[Coco] Drivewire question

[Boisy Pitre]

On Mar 25, 2009, at 9:01 PM, Willard Goosey wrote:

> On Wed, Mar 25, 2009 at 04:18:57PM -0700, Darren A wrote:
>> In the case of DriveWire, interrupts are not used for the serial data
>> transfers. All transactions are initiated at the request of the CoCo
>> and interrupts are masked during these transactions. Using the same
>> tecnique for a 6551 version of DriveWire would not require any
>> increase in bandwidth over the bus since the serial port  I/O is not
>> interleaved with I/O to any other device during a transaction.
>
> Does that also apply to the OS-9 client?  If so, wouldn't that rather
> hose multitasking?

Willard,


There is a slight impact, but there's an interesting trade off. The  
faster the data transmits, the less time interrupts stay masked, so at  
115,200bps, the typeahead buffer is very responsive.  Also to offset  
the loss of time due to masking of interrupts, the DriveWire 3 clock  
module asks the server for time at the top of every minute.

It's not perfect, but the compromises made make for quite a nice  
experience.

Boisy