Smart Pin DAC

John Abshier · 2019-04-19 17:39

CON
            
    oscmode = $010c3f04               'standard stuff
    freq    = 160_000_000

pub main     | pMode, outVal, period, thePin
    clkset(oscmode, freq)
    thePin := 41
    pMode := %0000_0000_000_10100_00000000_01_00010_0     'Random dither
'    pMode := %0000_0000_000_10100_00000000_01_00011_0     'PWM dither
    period := 32768                      
    outVal := 16384                 
    asm
       dirl     thePin
       wrpin    pMode,     thePin
       wxpin    period,    thePin
       wypin    outVal,    thePin
       dirh     thePin
    endasm 
    repeat

I have tried various values of period and outVal but my Propscope fails to trigger. If I turn the trigger off the Propscope measures -9 to 19 mVolts. I tried a simple program to toggle the pin at 1000 hz and the Propscope picked it up fine. I don't know what I am missing.

John Abshier

Peter Jakacki · 2019-04-19 18:45

Try shifting your data value to wypin up by 16 bits left into the msbs. (can't sleep, I will look at it again to see what's wrong).
You need immediate values since period and outVal etc are global variables only. (I think)

This is a simple DAC function in TAQOZ.

pub DAC ( bits -- )		%101_000_0000000_01_00011 WRPIN |< WXPIN ;
pub V ( volts*1000 --- )	16 << 3300 U/ WYPIN ;

So the first line is equivalent to WYPIN ##%101_000_0000000_01_00011,#thePin and also WXPIN ##1<<12,#thePin.

Setup:

32 PIN 12 DAC

To set pin to 1.850V

1.850 V

ozpropdev · 2019-04-20 00:42

Your code should be using '#' for immediate values. Peter's on to it

dirl     #thePin
       wrpin    ##pMode,     #thePin
       wxpin    ##period,    #thePin
       wypin    ##outVal,    #thePin
       dirh    #thePin

ersmith · 2019-04-20 02:46

ozpropdev wrote: »
Your code should be using '#' for immediate values. Peter's on to it
dirl     #thePin
       wrpin    ##pMode,     #thePin
       wxpin    ##period,    #thePin
       wypin    ##outVal,    #thePin
       dirh    #thePin

No, that's not it: pMode, period, outVal, and thePin are all variables, i.e. registers, so putting "#" in front of them will definitely not do what you want -- it'll cause the address of the variables to be used rather than their values.

I don't know off-hand what's wrong, and don't have my P2 handy, but the values for period and outVal look wrong to me. I think generally there should be something in the upper 16 bits, but the sample code above has 0 there.

ozpropdev · 2019-04-20 02:54

Ah, I'm looking at the code from a Pnut pasm perspective(That's all I use).

John Abshier · 2019-04-20 03:14

From Propeller 2 Documentation v32.pdf

%00010 and DAC_MODE = DAC 16-bit with pseudo-random dither
This mode overrides P[7:0] to feed the pin’s 8-bit DAC with pseudo-randomly-dithered data on every clock. P[12:10] must be
set to %101 to configure the low-level pin for DAC output.
X[15:0] establishes the sample period in clock cycles.
Y[15:0] establishes the DAC output value which gets captured at each sample period and used for its duration.

I will be out of town the next 2 1/2 days and unable to test but will follow the forum.

John Abshier

John Abshier · 2019-04-20 03:36

Here is a program where I tried to use the P value to set the DAC level. But still no joy.

CON
            
    oscmode = $010c3f04               'standard stuff
    freq    = 160_000_000

pub main     | pMode, outVal, period, thePin
    clkset(oscmode, freq)
    thePin := 41
    '         AAAA BBBB FFF PPPPP PPPPPPPP TT MMMMM
    pMode := %0000_0000_000_10100_01000000_00_00000_0     
    asm
       dirl     thePin
       wrpin    pMode,     thePin
       dirh     thePin
    endasm 
    
    repeat 
    
{       dirb[thePin] := 1           ' code to test Propscope comment out the above assymbler code 
       !outb[thePin] 
       waitcnt(cnt + clkfreq / 1_000_000)}

John Abshier

Peter Jakacki · 2019-04-20 03:53

This is the mode I use: %101_000_0000000_01_00011_0

Read the section in the doco about these modes when using the DAC.

evanh · 2019-04-20 04:55

John Abshier wrote: »
Here is a program where I tried to use the P value to set the DAC level. But still no joy.
'         AAAA BBBB FFF PPPPP PPPPPPPP TT MMMMM
    pMode := %0000_0000_000_10100_01000000_00_00000_0     
    asm
       dirl     thePin
       wrpin    pMode,     thePin
       dirh     thePin
    endasm 

That works for me. Here's my pure pasm version and a screenshot from the scope.

evanh · 2019-04-20 05:00

Here's a cleaner version that doesn't repeatedly disable the pin

_main
		dirl	pin
		wrpin	pincfg, pin
		dirh	pin
_loop
		waitx	sec
		getrnd	count
		setbyte	pincfg, count, #1

		wrpin	pincfg, pin
		jmp	#_loop

John Abshier · 2019-04-20 18:51

Evanh, this is what I think your program does, but I am not an assembly guy. It looks like you are looping 4 times per second. But the scope trace looks like 2 loops per second. Output is to pin 0. Each time through the loop you replace the last byte of pincfg with a random byte to set the DAC level. Did I read your code correctly?

