Interrupts occurrence

[Angelo Fraietta]

I have to make a correction on those previous calculations. I did not 
read the settings on my CRO correctly. The actual values are 1 message 
every 450 us, (not 4 us) and 1 every 500us.  So I am actually at the 
extremes. The maximum transfer I could expect from a MIDI device would 
be one byte every 320 us (10 bits per byte). So not setting the event 
(as Chris Johns suggested) does save me a valuable 50us.

Angelo Fraietta wrote:

> After some exhaustive testing I have come up with some figures that 
> represent data exchange rates between the Pic microcontroller and the 
> 386 using a PLA as an interface on an ISA bus using an interrupt 
> driven I/O read/write paradigm.
>
> What I have done is make the Pic and the 386 communicate with each 
> other, each triggering an interrupt with the other, causing it to 
> write to the other device.
>
> With the RTEMS event being triggered every  interrupt I have a 
> constant exchange rate of 1 message each way every 5 us.
>
> Triggering the event only if the receive queue is empty gives me an 
> exchange rate of 1 Message every 4 us. I am saving 1 us by not sending 
> the unnecessary event.
>
> The big factor in this test, however, is this method that I used to 
> check the exchange rates completely blows the 1 message every  650 us 
> measurement I previously made away, thus proving that the interrupt 
> rate will more than adequately sustain an input Midi stream running at 
> maximum transfer rate (31.25kbs, which is about 3 bytes per ms)
>
> Angelo Fraietta wrote:
>
>> You are right. Sending the event if the queue was not originally 
>> empty when the ISR came is not necessary. I was already looping the 
>> task until the queue was empty; I was, however, sending the event 
>> regardless -- which is actually wasting CPU cycles. Thanks for the 
>> tip? I'll see what I can get the interval down to by not sending an 
>> unnecessary event.
>>
>> Chris Johns wrote:
>>
>>>Angelo Fraietta wrote:
>>>
>>>>Within the ISR I am doing the following:
>>>>
>>>>Reading a 16 bit word from an I/O address
>>>>Decoding and adding that word onto a queue that is emptied out by a
>>>>running task
>>>>Checking a second queue for data that needs to be transmitted
>>>>Transmitting a word to the I/O card.
>>>>Setting an event that causes the running task to empty the queue.
>>>>
>>>
>>>I would only send the event if the queue is empty and have the task loop
>>>until the queue is empty.
>>> 
>>>
>>
>>-- 
>>Angelo Fraietta
>>
>>PO Box 859
>>Hamilton NSW 2303
>>
>>Home Page
>>
>>
>>http://www.users.bigpond.com/angelo_f/
>>
>>There are those who seek knowledge for the sake of knowledge - that is CURIOSITY
>>There are those who seek knowledge to be known by others - that is VANITY
>>There are those who seek knowledge in order to serve - that is LOVE
>>    Bernard of Clairvaux (1090 - 1153)
>>
>>
>
>-- 
>Angelo Fraietta
>
>PO Box 859
>Hamilton NSW 2303
>
>Home Page
>
>
>http://www.users.bigpond.com/angelo_f/
>
>There are those who seek knowledge for the sake of knowledge - that is CURIOSITY
>There are those who seek knowledge to be known by others - that is VANITY
>There are those who seek knowledge in order to serve - that is LOVE
>    Bernard of Clairvaux (1090 - 1153)
>
>

-- 
Angelo Fraietta

PO Box 859
Hamilton NSW 2303

Home Page


http://www.users.bigpond.com/angelo_f/

There are those who seek knowledge for the sake of knowledge - that is CURIOSITY
There are those who seek knowledge to be known by others - that is VANITY
There are those who seek knowledge in order to serve - that is LOVE
    Bernard of Clairvaux (1090 - 1153)


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