IWR6843: SPI CS signal behaviour

Swapnil

Part Number: IWR6843
Other Parts Discussed in Thread: LP87745-Q1

Hello Community,

I am working with the custom board where IWR6843 is connected with LP87745-Q1 PMIC via SPI.

When I am trying to write on the PMIC user register on address 0x0A with data 0x9B to unlock the register, I am getting unexpected behavior from CS signal and hence the write is not successful.

After writing 0x9B on address 0x0A I am expecting 0x10EF00 as response on SDO line whereas I am getting 0x101010, which just first byte getting repeated two times.

I am guessing its because after every 8-bit CS is going high for few micro seconds and thats why maybe PMIC is understanding it as end of transmission and sending again same first byte.

For SPI I am using data size 8 bit here.

Below is the signal pattern observed on oscilloscope

Expected behaviour from SPI driver when writing to PMIC.

The above diagram is from the complete datasheet of LP87754.

It is the same behavior while reading as well from the user register address.

When using 8-bit data size I could read only the first byte 0x10. Whereas when I use 16-bit data size I could read 0x10EF but not the third byte. The same two bytes get repeated again.

Not sure if it's the problem with SPI driver behavior here.

Thanks and Regards,

Neil

over 1 year ago

0 Alec May over 1 year ago

TI__Genius 17265 points

Hi Neil,

Can you share the following info so that we can debug this a bit further?

mmWave SDK version
SPI driver configuration

Best Regards,
Alec

0 Swapnil over 1 year ago in reply to Alec May

Intellectual 350 points

Hello Alec,

Thank you for your reply.

1. mmWaveSDK Version: 3.5.0.4

2. SPI Driver configuration:

params.mode = SPI_MASTER;

params.u.masterParams.bitRate = 1000000U;
params.u.masterParams.numSlaves = 1;
params.u.masterParams.slaveProf[0].chipSelect = 0;
params.u.masterParams.slaveProf[0].ramBufLen = 64U;
params.u.masterParams.slaveProf[0].dmaCfg.txDmaChanNum =1U;
params.u.masterParams.slaveProf[0].dmaCfg.rxDmaChanNum =0U;

params.u.masterParams.c2tDelay = 0x5;
params.u.masterParams.t2cDelay = 0x5;
params.u.masterParams.wDelay = 0;

/* Enable DMA and set DMA channels */
params.dmaEnable = 1;
params.dmaHandle = gDmaHandle;
params.dataSize = 8;

params.frameFormat = SPI_POL0_PHA1;
params.pinMode = SPI_PINMODE_4PIN_CS;

I have used this above configuration of SPI for to for interfacing IWR6843 with LP87754.

Thanks and Regards,

Neil

0 Alec May over 1 year ago in reply to Swapnil

TI__Genius 17265 points

Neil,

Your configuration looks fine to me. After digging around the driver a bit, I see that for our devices we set the SPIDEF register to all 1's, which means that the CS value will be set to 1 whenever the SPI module is idle. Perhaps there is a few microseconds after the first byte where the SPI module believes it is idle, and sets the CS value to its default value?

In order to debug this, you would need to include the SPI driver into your project and rebuild it. If you want to try this, you would want to modify the following line of mibspi_dma.c