IIC example

There doesn’t seem to be too many working examples in C accessing IIC devices from RISC OS.
The below example just gets the temperature from a DS3231 until escape is pressed.
Not sure if it’s the best way of doing it but it seems to work OK.

#include <stdio.h>
#include <time.h>
#include <stdint.h>
#include <assert.h>
#include "kernel.h"
#include "swis.h"

#define DS3231_I2C   0x68
#define I2C_RTC      DS3231_I2C

typedef struct iic_transfer {
  unsigned addr:8;
  unsigned :21;
  unsigned riscos_retry:1;
  unsigned checksumonly:1;
  unsigned nostart:1;
  union {
      unsigned checksum;
      void *data;
  } d;
  unsigned len;
} iic_transfer;

iic_transfer transfer[2] = {{0}};

uint8_t buffer1[1];
uint8_t buffer[2] = {0x0};

_kernel_oserror *err;
#define CONV 32

static inline int bcd_decimal(uint8_t hex)
{
    assert(((hex & 0xF0) >> 4) < 10);  // More significant nybble is valid
    assert((hex & 0x0F) < 10);         // Less significant nybble is valid
    int dec = ((hex & 0xF0) >> 4) * 10 + (hex & 0x0F);
    return dec;
}

static void delay(int number_of_seconds)
{
  int centi_seconds = 100 * number_of_seconds;
  clock_t start_time = clock();

  while (clock() < start_time + centi_seconds)
     ;

}

static uint8_t read_byte(uint8_t register_to_read)
{
  uint8_t buffer[1], buffer1[1];

  _kernel_swi_regs in, out;

  buffer1[0] = register_to_read; /* Read from register  */
  transfer[0].addr = I2C_RTC << 1; /* Write */
  transfer[0].d.data = buffer1;
  transfer[0].len=1;

  transfer[1].addr = (I2C_RTC << 1) | 1; /* Read */
  transfer[1].d.data = buffer;
  transfer[1].len=1;

  buffer[0]=0;
  in.r[0]=(int)&transfer; /* Pointer to list of iic_transfer structures */
  in.r[1]=2; /* Number of iic_tranfer structures */
  err=_kernel_swi(OS_IICOp, &in, &out);
  if (err != NULL) {
    printf("%s %x\n", err->errmess, err->errnum);
  }

  return buffer[0];
}

static void write_byte(uint8_t register_to_write, uint8_t value)
{

  uint8_t buffer[2], buffer1[1];

  _kernel_swi_regs in, out;

  buffer1[0] = register_to_write; /* Write to register */
  transfer[1].addr = (I2C_RTC << 1); /* Write */
  transfer[1].d.data = buffer1;
  transfer[1].len=1;
  
  buffer[0] = register_to_write; /* Write to register */
  buffer[1] = value; /* Value to Write */
  transfer[1].addr = (I2C_RTC << 1); /* Write */
  transfer[1].d.data = buffer;
  transfer[1].len=2;

  in.r[0]=(int)&transfer; /* Pointer to list of iic_transfer structures */
  in.r[1]=2; /* Number of iic_tranfer structures */
  err=_kernel_swi(OS_IICOp, &in, &out);
  if (err != NULL) {
    printf("%s %x\n", err->errmess, err->errnum);
  }

}

static void conv_temp(void)
{
  uint8_t byte_control;

  byte_control = read_byte(0x0e);

  /* The 'Convert Temperature' 'Control Register' needs to be set for a user
   * initiated temperature conversion.
   */  
  if ((byte_control & CONV) == 0)
     write_byte(0x0e, byte_control|CONV);

  byte_control = read_byte(0x0e);

  /* Wait for the temperature conversion to be finished */
  while ((byte_control & CONV) != 0) {

     delay(1);
     byte_control = read_byte(0x0e);

  }

}

int main(void) {

  _kernel_swi_regs in, out;
  int temp1, temp2;

  while(1) {
  
     conv_temp();
 
     buffer1[0] = 0x11; /* Read from register onwards - starts at zero */
     transfer[0].addr = I2C_RTC << 1; /* Write */
     transfer[0].d.data = buffer1;
     transfer[0].len=1;

     transfer[1].addr = (I2C_RTC << 1) | 1; /* Read */
     transfer[1].d.data = buffer;
     transfer[1].len=2;

     buffer[0]=0;
     buffer[1]=0;
     in.r[0]=(int)&transfer; /* Pointer to list of iic_transfer structures */
     in.r[1]=2; /* Number of iic_tranfer structures */
     err=_kernel_swi(OS_IICOp, &in, &out);
     if (err != NULL) {
        printf("%s %x\n", err->errmess, err->errnum);
     }
     
     temp1=buffer[0]&0x7f;
     temp2=((buffer[1]&0xc0)>>6)*25;
     printf("temperature: %d.%d C\n", temp1, temp2);

  }

}

Well, if it works then there’s nothing to worry about. ;-)

OMG, that’s dirt cheap. Can RISC OS use the RTC and/or NVRAM?

Can RISC OS use the RTC and/or NVRAM?

The RTC gets used automatically by RISC OS. Not looked at the NVRAM. I think there’s only 32 bytes.

> The RTC gets used automatically by RISC OS

In RPCEmu, direct also works. For real RTC connected to a Pi – should work similar:

  unsigned char buffer[] = {0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
  int cnt = 0;

  while (1)
  {
    // RTC PCF8583 address 0x50 + write : register address 0x00
    buffer[0] = 0x00;
    IIC_Control((0x50 << 1) + 0, (int) buffer, 1);

    // RTC PCF8583 address 0x50 + read  : 8 bytes auto-increment
    IIC_Control((0x50 << 1) + 1, (int) buffer, 8);

    printf("%d\n", cnt);
    printf("status   = 0x%02x\n", buffer[0]);
    printf("centisec = 0x%02x\n", buffer[1]);
    printf("sec      = 0x%02x\n", buffer[2]);
    printf("min      = 0x%02x\n", buffer[3]);
    printf("hour     = 0x%02x\n", buffer[4]);
    printf("year     = 0x%02x\n", buffer[5]);
    printf("month    = 0x%02x\n", buffer[6]);
    printf("timer    = 0x%02x\n", buffer[7]);
    printf("\n");

    cnt++;
    delay(50);
  }

If the NVRAM device is a 24C32 as shown in the photo, it’s a 4k*8 serial EEPROM.

If the NVRAM device is a 24C32 as shown in the photo, it’s a 4k*8 serial EEPROM.

I think the 24C32 is an obsolete device, the replacement is the 24LC32A.
Cheaper than chips¹ – 26.3p at Farnell
Weird price – even with VAT the unit price still has fractions of a penny.

¹ Which, having risen in price over the years (up with potato prices and never back down with them) aren’t actually that cheap. No, chips are NOT “fries”², which are a mistake on many levels.

I think the 24C32 is an obsolete device, the replacement is the 24LC32A.

They still can be had! Octopart is your friend.

Cheaper than chips – 26.3p at Farnell
Weird price – even with VAT the unit price still has fractions of a penny.

Some parts we buy have prices in pence with two or three decimal places. They expect people to be ordering in 100’s or more using rounding if necessary.

They still can be had! Octopart is your friend.

Two things:
Octopart are spares rather than new designs, even they point to the new
The L in the LC has a significance which is useful in an application like this.

Some parts we buy have prices in pence with two or three decimal places. They expect people to be ordering in 100’s or more using rounding if necessary.

When you buy in 100’s it’s a different fraction…