Re: Android Headset specification

On Thu, Jan 24, 2019 at 10:36:08AM +0100, Mia Magnusson wrote:
>>But I don't think that it could be faster than the 38,400bps that 
>>c2nload achieves with its custom protocol.
>
>What limits it to 38400? Is that due to that there being no selectable 
>frequency between 38400 and 115200 on a PC, the Commodore is too slow 
>for 115200 and the C2N232 is intended to work with the standard speeds
>of a PC? If so it might be a good idea to try using an Amiga or 
>anything else which can do more variable baud rates?

For c2nload, the limit is the processing speed on a PAL C64, I think 
with the screen enabled. Before I found a tweak to the code, I was 
unable to get a reliable transfer. My transfer routine does bank 
switching, so it can write to any RAM location, including $d000-$dfff 
where the CIA is mapped.

On Linux, it seemed to me that a write() call cannot really be 
interrupted; neither XON/XOFF nor CTS/RTS flow control seemed to have 
any effect on it. It would be written in multiples of 4096 bytes even if 
you killed the process. So, I tried to ensure that the Commodore side is 
fast enough so that the 124-byte buffer in the AT90S2313 or ATtiny2313 
never fills up.

>But if it anyway should have a microprocessor and connect to the
>cassette port, it might be able to use some of the pins in some
>unusual way. We have already seen that CASS_WRITE is connected to a
>standard port of one of the VIAs in a VIC 20, so that could be used
>both as an input and an output. The same is true for CASS_SENSE on the
>VIC 20. Any first-stage loader should be able to detect which
>Commodore model it's running on and adapt to the hardware capabilities.

Yes, that would be a possibility. If I remember correctly, the 264 
series had something strange about the signals, compared to the others.  
Maybe it was that the CASS READ signal is connected to a GPIO pin, and 
not to the FLAG input of the VIA or CIA that is only able to detect 
falling edges. Also the tape format is radically different on the 264 
series (slower if my memory serves).

	Marko