NCO square-wave output using Smartpin

Rayman

I wanted a 12.375 MHz square wave to drive the clock on an FTDI EVE3 chip.
Was pretty easy to do using the NCO smartpin mode.

Basically like this in FlexProp C:
in FlexProp C using inline assembly to create NCO on pin #8 (12.375 MHz with 297 MHz P2 clock):
__asm {
wrpin ## 0b00000000000000000000000011001100, #8 //smartpin NCO
WXPIN #12, #8 //base period
WYPIN ##$8000_0000, #8 //add amount per clock
drvh #8
}

I've made some notes on the math and the Spin2 version here.

JonnyMac

For those using Spin2 in PNut and Propeller Tool, you can do it like this:

  org
                wrpin   ##(P_OE | P_NCO_FREQ), #NCO_PIN
                wxpin   #12, #NCO_PIN
                wypin   ##$8000_0000, #NCO_PIN
                drvh    #NCO_PIN
  end

evanh

I'm the last person to advise on how to use Spin2 but the built-in Pinstart() function should do the job.
eg: PINSTART(NCO_PIN, (P_OE | P_NCO_FREQ), 12, $8000_0000)

Peter Jakacki

For those using TAQOZ and much the same with Tachyon on the P1 you can use this (using pin 8):

8 PIN 12,375 KHZ

Try it yourself interactively via the serial console.

Ariba

evanh wrote: »

I'm the last person to advise on how to use Spin2 but the built-in Pinstart() function should do the job.
eg: PINSTART(NCO_PIN, (P_OE | P_NCO_FREQ), 12, $8000_0000)

Exactly, and pinstart() works also in flex-C if you write it with a underscore at begin:

  _pinstart(8, P_NCO_FREQ+P_OE, 12, 0x8000_0000);

Andy

Rayman

I did not know about pinstart!
Thanks!

JonnyMac

evanh wrote: »

I'm the last person to advise on how to use Spin2 but the built-in Pinstart() function should do the job.
eg: PINSTART(NCO_PIN, (P_OE | P_NCO_FREQ), 12, $8000_0000)

You're absolutely right. I have recently been porting P1 laser tag code to the P2, and have setup my IR modulation pins manually so that I can control when the oscillation starts. In this case, it is desired right away, so pinstart() is appropriate.

pub set_freq(port, hz) 

'' Sets output frequency for selected port(s), 1, 2, or 3 (both)
'' -- application should check for not busy before changing frequency
'' -- setting frequency to 0 disables port

  if (tx1p >= 0)                                                ' port 1 pin defined?
    if ((port == CMD_P1) || (port == CMD_P3))                   ' update port 1 frequency?
      pinclear(tx1p)                                            ' clear settings
      if (hz > 0)
        wrpin(tx1p, P_NCO_FREQ | P_OE)                          ' NCO with output
        wxpin(tx1p, 1)
        wypin(tx1p, hz frac clkfreq)                            ' set frequency

  if (tx2p >= 0)
    if ((port == CMD_P2) || (port == CMD_P3))
      pinclear(tx2p)
      if (hz > 0)
        wrpin(tx2p, P_NCO_FREQ | P_OE)
        wxpin(tx2p, 1)
        wypin(tx2p, hz frac clkfreq)

Rayman

I've added PINSTART and the predefined constant info to my webpage, thanks.