How to use the GPT12 Incremental Encoder Driver

Collaboration diagram for How to use the GPT12 Incremental Encoder Driver:

The IncrEnc interface can be used in one of the following configurations T3 as core or T2 as core

Setup with T3 as core

• T3 as incremental mode
  • Multiplication factor:
    • twoFold: use both edges of TxIn
    • fourFold: use both edges of TxIn and TxEUD
    • Reverse of direction supported by GPT12
    • T3 value diff is used for speed calculation at high speed (speed > speedModeThreshold)
• T4 used for zero signal detection if pinZ is not NULL
  • interrupt is generated to support turn calculation if zeroIsrPriority != 0
  • T4 clears T3 on zero signal event on TxIn input
• T5 used for low speed calculation (speed < speedModeThreshold)
  • Rising edge of TxIn or TxEUD captures the T5 timer in CAPREL

Setup with T2 as core

• T2 as incremental mode
  • Multiplication factor:
    • twoFold: sample on both edges of TxIn
    • fourFold: sample on both edges of TxIn and TxEUD
    • Reverse of direction supported by GPT12
    • T2 value diff is used for speed calculation at high speed
• T4 used for zero signal detection if pinZeroTxEUD is not NULL
• T4 clears T2 on zero signal event on TxEUD input

Preparation

Include Files

Include following header file into your C code:

#include <Gpt12/Gpt/IfxGpt12_IncrEnc.h>

Variables

// used globally
static IfxGpt12_IncrEnc gpt12;

Interrupt Handler Installation

See also How to define Interrupts?

Define priorities for the Interrrupt handlers. This is normally done in the Ifx_IntPrioDef.h file:

// priorities are normally defined in Ifx_IntPrioDef.h
#define ISR_PRIORITY_INCRENC_ZERO 6

Add the interrupt service routines to your C code. They have to call the GPT12 interrupt handlers by passing the gpt12 handle:

IFX_INTERRUPT(ISR_IncrIncZero, 0, ISR_PRIORITY_INCRENC_ZERO)
{
    IfxGpt12_IncrEnc_onZeroIrq(&gpt12);
}

Finally install the interrupt handlers in your initialisation function:

// install interrupt handlers
IfxCpu_Irq_installInterruptHandler(&ISR_IncrIncZero, ISR_PRIORITY_INCRENC_ZERO);
IfxCpu_enableInterrupts();

Module Initialisation

The module initialisation can be done in the same function. Here an example:

// Initialize global clocks
IfxGpt12_enableModule(&MODULE_GPT120);
IfxGpt12_setGpt1BlockPrescaler(&MODULE_GPT120, IfxGpt12_Gpt1BlockPrescaler_8);
IfxGpt12_setGpt2BlockPrescaler(&MODULE_GPT120, IfxGpt12_Gpt2BlockPrescaler_4);

// create module config
IfxGpt12_IncrEnc_Config gpt12Config;
IfxGpt12_IncrEnc_initConfig(&gpt12Config , &MODULE_GPT120);

// implementation with T3 as core
gpt12Config.base.offset                    = 0;
gpt12Config.base.reversed                  = FALSE;
gpt12Config.base.resolution                = 2048;
gpt12Config.base.periodPerRotation         = 1;
gpt12Config.base.resolutionFactor          = IfxStdIf_Pos_ResolutionFactor_fourFold;
gpt12Config.base.updatePeriod              = 100e-6;
gpt12Config.base.speedModeThreshold        = 200;
gpt12Config.base.minSpeed                  = 10;
gpt12Config.base.maxSpeed                  = 500;
gpt12Config.zeroIsrPriority                = ISR_PRIORITY(INTERRUPT_INCRINC_ZERO);
gpt12Config.zeroIsrProvider                = ISR_PROVIDER(INTERRUPT_INCRINC_ZERO);
gpt12Config.pinA                           = &IfxGpt120_T3INA_P02_6_IN;
gpt12Config.pinB                           = &IfxGpt120_T3EUDA_P02_7_IN;
gpt12Config.pinZ                           = &IfxGpt120_T4INA_P02_8_IN;
gpt12Config.pinMode                        = IfxPort_InputMode_noPullDevice;

gpt12Config.base.speedFilterEnabled        = TRUE;
gpt12Config.base.speedFilerCutOffFrequency = config.base.maxSpeed / 2 * IFX_PI * 2;


// initialize module
//IfxGpt12_IncrEnc gpt12; // defined globally
IfxGpt12_IncrEnc_init(&gpt12, &gpt12Config);

Update

speed, position and direction of the incremental encoder can be collected by the following

float32 speed, rawPosition;
IfxStdIf_Pos_Dir direction;

Ifx_TickTime tickRefresh     = gpt12.updatePeriod * TimeConst_1s;

Ifx_TickTime refreshDeadLine = now();

if (isDeadLine(refreshDeadLine))
{
    refreshDeadLine = addTTime(refreshDeadLine, tickRefresh);
    IfxGpt12_IncrEnc_update(&gpt12);

    speed       = IfxGpt12_IncrEnc_getSpeed(&gpt12);
    rawPosition = IfxGpt12_IncrEnc_getRawPosition(&gpt12);
    direction   = IfxGpt12_IncrEnc_getDirection(&gpt12);
}