SPI problem with BMI160

[SaberKazemi1992]

I am trying to have SPI connectio as interface protocol between BMI160 shuttle board/MSP432P401R. What I need is the accel/gyroscope data continuously.  The main functions I am using is from BMI160 drivers found on github:

https://github.com/BoschSensortec/BMI160_driver 

I have defined the user_spi_read/user_spi_write as below:

int8_t user_spi_write(uint8_t dev_id, uint8_t reg_addr, uint8_t *reg_data, uint16_t len)
{
int8_t rslt = 0; /* Return 0 for Success, non-zero for failure */
SPI_BMI160_BEGIN;
/* send register address byte */
SPI_BMI160_TX(reg_addr);
/* Storing chip status */
// SPI_BMI160_RX(rslt);
for (i = 0; i < len; i++)
{
SPI_BMI160_TX(*reg_data);
reg_data++;
}
return (rslt);

}

And

int8_t user_spi_read(uint8_t dev_id, uint8_t reg_addr, uint8_t *reg_data, uint16_t len)
{
int8_t rslt = 0; /* Return 0 for Success, non-zero for failure */
int i;
/* Pull CS_N low*/
SPI_BMI160_BEGIN;
/* send register address byte */
SPI_BMI160_TX(reg_addr);
/* Storing chip status */
//SPI_BMI160_RX(rslt);/////////////////?????
/* Communicate len number of bytes: if RX - the procedure sends 0x00 to push bytes from slave*/
for (i = 0; i < len; i++)
{
SPI_BMI160_TX(0); /* Possible to combining read and write as one access type */
// SPI_WAIT_DONE();
SPI_BMI160_RX(*reg_data); /* Store pData from last pData RX */
reg_data++;
}
//}
/* Pull CS_N low*/
SPI_BMI160_END;
/* return the status byte value */
return(rslt);
}

The functions for SPI (in MSP432p401R) abbreviated as below:

#define SPI_BMI160_BEGIN              P6OUT &= ~BIT2;
#define SPI_BMI160_TX(x)                do{while(!(UCTXIFG & UCB1IFG));UCB1TXBUF= (x);}while(1==-1)
#define SPI_BMI160_RX(x)                do{while(!(UCRXIFG & UCB1IFG));(x)=UCB1RXBUF;}while(1==-1)
#define SPI_BMI160_END                   P6OUT |= BIT2;

Is this correct form for SPI wirte/read functions? Seems SPI is not working.

Thanks

Saber

[shellywang]

It is recommended to observe the waveform using a logic analyzer or oscilloscope.

Here are some suggestions in terms of the code:

1. After power-on reset, the BMI160 is in I2C state by default. Therefore, a dummy read of register 0x00 is required to switch to SPI bus.
2. For write operations, reg_address should be ANDed with 0x7f and then sent out. For example, to write the address 0x40, 0x40 is ANDed with 0x7f, i.e.  0x40 & 0x7f, and the result 0x40 is sent out.
3. For read operations, reg_address should be ORed with 0x80 and then sent out. For example, to read the address 0x40, 0x40 is ORed with 0x80, i.e. 0x40 | 0x80, and the result 0xC0 is sent out.

[SaberKazemi1992]

Thanks for your previous reply. 

On 2 and 3, you mentioned that for read/write operations, the registers need to be ORed/ANDed with 0x7F/0x40 respectively. Does it apply to I2C as well?

Thanks

Saber

[o_o]

No. Only for SPI.

Background: In i2c the R/W bit is part of the address byte. In SPI, there is no address byte and the R/W bit is part of the command byte.

o_o

[SaberKazemi1992]

Hello

Thanks for your previous answer. Maybe a trivial question 🙂:

In #1, you mentioned to switch to SPI, a dummy read of 0x00 should be done. Can you please explain how I can do it?

The SPI write and read instances are like below:

int8_t user_spi_write(int8_t dev_id, int8_t reg_addr, int8_t *reg_data, int8_tlength)
{
int8_t rslt = BMI160_OK; /* Return 0 for Success, non-zero for failure */
SPI_BMI160_BEGIN;
SPI_BMI160_TX(reg_addr & 0x7F);
__delay_cycles(200);

for (i = 0; i < length; i++)
{
SPI_BMI160_TX(*reg_data);
reg_data++;
}
SPI_BMI160_END;

return rslt;
}

int8_t user_spi_read(int8_t dev_id, int8_t reg_addr, int8_t *reg_data, int8_tlength)

{

int8_t rslt = BMI160_OK; /* Return 0 for Success, non-zero for failure */

SPI_BMI160_BEGIN;

SPI_BMI160_TX(reg_addr | 0x80);
__delay_cycles(200);

for (i = 0; i < length; i++)
{
SPI_BMI160_TX(0); 
SPI_BMI160_RX(*reg_data); /* Store pData from last pData RX */
reg_data++;
}
SPI_BMI160_END;

return rslt;

}

Thanks

Saber