I2C Slave pulls SDA and SCL Pins low when entering Power Down mode

[lpcware]

Content originally posted in LPCWare by skywalk on Mon Feb 10 09:14:53 MST 2014
I try to test LPC812 power modes and use the LPCXpresso LPC812 Board and the NXP AN11332-Software together with LPCXpresso 6.1.4.

AN11332 Code works until the Device goes to "Power-Down" mode (not Deep-Power-Down).

At this moment, the SDA and SCL pins go low (~0.5 Vdc) voltage.
That disables all other I2C Traffic on the bus and the LPC will never get its Address for waking from Power-Down.
This would make the "wake from I2C" unsuable.

As far as i understand the AN11332 Code, it should work fine; the configuration seems to be OK.

Has somebody used the LPC812 I2C as an Slave and configured it for Power-Down?

/*connect the I2C SCL and SDA sigals to port pins(P0.10-P0.11)*/
regVal = LPC_SWM ->PINASSIGN7 & ~(0xFFUL << 24);
LPC_SWM ->PINASSIGN7 = regVal | (10 << 24); /* P0.10 is I2C SDA, ASSIGN0(31:24) */
regVal = LPC_SWM ->PINASSIGN8 & ~(0xFF << 0);
LPC_SWM ->PINASSIGN8 = regVal | (11 << 0); /* P0.11 is I2C SCL. ASSIGN0(7:0) */

LPC_SYSCON ->CLKOUTDIV = 120; /* CLKOUT = 60E6 / 120 = 500 kHz */
LPC_SYSCON ->CLKOUTSEL = 0x03; /* CLKOUT = Main clock */
LPC_SYSCON ->CLKOUTUEN = 0x01; /* Update CLKOUT Source      */

LPC_GPIO_PORT ->DIR0 |= (1 << 5);
regVal = LPC_SWM ->PINASSIGN8 & ~(0xFF << 16);
LPC_SWM ->PINASSIGN8 = regVal | (0x0F << 16); /* P0.15 is CLKOUT. ASSIGN8(23:16) */

LPC_GPIO_PORT ->DIR0 |= (1 << 7);
SysTick_Config(SystemCoreClock / 2);

/* Enable I2C clock */
LPC_SYSCON ->SYSAHBCLKCTRL |= (1 << 5);
/* Toggle peripheral reset control to I2C, a "1" bring it out of reset. */
LPC_SYSCON ->PRESETCTRL &= ~(0x1 << 6);
LPC_SYSCON ->PRESETCTRL |= (0x1 << 6);

I2C_SlvInit(LPC_I2C, SLAVE_ADDR, CFG_SLVENA, I2C_FMODE_PRE_DIV);
/* Ready to receive the slave address, interrupt(SLAVE ADDR STATE) if match occurs. */
LPC_I2C ->SLVCTL = CTL_SLVCONTINUE;
LPC_I2C ->INTENSET = STAT_SLVPEND;

/* Enable wake from power down using I2C */
LPC_SYSCON ->STARTERP1 |= (1 << 8);

/*****************************************************************************
** Function name:PMU_Sleep
**
** Descriptions:Put some of the peripheral in sleep mode.
**
** parameters:SleepMode: 2 is power down, 1 is deep sleep, 0 is sleep, Sleep peripheral module(s)
** Returned value:None
** 
*****************************************************************************/
void PMU_Sleep( uint32_t SleepMode, uint32_t SleepCtrl )
{
  LPC_SYSCON->PDAWAKECFG = LPC_SYSCON->PDRUNCFG;
  LPC_SYSCON->PDSLEEPCFG = SleepCtrl;
  /* If normal sleep, not deep sleep, don't do anything to SCR reg. */
  switch ( SleepMode )
  {
case MCU_POWER_DOWN:
  SCB->SCR |= NVIC_LP_SLEEPDEEP;
#if __WKT
  LPC_PMU->DPDCTRL |= (0x1 << 2);
  init_wkt(1, 10000 * 10);
#endif
#if 1
  LPC_PMU->PCON = 0x2;
#else
  LPC_SYSCON->PDSLEEPCFG &= 0xFDFF;
#endif
  break;
case MCU_DEEP_SLEEP:
  SCB->SCR |= NVIC_LP_SLEEPDEEP;
#if __WKT
  LPC_PMU->DPDCTRL |= (0x1 << 2);
  init_wkt(1, 10000 * 10);
#endif
#if 1
  LPC_PMU->PCON = 0x1;
#else
  LPC_SYSCON->PDSLEEPCFG &= 0xEFF9;
#endif
  break;
case MCU_SLEEP:
default:
  break;
  }
  __WFI();
  return;
}

[lpcware]

Content originally posted in LPCWare by lpcxpresso-support on Sat Feb 22 07:33:40 MST 2014
Please red this FAQ
http://www.lpcware.com/content/faq/lpcxpresso/compiler-optimization

Especially the section called
Optimized code fails to execute correctly

[lpcware]

Content originally posted in LPCWare by skywalk on Sat Feb 22 02:17:10 MST 2014
Hi,

yes, the CLKOUT is low when entering the power-down mode!

I found that the software works if no optimization is used.

BUT if the software is compiled with optimization for program space ( i need the program space for a FATfs based application), the situation as described in my original post will show up.

As soon as i have found the reason for this behaviour, i will post the result.

[lpcware]

Content originally posted in LPCWare by nxp_apps on Fri Feb 21 14:33:18 MST 2014
Hi,

The application note + software works. Have you monitored the CLKOUT pin to see if the device went into power-down mode?
The observed clock on the CLKOUT pin should go low since all internal clocks are shut down in power-down mode.

In the example code, the command to place the LPC812 into power-down is the I2C slave address 0x54 followed by data byte 0xAA,
I just want to make sure first that the lpc812 went into power-down mode.

Thanks.

nxp_apps