John Abshier

evanh · 2019-04-21 01:12

Oops, good catch, that's buggy code. In my rush to shorten the size of my default working environment I deleted one line I shouldn't have. It shouldn't be working like that.

The ORGH should be ORGH $400.

Mark_T · 2019-04-21 18:22

You don't use DIRH for dithered dac mode. Smartpin modes take over the function of OUTx and DIRx
registers and may give them alternate uses. Both dithered DAC modes are smartpin modes.

Raw DAC mode (not dithered) is not a smartpin mode so will require DIRH as I understand it. The MMMMM
bits have to be non-zero for smartpin operation.

I think that's right. Certainly my code using dither modes doesn't touch DIRx or OUTx

Mark_T · 2019-04-21 18:23

Mark_T wrote: »

You don't use DIRH for dithered dac mode. Smartpin modes take over the function of OUTx and DIRx
registers and may give them alternate uses. Both dithered DAC modes are smartpin modes.

Raw DAC mode (not dithered) is not a smartpin mode so will require DIRH as I understand it. The MMMMM
bits have to be non-zero for smartpin operation.

I think that's right. Certainly my code using dither modes doesn't touch DIRx or OUTx, just uses WRPIN and WYPIN

John Abshier · 2019-04-21 19:46

Mark T, could you please post your code?

John Abshier

evanh · 2019-04-21 21:16

In my examples the first DIRH is needed to first enable pin drive. Repeated DIRL/DIRH combos will repeatedly disable/enable the pin drive.

Mark might be correct when using %TT = 01. This basically forces DIRH for that pin. When in a DAC mode the OUT becomes an ADC enable.

Err, reading the docs, %TT = 01 in DAC mode means config for SETDACS operation:

	for smart pin mode off (%MMMMM = %00000):

		DIR enables output

		for non-DAC_MODE:
			0x = OUT drives output
			1x = OTHER drives output

		for DAC_MODE:
			00 = OUT enables ADC, P[7:0] sets DAC level
			01 = OUT enables ADC, P[3:0] selects cog DAC channel
			10 = OUT drives BIT_DAC, drives two levels, P[7:0] sets DAC high level, #0 is low level
			11 = OTHER drives BIT_DAC, drives two levels, P[7:0] sets DAC high level, #0 is low level

And some additional info from the pad_io_modes

	%101_VV_DDDDDDDD = DAC_MODE (%TT = 00 and %MMMMM = 00000), 8-bit flash
		OUT enables PinA ADC (ADC config %011), sysclocked bitstream on IN
		DIR enables PinA DAC output
		%VV = PinA drive config
			00: 990 ohm, 3.3 volt range
			01: 600 ohm, 2.0 volt range
			10: 123.75 ohm, 3.3 volt range
			11: 75 ohm, 2.0 volt range
		%DDDDDDDD = DAC level

		for %TT = %01 and %MMMMM = %00000, %101_VV_xxxxSSSS = COG_DAC mode
			%SSSS = Cog/streamer select: sets DAC level (registered?)

Mark_T · 2019-04-22 15:55

John Abshier wrote: »

Mark T, could you please post your code?

John Abshier

con
  pin = 56
  freq = 160_000_000
  mode = $010c3f04
  delay = freq / 100000

  prng = %0000_0000_000_10100_00000000_01_00001_0
  dither = %0000_0000_000_10100_00000000_01_00010_0    ' remember to wypin
  dither_pwm = %0000_0000_000_10100_00000000_01_00011_0    ' remember to wypin
  dac  = %0000_0000_000_10100_00000000_00_00000_0

dat
    org

    ' set up clock
    hubset #0
    hubset ##mode  ' initialize oscillator
    waitx ##20_000_000/100 ' wait for it to settle down
    hubset ##mode + %11   ' enable it 

    mov    val, #0
    wrpin   ##dither_pwm, #48
    wxpin   #0, #48

    ' now loop forever blinking the pin
    rep @done, #0
    drvnot #pin

    waitx ##delay
    add   val, #1
    and   val, #$FF
    mov   t, val
    xor   t, #$E7
    shl   t, #8
    wypin t, #48
done

val	long	0
t       long    0

An old test file, the loop is generating a somewhat random step function using add, xor I think, in pwm dither mode
(I think the wxpin is unnecessary)

