TMS320F28035: Cputimer0

Now i use CCS to connect to a DRV8312 EVM board. I configure CPU timer2, and give PRD to 299.

void InitDRVSysBCPUTimer2(void)
{
// Initialize internal variables used in this function

// Step 3.5 Interrupts that are used in DRV system are re-madpped to
// ISR functions found in each module
EALLOW; // This is needed to write to EALLOW protected register
PieVectTable.TINT2 = &cpu_timer2_isr;
EDIS; // This is needed to disable write to EALLOW protected registers

// Step 4. Initialize all the Device Peripherals:
// DRVInitCpuTimers(); // For this example, only initialize the Cpu Timers
// Initialize timer period to maximum:
CpuTimer2Regs.PRD.all = 0xFFFFFFFF;
// Initialize pre-scale counter to divide by 1 (SYSCLKOUT):
CpuTimer2Regs.TPR.all = 0;
CpuTimer2Regs.TPRH.all = 0;
// Make sure timer is stopped:
CpuTimer2Regs.TCR.bit.TSS = 1;
// Reload all counter register with period value:
CpuTimer2Regs.TCR.bit.TRB = 1;
// Reset interrupt counters:
CpuTimer2.InterruptCount = 0;
// Configure CPU-Timer 0 to interrupt every 5 us:
//60MHz CPU Freq, 5 us Period (in uSeconds)
// DRVConfigCpuTimer(&CpuTimer0, 120, 5);

CpuTimer2Regs.PRD.all = 100;// Counter decrements PRD+1 times each period

// Set pre-scale counter to divide by 1 (SYSCLKOUT):
CpuTimer2Regs.TPR.all = 0;
CpuTimer2Regs.TPRH.all = 0;

// Initialize timer control register:
CpuTimer2Regs.TCR.bit.TSS = 1; // 1 = Stop timer, 0 = Start/Restart Timer
CpuTimer2Regs.TCR.bit.TRB = 1; // 1 = reload timer
CpuTimer2Regs.TCR.bit.SOFT= 0;
CpuTimer2Regs.TCR.bit.FREE= 0; // Timer Free Run Enabled
CpuTimer2Regs.TCR.bit.TIE =1; // 0 = Disable/ 1 = Enable Timer Interrupt

// Reset interrupt counter:
CpuTimer2.InterruptCount = 0;

// Step 5. Initialize user variables in each module

// Step 6. Configure registers in each module:

// Step 7. Enable interrupts in PIE for each module:
// Do not need to configure PIE for cputimer1
IER |= M_INT14; // Enable CPU Interrupt 2
// Step 8. Wait for each interrupts in each module;

}

I configure PLL as

#define DSP28_PLLCR 12 // 60 MHz devices [60 MHz = (10MHz * 12)/2]
#define DSP28_DIVSEL 2 // Enable /2 for SYSCLKOUT

I create a cpu timer 2 interrupt and
__interrupt void cpu_timer2_isr(void)
{

CpuTimer1.InterruptCount++;
TOGGLEGPIOFlag();
CpuTimer2Regs.TCR.bit.TIF = 1; /* Clear interrupt flag (TIF) for CPU timer2 */

}

In TOGGLEGPIOFlag() function, i toggle GPIO22

void TOGGLEGPIOFlag(void)
{
EALLOW;
GpioCtrlRegs.GPAPUD.bit.GPIO22 = 0; // Enable internal pull up resistor on GPIO22 (Default is disable)
GpioDataRegs.GPATOGGLE.bit.GPIO22 = 1; // Toggle output
GpioCtrlRegs.GPAMUX2.bit.GPIO22 = 0; // Configure GPIO22 as general input and output (default)
GpioCtrlRegs.GPADIR.bit.GPIO22 = 1; // Configure GPIO22 as output
EDIS;
}

In this case, i should have 5 us period, but i only have 6.4 us.a

I try to configure PRD to 100, and period is also 6.4 us. I try to configure PRD to 600, and period is 10 us. That means if I want period is more than 6.4 us, it is ok. But if I want period is less than 6.4 us, it is not ok.

Then, I try to a example in Control suite. Example_2803xCpuTimer. When I configure CPU timer2 to more than 4 us, it is ok. But if I configure CPU timer2 to 1, it can only output 4 us.

//###########################################################################
// Description:
//! \addtogroup f2803x_example_list
//! <h1>Cpu Timer (cpu_timer)</h1>
//!
//! This example configures CPU Timer0, 1, and 2 and increments
//! a counter each time the timer asserts an interrupt.
//!
//! \b Watch \b Variables \n
//! - CpuTimer0.InterruptCount
//! - CpuTimer1.InterruptCount
//! - CpuTimer2.InterruptCount
//
//###########################################################################
// $TI Release: F2803x C/C++ Header Files and Peripheral Examples V130 $
// $Release Date: May 8, 2015 $
// $Copyright: Copyright (C) 2009-2015 Texas Instruments Incorporated -
// http://www.ti.com/ ALL RIGHTS RESERVED $
//###########################################################################

