1. Home
  2. Embedded Programming
  3. USB transfer rate LPC17xx

USB transfer rate LPC17xx

Hi, We are designing a device which needs to transfer data to a PC over USB continuously. We plan to use the LPC1768 Cortex-M3 processor for this application. We would like some opinion on the best approach for the USB class implementation. We are looking at about 400Kbytes/sec sustainable transfer rate between the device to PC. The reverse traffic will be quite lean.

We were thinking of using the USB CDC since it uses bulk transfers & hence could provide good throughputs. Has anyone tried measuring the max. throughputs using the USB CDC driver? Your opinions would be most appreciated.

--------------------------------------- Posted through

formatting link

Reply to
navman
Loading thread data ...

We get over 500KB/s with a 32mHz PIC24, so M3 should be doable. However, we are using asynchronous ACK/NAK protocols.

e

CDC VCP management on the PC is a mess. Just use bulk transfers directly with Async. ACK/NAK.

Reply to
linnix

I don't think that you mean that do you? USB 2.0 high speed can manage a maximum 480Mbps but the actual rate is less allowing for turn-arounds, inter-packet gaps, etc.

Andrew

Reply to
Andrew Jackson

I've achieved 120Mbps through an RNDIS device to a PC and > ~200Mbps with a custom bulk driver (FX2LP). This is /roughly/ equivalent to CDC. However 400kbytes/second isn't physically possible on a high-speed USB

2.0 device: the maximum is 480Mbps. What is your actual transfer speed requirement?

Andrew

Reply to
Andrew Jackson

B

SB

e

ite

Yes, full speed bandwidth is 12M, 500K is around 4M.

That why we need asynch. bulk transfer. Max. transfer is to internal SRAM only, 96K for 1/5 of a second.

Reply to
linnix

Sorry that'll teach me not to reply last thing at night. 400KBps =

3200kbps = 3.2Mbps so well within USB 2.0 capabilities!

Andrew

Reply to
Andrew Jackson

Apologies, brain fade!

Andrew

Reply to
Andrew Jackson

USB

Seems like you may have read some decimal points or scale factors in the wrong place. At first blush the 400Kbytes/sec multiplies out to 3.3Mbits/sec, which even considering that framing and handshaking overhead is not considered, is a whole lot lower than the max rate of Full speed port then yet the High speed port.

--

Michael Karas
Carousel Design Solutions
http://www.carousel-design.com
Reply to
Michael Karas

Unfortunately, we do not have time to play around with the USB driver code (both on LPC17xx side and PC side) and have to live with whatever examples we have from NXP, LPCexpross & such as we need to focus more on the application which is huge. So can you guys share some information on practical achievable transfer speeds from LPC to PC using USB CDC class drivers?

--------------------------------------- Posted through

formatting link

Reply to
navman

e
s

It depends on your implementations. Yes, CDC allows networking layers; for example: ATM over USB. However, they are usually very specific to the applications. I have not seen any general CDC NET example from Atmel, Microchip or NXP. Most of the CDC examples are tied to the serial port. So, you are pretty much on your own with CDC NET.

That's why we pick ADB over USB. At least there are existing drivers for Linux and Window, and the basic protocols are well defined and published. However, as always, there are issues for the final 10% of implementations.

Reply to
linnix

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.