John Abshier · 2019-04-22 20:14

I am getting really frustrated. Mart T's code produces a repeating stairstep output. I just want a fixed output value, say 1/2 voltage. I set val to 128 and commented out the code that changes the value written with wypin. Result is 29 to 49 milliVolts. I was expecting 3.3/2 volts. Here is the modified code. Changed lines have ***********

mov    val, #128  '#0                        ******************
    wrpin   ##dither_pwm, #48
    wxpin   #0, #48

    ' now loop forever blinking the pin
    rep @done, #0
    drvnot #pin

    waitx ##delay
'    add   val, #1                             *********************
'    and   val, #$FF                           *********************
    mov   t, val
'    xor   t, #$E7                             *********************
'    shl   t, #8                               *********************
    wypin t, #48
done

John Abshier

Tubular · 2019-04-22 21:12

Hi John,

For what you want, just set WRPIN to set the static DAC level. wypin isn't required and may be causing issues

nxtdac		mov	i, j
		shl	i,#8
		or	i, pinmode	'overlay DAC pin command
		wrpin	i,p		'set pin to DAC output mode
		drvh	p		'output high 
		
		call	#pulsevm

		add	j,#1
		cmp	j,#256 wcz
	if_ne	jmp	#nxtdac

in the code above 'j' is the static level 0 to 255
pinmode starts as

pinmode		long	%0000_0000_000_10100_00000000_00_00000_0 + dacnum<<16	'DAC3 75R

Note that if you output 128 you'll get around 1.65 or 1.0 volts depending on which dac you're using

Full working code we used for stepping through multiple dacs and every pin attached. The pulsevm sends a pulse to the multimeter to take a reading

John Abshier · 2019-04-22 22:28

Tubular, you gave me the essential magic piece of information that I needed. Thanks very much. I was doing a dirh and what I needed was a drvh. My goal was to write a simple analog to the Arduino AnalogWrite function. I now have an 8 bit (0-255) version working and tested for modes 00: 990 ohm, 3.3 volt range and 01: 600 ohm, 2.0 volt range. Modes 10: 123.75 ohm, 3.3 volt range and 11: 75 ohm, 2.0 volt range didn't work, but I don't care. I think I have the 16 bit random dither mode working, but need to test. Ultimate goal is a simple to use library that would make and Arduino user comfortable with switching to a Prop2.

John Abshier

Tubular · 2019-04-22 22:31

Looking back at your early code John, that should have worked ok. Other than the DIRL that shouldn't be required, I'm not sure why it wouldn't have worked. Suggest trying another pin and double checking the basics . The other weird thing is that Evanh's scope shot shows a moving output

Were you calling that pasm repeatedly on a tight loop? Or just once (just once should be fine)

Tubular · 2019-04-22 22:33

Ah yeah nasty, I didn't pick that up when looking back at your code, either.

Sounds like a worthy project, hope the remainder goes smoothly

evanh · 2019-04-23 00:32

My scope screenshot was for my extended example code that explicitly added the changing levels as a demo. Just to show the program was working and able to set the level.

I thought the looping/stepping nature was obvious and wouldn't cause confusion. John even correctly described it and identified a bug I had.

evanh · 2019-04-23 00:47

Here's a commented version

_main
		dirl	pin
		wrpin	pincfg, pin		initial DAC level set
		dirh	pin
loop
		waitx	sec			'puase for half second
		getrnd	count			'get a random number as next DAC level
		setbyte	pincfg, count, #1	'insert 8 bits of DAC level into pincfg data

		wrpin	pincfg, pin		'update DAC level
		jmp	#loop			'repeat from pause

evanh · 2019-04-23 01:08

John,
The way to make the OUT bit control the DAC level is to use what's called BIT_DAC mode. I'm guessing you may have accidentally done this already. There is mention of this in the main doc and here's the pad_io_modes write up continuing from earlier posting. Full write up - https://forums.parallax.com/discussion/comment/1452036/#Comment_1452036

		for %MMMMM >= %00100 or (%TT = %1x and %MMMMM = %00000) = BIT_DAC mode
			OUT sets DAC level (clocked?, ADC disabled?, IN = ?)
				0: 0 = GIO level
				1: %DDDDDDDD

An example would be:

pin		long	0
pincfg		long	%0000_0000_000_10100_00000000_10_00000_0  + 128 <<8	'128 is the preset


_main
		drvl	pin			'start with a low OUT
		wrpin	pincfg, pin		'config the preset DAC level
		dirh	pin
loop
		waitx	sec			'pause for half second
		outnot	pin			'toggle between 0 volt and preset DAC level
		jmp	#loop			'repeat from pause

Smart Pin DAC

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