TMS320F28069M: Integrate SCI with Instaspin

Dave Reagan said:

if the interrupts keep interrupting it, and I can't use DMA?

No. DMA doesn't support the SCI. You may try to use the SCI FIFO if the frame data length is less than 16 bytes.

Hi Yanming,

The maximum number of symbols that the receive data frame could likely assume is about 47 bytes.

Is there some technique whereby I could collect data on the serial port while these interrupts are firing off every 66us?

There’s McBSP, but that requires 6 pins and looks kind of like SPI, with its own CLK to gate data in & out. That would require another board spin, and I think management is beginning to lose patience with me on that front. We’d also have to get the subcontractor who wrote the LCD firmware to alter their code (and perhaps their board layout), in order to accommodate the new scheme. Further complicating things, the guy that wrote the code for them has moved on to another company.

Barring the use of DMA (and therefore McBSP), I could lower the ISR repetition rate to 10kHz (30kHz PWM). That way if I wanted to, at least occasionally, pick up a message from the LCD, I’d have to be able to fit, say, 40 bytes into 100us. That’s 3.2 MegaBAUD. LSPCLK/16 is the maximum BAUD rate for the TMS320 – that’s 5.6MegaBAUD. So, I guess it could be done, as long as the micro in the LCD module is capable of that as well. One value that seems like it might be reasonable is 3.686MegaBAUD.

But I hate that it would become some statistical game of chance at this point. I should be able to receive and send messages predictably via the serial ports. Otherwise, what's the point of having this technique called InstaSpin? It seems the only thing you can use it for is a constant speed that the user can't reliably change. Unless, of course, you knew beforehand that serial comm wouldn't work; that you'd have to use McBSP and DMA. There should be a warning at the beginning of the User's Manual, in bold print, in bright Red, letting us know that there's only one way to communicate serially with the system, and that's via McBSP. Technically I guess JTAG could be used as well, but we can't ship an XDS110 and a laptop with every product.

Right now, though, I'm stuck with using the UART. Do you know of some technique to reliably use it?

Thanks,

Dave

Is it possible to use SPI for this communication? The SPI can support DMA.

Or you may refer to the example in C2000Ware to use nested interrupt method. You can enable SCI RX and TX interrupts to nest the interrupt for motor control, but try to short the RX and TX ISR execution time.

Hi Yanming,

At this stage I can't use SPI. That would require another board spin for me, and for the subcontractor that developed the LCD Module.

I'll look into nested interrupts, but I thought the TMS320F28069M was not capable of that?

Thanks,

Dave