AHB SRAM or loading cause CDC/VCOM USB stop working in LPC4337

[lpcware]

Content originally posted in LPCWare by jpplus on Thu Dec 11 01:55:48 MST 2014
I am using the ROM API CDC VCOM to develop a 4337 USB application.
The observations are:
1) when any code like memcpy access the AHB SRAM, USB stops working
2) when system loading is high, USB stop working. I have a DMA interrupt handler, USB can work correctly. But after I add more codes (basically computation complex stuff) in context of IRQ. Then USB stops.
USB stops means USB device show as a serial port in PC, and I uses some console app like Putty to receice data from this USB virutal serial port, but after accessing the AHB SRAM or adding computation complex stuff, there is no data can be receiced from Putty.

it is very strange, any ideas or hints are welcome.

[lpcware]

Content originally posted in LPCWare by Tsuneo on Thu Dec 11 08:57:03 MST 2014

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Quote:
1) when any code like memcpy access the AHB SRAM, USB stops working

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If you are using the first AHB SRAM space starting from 0x2000 0000 for other purpose, assign another bank of AHB SRAM (0x2000 8000) to the working space of the USB ROM API, so that DMAs work simultaneously over the multi-layer AHB matrix.

  usb_param.mem_base = 0x20008000;

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Quote:
But after I add more codes (basically computation complex stuff) in context of IRQ. Then USB stops.

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USB ROM API is also driven by interrupt.
Assign higher priority to the USB interrupt than the interrupt of your complex stuff.

Tsuneo