[Coco] DW and 6551

[Joe Grubbs]

That makes sense... The faster your tx/rx speed, the buffer has to grow as well to be effective. So realistically, it's possible that using an old 6551 with high speed will have a small or perhaps insignificant impact on CPU load reduction versus the bit banger. Bummer.




> Date: Wed, 11 Feb 2015 15:17:21 +0000
> From: mmarlette at frontiernet.net
> To: coco at maltedmedia.com
> Subject: Re: [Coco] DW and 6551
> 
> Joe,
> 
> The real question in my mind is the effective baud rate. The 6551 has a one or two byte buffer. Back in the 300 baud days, that was ok.
> 
> 
> Today the Wiznet chips have 16k-128K TX/RX buffers. Not all transactions of course require that amount of buffer space but you can see that there are a lot of system calls to service the data stream which cuts your baud rate down. So even if you are running at 115.2k baud the effective rate is much less do to the system overhead to service the data stream, thus putting a high burden on the CPU.
> 
> Just to handle the response query from a server to indicate your current IP is ~265 bytes. Not a big deal, but considering all you are trying to find out is a string with a max length of 15, you can see the additional overhead.
> 
> 
> Throw in no flow control and it is a recipe for a disaster, IMHO.
> 
> I haven't done it yet and don't think it is a big deal to do but I will have a 6551 emulator in the Xmega on my USB COM port. Tying the CPLD, Xmega and the USB all together to think it is a 6551 running over a megabaud with flow control and huge buffers.
> 
> Regards,
>  
> Mark Marlette 
> http://www.cloud9tech.com 
> mark at cloud9tech.com 
> ________________________________
> From: Joe Grubbs <jsgrubbs at hotmail.com>
> To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com> 
> Sent: Wednesday, February 11, 2015 8:52 AM
> Subject: Re: [Coco] DW and 6551
> 
> 
> Just now catching up with the thread.
> 
> So from the way it sounds, the 6551 is probably reliable enough as long as I'm not hammering it with multiple telnet sessions and/or extremely high speed?
> 
> The whole reason I was entertaining the idea was to give the CPU a bit of a breather, but also to free up the bit-banger port for a native connection to one of my printers. Seems silly I know since the only things I print are the occasional IMAX movie tickets and coupons for Smoothie King--both of which I do from my ink jet anyway :P
> 
> If there's going to be a new and improved RS232 Pak, count me in!
> 
> 
> 
> 
> 
>                           
> 
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