AMT22.c

/*
  AMT22.c - STM32 library for ATM22 series absolute encoders by CUI Devices.
  Created by Simone Di Blasi, December 2020.
*/

#include "AMT22.h"

/* SPI commands */
#define AMT22_NOP       0x00
#define AMT22_RESET     0x60
#define AMT22_ZERO      0x70

#define RES12           12
#define RES14           14


void setCSLine (GPIO_TypeDef* encoderPort, uint16_t encoderPin, GPIO_PinState csLine)
{
	HAL_GPIO_WritePin(encoderPort, encoderPin, csLine);
}

uint8_t spiWriteRead(SPI_HandleTypeDef *hspi, uint8_t sendByte, GPIO_TypeDef* encoderPort, uint16_t encoderPin, uint8_t releaseLine, TIM_HandleTypeDef *timer)
{
  //to hold received data  
  uint8_t data;

  //set cs low, cs may already be low but there's no issue calling it again except for extra time
  setCSLine(encoderPort, encoderPin , GPIO_PIN_RESET);

  //There is a minimum time requirement after CS goes low before data can be clocked out of the encoder.
  delay(timer, 3);
  //send the command and receive response of the slave
  HAL_SPI_TransmitReceive(hspi, &sendByte, &data, 1, 10);

  //There is also a minimum time after clocking that CS should remain asserted before we release it
  delay(timer, 3);
  setCSLine(encoderPort, encoderPin, releaseLine); //if releaseLine is high set it high else it stays low

  return data;
}

uint16_t getPositionSPI(SPI_HandleTypeDef *hspi, GPIO_TypeDef* encoderPort, uint16_t encoderPin, uint8_t resolution, TIM_HandleTypeDef *timer)
{
  uint16_t currentPosition;       //16-bit response from encoder
  uint8_t binaryArray[16];        //after receiving the position we will populate this array and use it for calculating the checksum

  //get first byte which is the high byte, shift it 8 bits. don't release line for the first byte
  currentPosition = spiWriteRead(hspi, AMT22_NOP, encoderPort, encoderPin, 0, timer) << 8;

  //this is the time required between bytes as specified in the datasheet.
  delay(timer, 3);

  //OR the low byte with the currentPosition variable. release line after second byte
  currentPosition |= spiWriteRead(hspi, AMT22_NOP, encoderPort, encoderPin, 1, timer);

  //run through the 16 bits of position and put each bit into a slot in the array so we can do the checksum calculation
  for(int i = 0; i < 16; i++) binaryArray[i] = (0x01) & (currentPosition >> (i));

  //using the equation on the datasheet we can calculate the checksums and then make sure they match what the encoder sent
  if ((binaryArray[15] == !(binaryArray[13] ^ binaryArray[11] ^ binaryArray[9] ^ binaryArray[7] ^ binaryArray[5] ^ binaryArray[3] ^ binaryArray[1]))
          && (binaryArray[14] == !(binaryArray[12] ^ binaryArray[10] ^ binaryArray[8] ^ binaryArray[6] ^ binaryArray[4] ^ binaryArray[2] ^ binaryArray[0])))
    {
      //we got back a good position, so just mask away the checkbits
      currentPosition &= 0x3FFF;
    }
  else
  {
    currentPosition = 0xFFFF; //bad position
  }

  //If the resolution is 12-bits, and wasn't 0xFFFF, then shift position, otherwise do nothing
  if ((resolution == RES12) && (currentPosition != 0xFFFF)) currentPosition = currentPosition >> 2;
  return currentPosition;
}

void setZeroSPI(SPI_HandleTypeDef *hspi, GPIO_TypeDef* encoderPort, uint16_t encoderPin, TIM_HandleTypeDef *timer)
{
  spiWriteRead(&hspi,AMT22_NOP, encoderPort, encoderPin, 0, timer);

  //There is also a minimum time after clocking that CS should remain asserted before we release it
  delay(timer, 3);

  spiWriteRead(&hspi, AMT22_ZERO, encoderPort, encoderPin, 1, timer);


  delay(timer, 250);
}

void resetAMT22(SPI_HandleTypeDef *hspi, GPIO_TypeDef* encoderPort, uint16_t encoderPin, TIM_HandleTypeDef *timer)
{
  spiWriteRead(&hspi, AMT22_NOP, encoderPort, encoderPin, 0, timer);

  //There is also a minimum time after clocking that CS should remain asserted before we release it
  delay(timer, 3);

  spiWriteRead(&hspi, AMT22_RESET, encoderPort, encoderPin, 1, timer);

  delay(timer, 250);
}

void delay(TIM_HandleTypeDef *timer, uint32_t delayTime){
	uint32_t startTime = __HAL_TIM_GET_COUNTER(timer); 	//reference point to count passed time
	uint32_t passedTime  = 0;

	while (passedTime<delayTime){
		passedTime = __HAL_TIM_GET_COUNTER(timer) - startTime;
		if (passedTime<0){
			passedTime +=timer->Init.Period;
		}
	}
}