Having problems with optimisation on your USB project?

lpcware — Wed, 15 Jun 2016 23:31:38 GMT

Content originally posted in LPCWare by leo738 on Fri May 16 14:49:23 MST 2014
Hello All,

I've been working on a USB project & was tweaking as I was finishing up. I found invoking the minimal level of optimisation caused the USB functionality to fail. After some searching I've tracked down the culprit to a delay function in usbhw.c. This file has the header:

/*----------------------------------------------------------------------------
 *      U S B  -  K e r n e l
 *----------------------------------------------------------------------------
 * Name:    usbhw.c
 * Purpose: USB Hardware Layer Module for NXP LPC17xx
 * Version: V1.20
 *----------------------------------------------------------------------------
 *      This software is supplied "AS IS" without any warranties, express,
 *      implied or statutory, including but not limited to the implied
 *      warranties of fitness for purpose, satisfactory quality and
 *      noninfringement. Keil extends you a royalty-free right to reproduce
 *      and distribute executable files created using this software for use
 *      on NXP Semiconductors LPC microcontroller devices only. Nothing else 
 *      gives you the right to use this software.
 *
 * Copyright (c) 2009 Keil - An ARM Company. All rights reserved.
 *----------------------------------------------------------------------------
 * History:
 *          V1.20 Added USB_ClearEPBuf
 *          V1.00 Initial Version
 *----------------------------------------------------------------------------*/

& the function in particular:

void delay (uint32_t length ) {
  volatile uint32_t i;// changed to volatile to prevent removal by optimisation

  for ( i = 0; i < length; i++ );
  return;
}

Changing i to a volatile data type caused the USB functionality to work again.

A little surprised that this hasn't appeared elsewhere before, but hope it helps somebody else!

Leo

topic Having problems with optimisation on your USB project? in LPCXpresso IDE

Having problems with optimisation on your USB project?