LAUNCHXL-F28379D: How can we communicate with more than three SPI devices in TMS320F28379D by using the standard SPI libraries

Hi,

Any update?

Is it possible to use other GPIOs to generate clock on other GPIO pins which are not configured as SPIA, B or C, so that we can use them for SPI communication?

Hi Gautham,

Apologies for the delay. The F28379D has a total of 3 SPI instances. There are also 2 MCBSP instances, which is a separate serial communication peripheral that can be used in SPI mode (please refer to the TRM for more information, this may not support all use cases). The list of available SPI pins is large due to the MUXing of pins and is not directly indicative of how many SPIs can be configured.

Regarding your 2nd question, it is possible to have the chip select ie PTE controlled by a GPIO instead of hardware. By doing this, you can connect 1 controller/master SPI to 'n' peripheral SPIs (without needing 'n' masters). Is this similar to what you're trying to implement? Or do you strictly need more (& complete) SPI instances? 

Thanks,

Arnav

Hi Arnav,

Thank you for clarification w.r.t MCBSP.

We have made a custom board with TMS320F28379D, wherein, we are communicating with a device which works on SPI, however, we are only required to use SCLK and MISO. we have 2 devices which are connected as below:

Device 1:

GPIO 14 - SCLK; GPIO 15 - MISO

Device 2:
GPIO 38 - SCLK; GPIO 39 - MISO

Since, these Pins are not related to SPIA, B or C, we tried toggling the pins to generate clock and get the data from the device, however, the minimum pulse which we could get by toggling GPIO 14 and GPIO 38 is 1.3 microsecond. 

How can we reduce this further? TRM says, GPIOs can be toggled with 25MHz frequency.

Hi,

Any update on this?

Hi,

Arnav Menon R Benjamin Collier can you help us out on this?

Hi Gautham,

The toggle frequency you're seeing is likely due to the optimization level used. Can you check the same with a higher compiler optimization level applied?

Regarding your setup, since you need MISO, you plan to use both F28379Ds as slaves, correct? In that case, why are you required to also generate clock pulse from these devices? If you could clarify how you intend to emulate the SPI, would be helpful. 

Thanks,

Arnav

Hi Arnav Menon R,

The optimization level was off, we switched it on and tried different settings and we were able to achieve GPIO toggle frequency upto 300ns., which will suffice. However, we have some follow up questions based on some observation after applying optimization. Some background on our project:

We are using TMS320F28379D to control a BLDC motor, we have an encoder and the output of encoder is in SPI format, however, only 2 SPI lines are used for the communication, CLK and MISO. We have verified the output of the encoder both using standard SPI libraries and also using GPIO pins and it is working correctly.

Observation:

On selecting different options in optimization level, we observed that the GPIO toggles at approximately 4 times the frequency when optimization was off, however, encoder output changed, instead of 0 to 360 degrees (which we get when optimization is OFF), we get 0 to 180 range only and in some other optimization options, we were getting 0 to 90 degrees only, finally we managed to find out that selecting Register optimization level and that too range set to 0 (between 1 to 5), we were getting correct output.

How does changing different optimization have an effect on how the code is being read from encoder?

Hi Arnav Menon R,

Any update?

Arnav Menon R

Hi,

Benjamin Colomer can you help us on this?

Hi,

Benjamin Collier  Arnav Menon R

 any update on this?