no-software internal RTC

[tzok]

Today I've discovered two things:
1) bit-mask for reading hour from ds3231 is 1 bit too short, and essentially unnecessary,
2) on TOS 1.62 it is not the CONTROL.ACC what polls the IKBD clock, but... STE_FIX.PRG (despite it is only for TOS 1.06, and here it displays that it is not required for this TOS).

[tzok]

Last update (hope so).

For TOS 1.x it requires STE_FIX to work, so it only works on STe with TOS 1.06 and 1.62. On TOS 2.06 it doesn't require any software, so it should work on any ST running this version of TOS.

Code after clean up:

Code: Select all

/******************************************************************
 Created with PROGRAMINO IDE for Arduino - 06.08.2018 15:23:03
 Project     : Atari ST IKBD clock injector with DS3231 RTC
 Libraries   : SoftwareSerial, Wire
 Author      : TzOk
 Description : ARD_RX0 from KB_5, ARD_TX1 to ST_5, ARD_D10 from/to KB/ST_6
******************************************************************/

#include <SoftwareSerial.h>
#include <Wire.h>

#define DS3231_ADDRESS (0x68)
#define DS3231_REG_TIME (0x00)

SoftwareSerial Ctrl(10, 11);

byte cmd;
byte inj = 255;
byte dsDate[7];
byte stDate[7] = {0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xFC};
//                ss,   mm,   hh,   DD,   MM,   YY

void setup()
{
  Serial.begin(7812);
  Ctrl.begin(7812);
  Ctrl.listen();
  Wire.begin();
}

void loop()
{
  if (Ctrl.available())
  {
    cmd = Ctrl.read();
    if (cmd == 0x1C) // Read RTC
    {
      Wire.beginTransmission(DS3231_ADDRESS);
      Wire.write(DS3231_REG_TIME);
      Wire.endTransmission();
      Wire.requestFrom(DS3231_ADDRESS, 7);
      while(!Wire.available()) {};
      for (byte i = 6; i < 255; i--)
      {
        dsDate[i] = Wire.read();
      }
      stDate[5] = (dsDate[1] & 0x80) ? dsDate[0] + 0xA0 : dsDate[0]; // YY : if CENTURY bit is SET => stDate = dsDate + 100
      stDate[4] = dsDate[1] & 0x1F; // MM
      stDate[3] = dsDate[2]; // DD
      stDate[2] = dsDate[4] & 0x3F; // hh
      stDate[1] = dsDate[5]; // mm
      stDate[0] = dsDate[6]; // ss
      inj = 6;
    }
    else if (cmd == 0x1B) // Set RTC
    {
      for (byte i = 5; i < 255; i--)
      {
        while(!Ctrl.available()) {};
        stDate[i] = Ctrl.read();
      }
      dsDate[0] = (stDate[5] < 0xA0) ? stDate[5] : stDate[5] - 0xA0; // YY : if stDate > 99 => dsDate = stDate - 100
      dsDate[1] = (stDate[5] < 0xA0) ? stDate[4] : stDate[4] + 0x80; // MM : if stDate > 99 => set CENTURY bit
      dsDate[2] = stDate[3]; // DD
      dsDate[3] = 0x01; // Day of Week : don't care, any valid value 1-7 will be ok`
      dsDate[4] = stDate[2]; // hh
      dsDate[5] = stDate[1]; // mm
      dsDate[6] = stDate[0]; // ss
      Wire.beginTransmission(DS3231_ADDRESS);
      Wire.write(DS3231_REG_TIME);
      for (byte i = 6; i < 255; i--)
      {
        Wire.write(dsDate[i]);
      }
      Wire.endTransmission();
    }
  }
}

void serialEvent() {
  if (inj == 255)
    Serial.write(Serial.read());
  else
  {
    Serial.read();
    Serial.write(stDate[inj--]);
  }
}

Explanation why it works - IKBD firmware has a "smart" BCD (de)coding routine, thus ignores any input that has a "halfbyte" value higher than 9, yet TOS has a "dumb" BCD (de)coding routine, which makes it accept any value. What is more, values like 0xA0 are correctly interpreted as 100. Atari programmers were obviously aware of this "feature", and that's why their control panel returns correct BCD values for years 80-99, and "erroneous" BCD for values 00-79* (as 100-179). In conjunction with the way the TOS internally stores the year it all works just fine, but not with the original IKBD.

* - actually I didn't check the year span which is sent as 20xx, and I'm not sure if the control.acc itself is responsible for setting the IKBD clock or, ste_fix.prg installs some clock update handler, to update the IKBD date when TOS date is changed. It is also interesting, why they have included IKBD<->TOS clock synchronization feature in ste_fix.prg, but not in TOS 1.62.

[tzok]

It is ready...

8165213200_1536065036-800x451.jpg (127.27 KiB) Viewed 1211 times

2757590500_1536065030-800x451.jpg (109.37 KiB) Viewed 1211 times

... and fits inside STe:

7399977500_1536065051-800x451.jpg (94.62 KiB) Viewed 1211 times

Edit by IngoQ: Images scaled and uploaded to forum, high-res pictures available here:

https://obrazki.elektroda.pl/8165213200_1536065036.jpg
https://obrazki.elektroda.pl/2757590500_1536065030.jpg
https://obrazki.elektroda.pl/7399977500_1536065051.jpg

[troed]

It is ready...
[images]

... and fits inside STe:
[images]

Will you be selling these yourself?

Edit by IngoQ: Removed images in quote

[tzok]

If there will be interest I may make a few units, but it was intended to be a DIY project. That is why I'm using a ready to use modules, rather than a custom PCB. It requires an Arduino Mini Pro or Nano V3 (or clone) and a "DS3231 for PI" RTC breakout board. Only very basic soldering skills are required for assembling such device.

[tzok]

I've done some further tests and:
* on STf(m) with TOS 1.00 - 1.04 it works using ST Control Panel (CONTROL.ACC), Panel is used both for synchronizing ST Clock with IKBD Clock on reboot and adjusting the clock,
* on STe with TOS 1.06/1.62 using STE_FIX.PRG and STE Control Panel (CONTROL.ACC), STE_FIX is used for synchronizing ST Clock with IKBD Clock on reboot, Panel is required only for adjusting the clock,
* on STe with TOS 2.06 it works using XControl (XCONTROL.ACC), ST Clock with IKBD Clock on reboot synchronization is done by TOS itself, Panel is required only for adjusting the clock.

[tzok]

I've experimentally measured the delay introduced by my ST IKBD RTC module:

SDS00048.png (164.6 KiB) Viewed 1136 times

dT = 1.28ms
For comparison - screen redraw time in color mode is 20ms.

[tzok]

One more notice - as the internal TOS date format is intact, any software using non-standard methods of reading it will still work correctly (however if using 2-digit year format we may see year 118 for 2018). As TOS stores a year on 7 bits it will work only until 2027.