TMS320F28388D: Title: DEVICE_DELAY_US() Produces Longer Delay Than Expected on TMS320F28388D

Part Number: TMS320F28388D

Tool/software:

Title: DEVICE_DELAY_US() Produces Longer Delay Than Expected on TMS320F28388D

Description:

I'm working on the TMS320F28388D from the 2838x series. I'm observing that the DEVICE_DELAY_US() macro does not produce accurate delays.

Configuration:

• Device: TMS320F28388D

• Core: CPU1 (CPU2 is disabled)

• External Oscillator (XTAL): 25 MHz

  #define DEVICE_OSCSRC_FREQ 25000000U
  

• System Clock: 200 MHz

  #define DEVICE_SYSCLK_FREQ 200000000U
  

Issue:

When using the DEVICE_DELAY_US(x) macro:

#define DEVICE_DELAY_US(x) SysCtl_delay(((((long double)(x)) / (1000000.0L / \
                              (long double)DEVICE_SYSCLK_FREQ)) - 9.0L) / 5.0L)

I observe the following incorrect delays:

• DEVICE_DELAY_US(100) produces ~174 µs

• DEVICE_DELAY_US(1000000) (1 sec) produces ~1.57 seconds

This shows the delay is overestimated by ~57%.

Questions:

1. Is this macro definition incorrect for the setup above?

2. How should I correctly calculate the delay count for SysCtl_delay() at 200 MHz SYSCLK?

3. Could this be caused by wrong assumptions inside SysCtl_delay() (e.g., how many cycles per loop)?

   Thanks in advance for the support.