DT-Ints latency and other interrupt conciderations

[Ioannis]

Ioannis,
It'll have to be some kind of interrupt driven buffer routine for both sending and receiving, I think. I'd like to be able to send the current error while the system is running so the following error can be watched in "real time".

I'm currently looking at Microchips AN744 which seems to do pretty much what I need. "All" I have to do is figure out how it works and what I need to do get it working "in" PBP.

/Henrik.

Checking the RCIF/TXIF or RC1IF/TX1IF (for the 18Fseries) flags I think is enough to see if the UART is ready to send or has received a byte.

Of course the checks and byte read/write to the UART are not free and need your precious time each.

Maybe you have to move to a higher grade PIC like the 24F or even on the 32bit ones but then you also have to say good bye to PBP.

Ioannis

[HenrikOlsson]

Ioannis,
Nah, it should be doable with the 18F series - I'm almost there now. Like I said earlier I have a comercially available drive that is based on the 18F2431 and it works fine, step-rate specified to 400kHz (not verified) and USB interface thru some FTDI-chip.

I've got the code from AN744 working "inside" a very simple PBP program - 5 lines of PBP code and 200 lines of ASM. Now I only need to figure out HOW it works so I get it to do what I need. I may opt for interrupt driven RX and polled TX though.

Anyway, I think I'll start a separate thread for that...

Thanks!
/Henrik.

[Ioannis]

The AN I think is 774 not 744. The driver you have might be based on pure assembly. What clock does it have?

Ioannis

[HenrikOlsson]

Of course, you're right! I've mentioned it twice now and managed to get it wrong both times.

Obviously I don't have access to the source code for the drive but I was told by the developer that he was using MPLAB+BOOSTC (that probably means ASM for the time critical stuff and C for the rest). I don't know what oscillator speed it uses but I suspect it's 10*4MHz.

/Henrik.

[Ioannis]

It makes sense to be so. Are you clocking at this speed too?

Ioannis

[HenrikOlsson]

The protoype, on which I managed to get 60kHz+ yesterday, is still running on 20Mhz which makes me believe I should be able to reach my target of 100Khz even after adding the "front end" and some other features.

But right now these serial routines is making me go nuts....

[Ioannis]

Well, if you go from 20 to 40 MHz then your nice 60KHz is made with no pain 120KHz. That is more than 20% of your target, leaving you with a margin for the serial communication.

Why not try this first, to ease the pain?

Ioannis