On 14 Jun 2012, at 05:12, Graham Cox wrote:
On 14/06/2012, at 8:03 AM, Dave wrote:
In assembler this would be implemented is using an "Exchange
Instruction" to alter the PC on the stack and cause it to return
to the correct place once the ASync Task (usually an interrupt)
had finished.
Ah, those were the days - push a calculated address on the stack
and do a 'RET' to cause a jump to that address... thankfully such
tricks are wholly unnecessary these days. In fact a simple
switch...case statement does the same job in most cases.
I'm not sure of the answer to your question though, seems to me you
could simply queue each task then the next executes as soon as the
one ahead of it finishes.
The point is you can't queue B until the data from A has been
obtained and that might take a long while. There are two ways to deal
with it, either have a call back from the lower level that returns
the data (in which case you have to specify an address/selector to go
to when the data has been obtained sucessfully), OR you can invert
the control and make the interface look as it is demand based, even
though the data is being obtained as and when it is ready.
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