How to select CHIP SELECT pin of SPI driver of TI-RTOS

Soumyajit,

The application must manage the chip select itself. It is not managed in the SPI driver. We are looking at adding it in a future release. If you have multiple Tasks calling SPI_transfer (with the same SPI_Handle), you need to add protection around the calls. For example (in pseudo-code):

Semaphore_pend(csSemHandle)
Assert desired CS
SPI_transfer()
Deassert CS
Semaphore_post(csSemHandle)

Soumyajit Das said:

In the SSI3 module example of Tiva EK-TM4C1294XL, the CS pin is assigned to port pin PQ1 but I want to change it to pin PN4. How to do that?

I'll get back to you on this.

Todd

Soumyajit,

Soumyajit Das said:

In the SSI3 module example of Tiva EK-TM4C1294XL, the CS pin is assigned to port pin PQ1 but I want to change it to pin PN4. How to do that?

GPIOPinConfigure(GPIO_PQ1_SSI3FSS) is called in EK_TM4C1294XL_initSPI() assigns that pin into the peripheral's hardware mode. In other words, the SSI controller (in hardware) toggles this pin for you as specified in the TivaC's datasheet (the toggle format actually depends on the frame format used).

However, as PN4 is not multiplexed with the SSI3 controller's Fss pin, the hardware chip select is not an option. Instead however, PN4 needs to be configured as a GPIO output pin and then the application must toggle it manually before and after a SPI_transfer() call. This limitation is something that we are currently investigation to improve.