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Best practices for sensing disks and content, creating multi-disk software?


28 replies to this topic

#26 Nezgar OFFLINE  

Nezgar

    Dragonstomper

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  • Location:Regina SK Canada

Posted Sat Feb 17, 2018 4:03 AM

 The byte rate that determines the audible pitch is independent of the bit rate, which is why loading from a 1050 sounds noticeably lower in pitch than from an 810.

 

Why is the byte rate lower on the 1050? Are you saying the bit rate is the same as a Stock 810? I've noticed the tone is lower on 1050 vs 810. 1050 US Doubler & Happy make it sound the same as 810 in standard speed SIO though...



#27 phaeron OFFLINE  

phaeron

    River Patroller

  • 2,481 posts
  • Location:USA

Posted Sat Feb 17, 2018 11:04 PM

 

Why is the byte rate lower on the 1050? Are you saying the bit rate is the same as a Stock 810? I've noticed the tone is lower on 1050 vs 810. 1050 US Doubler & Happy make it sound the same as 810 in standard speed SIO though...

 

Bit rate is faster on the 1050, actually. Stock 810 sends at 26 cycles/bit (19230 baud) and 265 cycles/byte (1887 bytes/sec) at 500KHz, while 1050 sends at 51 cycles/bit (19608 baud) and 549 cycles/byte (1822 bytes/sec) at 1MHz. Both the 810 and the 1050 bit-bang the serial bus on the 6507/6502, so the bit and byte rates are completely up to the firmware. Only the Atari of three decades ago would know why the 1050 uses the rate that it does; the alternate firmwares for the 1050 prove that more accurate or 810-faithful rates are possible. The US Doubler's byte rate is indeed closer to the 810: 534 cycles/byte (1873 bytes/sec).

 

The bit rate is the critical rate for transfer reliability since the sender and receiver only sync on each start bit; the difference between the sender and receiver clocks then determines how much skew accumulates during the byte. This is the reason for the 5% rate error spec in the POKEY documentation -- that's the point at which the sender and receiver get out of sync by one-half bit. The byte rate, on the other hand, affects the pitch you hear and the total duration of the transfer (which can in turn affect copy protection timing).



#28 Nezgar OFFLINE  

Nezgar

    Dragonstomper

  • 748 posts
  • Location:Regina SK Canada

Posted Mon Feb 19, 2018 1:48 AM

Thanks for the detailed explanation, phaeron, one of my longtime mysteries answered! This would also explain why the pitch when using particular POKEY divisors on SIO2PC for instance don't seem to match up to the sound of real devices - IE, Speedy 0x9 and Happy/USD 0xA.



#29 Mclaneinc OFFLINE  

Mclaneinc

    Quadrunner

  • 5,616 posts
  • Location:Northolt, UK

Posted Mon Feb 19, 2018 4:28 AM

We wonder if we are alone in the Universe, well I can confirm we are not, Phaeron proves it, no one can know so much and be human :)

 

Just don't take all our bases!!

 

Seriously, I love these threads, I am stone age man compared to you guys but I understand some of this but what is so special is that after all this time the level of detailed 'how it works' is out there for others to benefit from.

 

Hats off to all involved...

 

OT interruption over, back to work guys :)

 

Paul..






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