TMDSCNCD280049C: GPIO_setQualificationPeriod function

Hi,

The TRM section "Input qualification" under GPIO chapter talks more about this. Did you get a chance to look at it?

Regards,

Veena

Dear Veena

In an effort to understand the DEVICE_DELAY_US()  macro, I've altered one of the example programs.  Please see snippet. 

//
// Set GPIO16
//
GPIO_writePin(16, 1);

//
// Wait for Qual period
//
DEVICE_DELAY_US(DELAY);

//
// ReSet GPIO16
//
GPIO_writePin(16, 0);

DELAY is defined as 

// Qualification period at 6 samples in microseconds
#define DELAY             (6.0 * 510.0 * 1000000.0 * (1.0 / DEVICE_SYSCLK_FREQ))

I calculate DELAY = 30.6.  This should lead to a delay of 30.6us.  However, when I observed the GPIO16 pin with the scope, I see 560ns of delay.  Please explain.  Thank you.  

DEVICE_SYSCLK_FREQ is defined as (in device.h)

//*****************************************************************************
//
// Defines related to clock configuration
//
//*****************************************************************************
//
// 20MHz XTAL on controlCARD and Launchpad. For use with SysCtl_getClock().
//
#define DEVICE_OSCSRC_FREQ             20000000U

//
// Define to pass to SysCtl_setClock(). Will configure the clock as follows:
// PLLSYSCLK = 20MHz (XTAL_OSC) * 10 (IMULT) * 1 (FMULT) / 2 (PLLCLK_BY_2)
//
#define DEVICE_SETCLOCK_CFG             (SYSCTL_OSCSRC_XTAL | SYSCTL_IMULT(10) | \
                                                                       SYSCTL_FMULT_NONE | SYSCTL_SYSDIV(2) | \
                                                                       SYSCTL_PLL_ENABLE)

//
// 100MHz SYSCLK frequency based on the above DEVICE_SETCLOCK_CFG. Update the
// code below if a different clock configuration is used!
//
#define DEVICE_SYSCLK_FREQ               ((DEVICE_OSCSRC_FREQ * 10 * 1) / 2)

//
// 25MHz LSPCLK frequency based on the above DEVICE_SYSCLK_FREQ and a default
// low speed peripheral clock divider of 4. Update the code below if a
// different LSPCLK divider is used!
//
#define DEVICE_LSPCLK_FREQ                 (DEVICE_SYSCLK_FREQ / 4)

 The DEVICE_DELAY_US()  macro is defined as (in device.h)

//*****************************************************************************
//
// Macro to call SysCtl_delay() to achieve a delay in microseconds. The macro
// will convert the desired delay in microseconds to the count value expected
// by the function. \b x is the number of microseconds to delay.
//
//*****************************************************************************
#define DEVICE_DELAY_US(x) SysCtl_delay(((((long double)(x)) / (1000000.0L / \
(long double)DEVICE_SYSCLK_FREQ)) - 9.0L) / 5.0L)