#include "DSP28x_Project.h" // Device Headerfile and Examples Include File

// Prototype statements for functions found within this file.
__interrupt void cpu_timer0_isr(void);
__interrupt void cpu_timer1_isr(void);
__interrupt void cpu_timer2_isr(void);

void main(void)
{
// Step 1. Initialize System Control:
// PLL, WatchDog, enable Peripheral Clocks
// This example function is found in the DSP2803x_SysCtrl.c file.
InitSysCtrl();

// Step 2. Initialize GPIO:
// This example function is found in the DSP2803x_Gpio.c file and
// illustrates how to set the GPIO to it's default state.
// InitGpio(); // Skipped for this example

// Step 3. Clear all interrupts and initialize PIE vector table:
// Disable CPU interrupts
DINT;

// Initialize the PIE control registers to their default state.
// The default state is all PIE interrupts disabled and flags
// are cleared.
// This function is found in the DSP2803x_PieCtrl.c file.
InitPieCtrl();

// Disable CPU interrupts and clear all CPU interrupt flags:
IER = 0x0000;
IFR = 0x0000;

// Initialize the PIE vector table with pointers to the shell Interrupt
// Service Routines (ISR).
// This will populate the entire table, even if the interrupt
// is not used in this example. This is useful for debug purposes.
// The shell ISR routines are found in DSP2803x_DefaultIsr.c.
// This function is found in DSP2803x_PieVect.c.
InitPieVectTable();

// Interrupts that are used in this example are re-mapped to
// ISR functions found within this file.
EALLOW; // This is needed to write to EALLOW protected registers
PieVectTable.TINT0 = &cpu_timer0_isr;
PieVectTable.TINT1 = &cpu_timer1_isr;
PieVectTable.TINT2 = &cpu_timer2_isr;
EDIS; // This is needed to disable write to EALLOW protected registers

// Step 4. Initialize the Device Peripheral. This function can be
// found in DSP2803x_CpuTimers.c
InitCpuTimers(); // For this example, only initialize the Cpu Timers

// Configure CPU-Timer 0, 1, and 2 to interrupt every second:
// 60MHz CPU Freq, 1 second Period (in uSeconds)

ConfigCpuTimer(&CpuTimer0, 60, 1000000);
ConfigCpuTimer(&CpuTimer1, 60, 1000000);
ConfigCpuTimer(&CpuTimer2, 60, 1);

// To ensure precise timing, use write-only instructions to write to the entire register. Therefore, if any
// of the configuration bits are changed in ConfigCpuTimer and InitCpuTimers (in DSP2803x_CpuTimers.h), the
// below settings must also be updated.

CpuTimer0Regs.TCR.all = 0x4000; // Use write-only instruction to set TSS bit = 0
CpuTimer1Regs.TCR.all = 0x4000; // Use write-only instruction to set TSS bit = 0
CpuTimer2Regs.TCR.all = 0x4000; // Use write-only instruction to set TSS bit = 0

// Step 5. User specific code, enable interrupts:

// Enable CPU int1 which is connected to CPU-Timer 0, CPU int13
// which is connected to CPU-Timer 1, and CPU int 14, which is connected
// to CPU-Timer 2:
IER |= M_INT1;
IER |= M_INT13;
IER |= M_INT14;

// Enable TINT0 in the PIE: Group 1 interrupt 7
PieCtrlRegs.PIEIER1.bit.INTx7 = 1;

// Enable global Interrupts and higher priority real-time debug events:
EINT; // Enable Global interrupt INTM
ERTM; // Enable Global realtime interrupt DBGM

// Step 6. IDLE loop. Just sit and loop forever (optional):
for(;;);
}

__interrupt void cpu_timer0_isr(void)
{
CpuTimer0.InterruptCount++;

// Acknowledge this interrupt to receive more interrupts from group 1
PieCtrlRegs.PIEACK.all = PIEACK_GROUP1;
}

__interrupt void cpu_timer1_isr(void)
{
CpuTimer1.InterruptCount++;
// The CPU acknowledges the interrupt.
EDIS;
}

__interrupt void cpu_timer2_isr(void)
{
EALLOW;
CpuTimer2.InterruptCount++;
// The CPU acknowledges the interrupt.

EALLOW;
GpioCtrlRegs.GPAPUD.bit.GPIO22 = 0; // Enable internal pull up resistor on GPIO22 (Default is disable)
GpioDataRegs.GPATOGGLE.bit.GPIO22 = 1; // Toggle output
GpioCtrlRegs.GPAMUX2.bit.GPIO22 = 0; // Configure GPIO22 as general input and output (default)
GpioCtrlRegs.GPADIR.bit.GPIO22 = 1; // Configure GPIO22 as output
EDIS;
}

//===========================================================================
// No more.
//===========================================================================

1. I use GPIO18 as XCLKOUT and configure XCLKOUTDIV as 2 (System Clock). I test GPIO18 with oscilloscope. And it is 60MHz. That means there is no problem for system clock.

2. I only toggle GPIO and clear cpu timer interrupt flag in the cpu timer interrupt. It can not more than 5 us.

I want to know what is this problem and what is the mininal value, CPU timer can output.

Thanks very much