[Coco] Another speed question

[Gene Heskett]

On Thursday 06 September 2007, Becker, Gary wrote:
>In a different thread, it was mentioned that the bit bang serial port
>and the hires mouse adapter takes too much CPU time. I understand why.
>Both devices use CPU timing loops and the interrupts have to be turned
>off. This discussion caused me to think about the way that I am doing
>the Serial Virtual Drive for the CoCo3FPGA under NitrOS-9. At the
>present time, I turn off interrupts and poll the serial port until I get
>the 256 byte sector. This takes approximately 25 mS. Since task
>switching happens every 16+ mS, I am guaranteed to miss at lease one
>interrupt. After the sector is received, I re-enable the interrupts. I
>do this because I am afraid that I cannot service interrupts from the
>serial port fast enough to keep up at 115200 bps. But I have never
>tried.
>
>It would take a major rewrite of the driver to make it interrupt driven.
>Is it worth the effort? Would it be better to lower the serial port /
>drive speed to keep interrupts enabled?
>
I don't believe this is possible due to where would one get the IRQ question?  
If edge triggered, how many bit spaces have elapsed since the last one?

One possibility that may or may not have been explored is that there may be a 
timer function in the gime, which could be programmed to fire an IRQ 
everytime a bit time has elapsed, minus of course the exec time of the 
service routine itself.  Or on a repeat basis but how would one go about 
achieving the initial bit synch unless the start bit coming in was a separate 
IRQ service routine to set that up, and then disable it till the stop bit 
comes in.

I haven't looked at that recently, so I have NDI if its granularity could be 
bent into a std rs232 timing stream.

>Gary
>
>
>
>
>--
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-- 
Cheers, Gene
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