McBSP Transmit

ALESSANDRO GUERRESCHI

Intellectual 580 points

Other Parts Discussed in Thread: DAC8568

Hi,

I am using the McBSP in SPI mode, with my TMSF28335 for communicate with the DAC8568.

I have configured the McBSP for use the DSP as a Master and I send a package of 32bit.

This is the configuration:

void InitMcBSPa(void)
{
 McbspaRegs.SPCR2.all=0x0000; // Reset FS generator, sample rate generator & transmitter
 McbspaRegs.SPCR1.all=0x0000; // Reset Receiver, Right justify word, Digital loopback dis.
 McbspaRegs.PCR.all=0x0F08; // (CLKXM=CLKRM=FSXM=FSRM= 1, FSXP = 1)
 McbspaRegs.SPCR1.bit.DLB = 1;
 McbspaRegs.SPCR1.bit.CLKSTP = 2;
 McbspaRegs.PCR.bit.CLKXP = 1; // IF 0 Transmit data is sampled on the rising edge of CLKX.
 McbspaRegs.PCR.bit.CLKRP = 1; // IF 1 Receive data is sampled on the rising edge of MCLKR.
 McbspaRegs.RCR2.bit.RDATDLY = 1; // FSX setup time 1 in master mode. 0 for slave mode (Receive)
 McbspaRegs.XCR2.bit.XDATDLY = 1; // FSX setup time 1 in master mode. 0 for slave mode (Transmit)

 McbspaRegs.RCR1.bit.RWDLEN1 = 0x5; // 32-bit word
 McbspaRegs.XCR1.bit.XWDLEN1 = 0x5; // 32-bit word

 McbspaRegs.SRGR2.all = 0x2000; // CLKSM=1, FPER = 1 CLKG periods
 McbspaRegs.SRGR1.bit.FWID = 0; // Frame Width = 1 CLKG period
 McbspaRegs.SRGR1.bit.CLKGDV = 99; // CLKG frequency = LSPCLK/(CLKGDV+1) = 30MHz / 100 = 300kHz

 McbspaRegs.SPCR2.bit.GRST = 1; // Enable the sample rate generator
 delay_loop(100); // Wait at least 2 SRG clock cycles
 McbspaRegs.SPCR2.bit.XRST = 1; // Release TX from Reset
 McbspaRegs.SPCR1.bit.RRST = 1; // Release RX from Reset
 McbspaRegs.SPCR2.bit.FRST = 1; // Frame Sync Generator reset
}

void InitMcBSPaGpio(void)
{
 EALLOW;
 // Configure McBSPa as SPI

 EALLOW;
 GpioCtrlRegs.GPAMUX2.bit.GPIO20 = 2; // GPIO20 = MDXA (SPISIMO)
 GpioCtrlRegs.GPAMUX2.bit.GPIO21 = 2; // GPIO21 = MDRA (SPISOMI)
 GpioCtrlRegs.GPAMUX2.bit.GPIO22 = 2; // GPIO22 = MCLKXA (SPISIMO)
 GpioCtrlRegs.GPAMUX2.bit.GPIO23 = 2; // GPIO23 = MFSXA (SPISTE)


 GpioCtrlRegs.GPAPUD.bit.GPIO20 = 0; // Enable pull-up

 GpioCtrlRegs.GPAPUD.bit.GPIO21 = 0; // Enable pull-up
 GpioCtrlRegs.GPAQSEL2.bit.GPIO21 = 3; // Asynch input GPIO21 (MDRA)

 GpioCtrlRegs.GPAPUD.bit.GPIO22 = 0; // Enable pull-up
 GpioCtrlRegs.GPAQSEL2.bit.GPIO22 = 3; // Asynch input GPIO22 (MCLKXA)

 GpioCtrlRegs.GPAPUD.bit.GPIO23 = 0; // Enable pull-up


 EDIS;
}

For send data:

void send_DAC_McBSPa(Uint32 send_data){


// send 1 packages with McBSPa (in SPI mode)
while( McbspaRegs.SPCR2.bit.XRDY == 0 ) {} // wait for any previous SPI transactions to clear
McbspaRegs.DXR1.all = send_data;

}

I have tried to send instead 32 bit package, two 16 bit packages. But the MFSXA goes high between the two packages and the DAC lost the communication.


This is a screenshot of what I see with the scope, is a fragment of the 32bit package, the last 16 bit are always low. (the CLK has 32 edges, so the DAC

can read correctly the package, but the value of the package result wrong being the last 16 bit at 0)

Could someone help me please? Thank you!

over 13 years ago

0 Kris Parrent over 13 years ago

TI__Genius 15260 points

Alessandro,

The last few lines of your post describing your actual problem got cut off. This tends to happen when copy and pasting code. Please just shorten those lines so I can read the full description. Thanks,

Kris

0 ALESSANDRO GUERRESCHI over 13 years ago in reply to Kris Parrent

Intellectual 580 points

Hi! Thanks! So:

The problem is that I have seen on the scope that at the output pin the package of 32 bit

that I send using the istruction:

while( McbspaRegs.SPCR2.bit.XRDY == 0 ) {} // wait for any previous SPI transactions to clear
McbspaRegs.DXR1.all = send_data;

has the first 16 bit correct, but the other 16 bits are all 0!

I can't understand why! The variable send_data is Uint32 and should be works!

Thank you for your help!

0 Kris Parrent over 13 years ago in reply to ALESSANDRO GUERRESCHI

TI__Genius 15260 points

Alessandro,

Ah I believe this is a simple fix. When you are using 32 bit mode, you need to use both the DXR1 and DXR2 registers. Each register is 16 bits, but they will send continuously. Note, the order in which you read and write both the DXR and DRR registers is important. I believe if you change your transmit to something similar to:

void mcbsp_xmit(int a, int b)
{
    McbspaRegs.DXR2.all = b;
    McbspaRegs.DXR1.all = a;
}

Then this should work.  Basically, DXR2 wasn't being written and had a value of '0'

 so you were sending all '0's for those 16 bits.

Kris

0 ALESSANDRO GUERRESCHI over 13 years ago in reply to Kris Parrent

Intellectual 580 points

Ah, thanks!

Now here it is evening, tomorrow I will come back to the office and I will proof immideately this change!

Ah, so with this configuration:

 McbspaRegs.RCR1.bit.RWDLEN1 = 0x5; // 32-bit word
 McbspaRegs.XCR1.bit.XWDLEN1 = 0x5; // 32-bit word

It send the data that has been written in DXR1 and in DXR2, and if I have to send only 16 bit

 (changing these register)

it send the data that has been written only in DXR1.

Thanks, I will update you tomorrow!

0 ALESSANDRO GUERRESCHI over 13 years ago in reply to ALESSANDRO GUERRESCHI

Intellectual 580 points

Yes, it works! Thank you Kris!

For people who have to use the DAC8568 with McBSP as SPI, the right configuration is:

McbspaRegs.SPCR1.bit.CLKSTP = 2;
 McbspaRegs.PCR.bit.CLKXP = 0; 
 McbspaRegs.PCR.bit.CLKRP = 0;

0 Kris Parrent over 13 years ago in reply to ALESSANDRO GUERRESCHI

TI__Genius 15260 points

Great, glad I could help. Thank you for following up with the solution.

Kris

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