K66 Doc error for DAC Top/Bottom flag bits

daleroberts — Wed, 01 Mar 2017 14:45:28 GMT

Hello, I think I have found a documentation error in the K66 Reference Manual. I am using a MK66FX1M0VMD18 on an Arduino Teensy 3.6. It looks like Top and Bottom pointer flags in the 12-bit DAC DACx_SR register (0x02-DACBFRPTF and 0x01-DACBFRPBF) and in DACx_C0 (0x02-DACBTIEN and 0x01-DACBBIEN) are documented backwards. I noticed this when trying to connect DMA to the DAC.

I verified this with a small Arduino program to step the DAC buffer pointer with a software trigger, and show the SR flags at each step (then clear the SR flags after each step). It shows the 0x01 bit going high at the TOP of the buffer (this is documented as the Bottom bit), and the 0x02 bit going high at the BOTTOM of the buffer (this is documented as the Top bit). The 0x04 water mark flag goes high correctly 4 words from the upper limit (which I have set to 8 here).

Program Output:

Initial: DAC0_SR:2 DAC0_C0:A0 DAC0_C1:19 DAC0_C2:08

0   DACBufPtr: 0   SR: 2
1   DACBufPtr: 1   SR: 0
2   DACBufPtr: 2   SR: 0
3   DACBufPtr: 3   SR: 0
4   DACBufPtr: 4   SR: 4     (Water Mark flag, correct)
5   DACBufPtr: 5   SR: 0
6   DACBufPtr: 6   SR: 0
7   DACBufPtr: 7   SR: 0
8   DACBufPtr: 8   SR: 1    (the "BOTTOM" bit triggers at the top of the buffer)
9   DACBufPtr: 0   SR: 2    (the "TOP bit triggers at the bottom of the buffer)
10   DACBufPtr: 1   SR: 0
11   DACBufPtr: 2   SR: 0
12   DACBufPtr: 3   SR: 0
13   DACBufPtr: 4   SR: 4
14   DACBufPtr: 5   SR: 0
15   DACBufPtr: 6   SR: 0
16   DACBufPtr: 7   SR: 0
17   DACBufPtr: 8   SR: 1
18   DACBufPtr: 0   SR: 2
19   DACBufPtr: 1   SR: 0

Complete working Arduino code:

void dprintf(const char *Format, ...);

//
// Initialize DAC0, set pointer to 0, and increment the pointer 20 times.
// After each increment, print out the Status Register to see which
// interrupts have been fired, then reset the SR interrupt flags.
//
void TestDacIRQ()
{
SIM_SCGC2 |= SIM_SCGC2_DAC0;    // enable DAC clock

DAC0_C0 = DAC_C0_DACEN | DAC_C0_DACTRGSEL;
DAC0_C1 = DAC_C1_DACBFWM(3) | DAC_C1_DACBFEN;
DAC0_C2 = 0x08;                 // Read pointer=0, max=8.

// Show initial state.
dprintf("Initial: DAC0_SR:%d DAC0_C0:%02X DAC0_C1:%02X DAC0_C2:%02X \n\n",
        DAC0_SR, DAC0_C0, DAC0_C1, DAC0_C2);

for(int i=0; i < 20; ++i) {
    // Show current DAC buffer pointer, and the Status Register.
    dprintf("%2d   DACBufPtr:%2d   SR:%2d \n",
            i, DAC0_C2>>4, DAC0_SR);

    DAC0_SR = 0;                  // Clear Status Register bits.
    DAC0_C0 |= DAC_C0_DACSWTRG;   // Software Trigger to step Buffer Pointer.
}
}

void setup() {
Serial.begin(9600);
for(int i=0; !Serial && (i < 50); ++i)
    delay(20);
TestDacIRQ();
}

void loop() { }

char spbuf[300];
void dprintf(const char *Format, ...)
{
va_list ap;
va_start(ap, Format);
vsnprintf(spbuf, sizeof(spbuf), Format, ap);
va_end(ap);
Serial.print(spbuf);
}

Re: K66 Doc error for DAC Top/Bottom flag bits

miduo — Fri, 10 Mar 2017 08:58:45 GMT

Hi,

Yes, it seems you are right on this issue,I had checked and agree with you. Anyway, I should double check with the application team and will response you & report the document bug if this been confirmed. Thanks for your information and sorry for the inconvenience this may had caused to you.

Re: K66 Doc error for DAC Top/Bottom flag bits

daleroberts — Fri, 10 Mar 2017 15:49:26 GMT

Thanks for looking into it. I am glad to be able to contribute to the community! And I really enjoy working with this chip. It is a little powerhouse!

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K66 Doc error for DAC Top/Bottom flag bits

Re: K66 Doc error for DAC Top/Bottom flag bits

Re: K66 Doc error for DAC Top/Bottom flag bits