CODEWITHSUNDEEP
usbstm32cdc
Mohammad
Mohammad

Reputation: 89

What is the maximum speed of the STM32 USB CDC?

I'm using an STM32L151 to communicate with a PC using USB CDC. I used the STM32 HAL libraries to create my project. I found that the USB sends data in 1 ms intervals, and each time 64 bytes are being sent. So, is the maximum speed of the USB CDC 64 kbyte/s? That is much lower than the USB Full Speed data rate of 12 Mbit/s. How can I reach this speed, or at least a fraction of this speed?

Upvotes: 9

Views: 24771

Answers (2)

0___________
0___________

Reputation: 67476

  1. USB FS frame is 1ms so if you put 64 bytes to the buffer (using the HAL function) - it will send those 64 bytes in the next frame. And it will not send any more data until another 1ms frame

  2. How to increase this speed -> aggregate your data in larger chunks and send more data in the one transaction (up to 8kB using HAL libraries).

Upvotes: 4

Turbo J
Turbo J

Reputation: 7691

Nope. If your code is "fast enough", the maximum CDC speed is about 1MByte/sec. This may require a big (>1KB) FIFO on the device side. Oh, and the PC side must be able to read the data fast enough, e.g. with big buffers.

The 64KByte/s limit applies for USB HID which uses interrupt endpoints. USB CDC interface uses faster bulk endpoints.

Upvotes: 10

Related Questions