer address and
length and which is also located in the endpoint data packet buffer. The endpoint buffer
descriptor is used as a communication port between the application firmware and the SIE in
system memory. Every endpoint direction requires two 16-bit words buffer descriptor.
Therefore, each table entry includes 4 16-bit words (Tx and Rx two direction) and is aligned
to 8-byte boundary. When an endpoint is double-buffered, the SIE will use the two buffers in
ping-pong operation mode. The endpoint buffer descriptor table is pointed to by the USBD
endpoint buffer address register.
The relationship between endpoint buffer descriptor table entries and packet buffer areas is
depicted in
Figure 23-2. An example with buffer descriptor table usage (USBD_BADDR
Содержание GD32F10 Series
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