CCS/EK-TM4C1294XL: How to communicate with SPI Multi slaves using the CCS SSI driver library?

Hani Ahmed

Intellectual 555 points

Part Number: EK-TM4C1294XL
Other Parts Discussed in Thread: TM4C1294NCPDT

Tool/software: Code Composer Studio

I did configuration for the SPI2 for the TM4C1294NCPDT and tested it with one slave device with successful result.

here is copy of my configuration using the "driverlib/ssi.h" library:

// The SSI2 peripheral must be enabled for use.
SysCtlPeripheralEnable(SYSCTL_PERIPH_SSI2);

// Configure the pin muxing for SSI2 functions on port D
GPIOPinConfigure(GPIO_PD3_SSI2CLK);
GPIOPinConfigure(GPIO_PD2_SSI2FSS);
GPIOPinConfigure(GPIO_PD1_SSI2XDAT0); //GPIO_PD1_SSI2TX
GPIOPinConfigure(GPIO_PD0_SSI2XDAT1); //GPIO_PD0_SSI2RX

// Configure the GPIO settings for the SSI pins. This function also gives
// control of these pins to the SSI hardware.
// PD1 - SSI2Tx
// PD0 - SSI2Rx
// PD2 - SSI2Fss
// PD3 - SSI2CLK
GPIOPinTypeSSI(GPIO_PORTD_BASE, GPIO_PIN_3 | GPIO_PIN_2 | GPIO_PIN_1 |
GPIO_PIN_0);

SSIConfigSetExpClk(SSI2_BASE, SysCtlClockGet(), SSI_FRF_MOTO_MODE_0, SSI_MODE_MASTER, 1000000, 8);

// Enable the SSI2 module.
SSIEnable(SSI2_BASE);

my concern as I want to use the same above configuration with multi slaves.

But when i use SSIDataPut(SSI2_BASE, ui8DOTx[ui8Index]);

I discovered that there is no way to force the SPI driver library to change the slave select (Fss) to use another GPIO pin than the first configured.

So is there any solution for this other than using an external hardware?

over 5 years ago

0 Ralph Jacobi over 5 years ago

TI__Guru*** 135355 points

Hello Hani,

There is and it's actually quite simple. You should instead manually control the SS line with GPIO driverlib commands instead. This is actually not an uncommon practice as some applications benefit from manually GPIO SS control even with just a single device.

So your configuration would include configuring each of your SS GPIO as a simple GPIO output and setting them high initially.

Then on SPI writes, just pull the appropriate GPIO low before any SPI commands.

0 Hani Ahmed over 5 years ago in reply to Ralph Jacobi

Intellectual 555 points

Hello Ralph

I found example "soft_spi_master.c", so i think modification of it is same as the manual configuration, isn't it?

Hani

0 Ralph Jacobi over 5 years ago in reply to Hani Ahmed

TI__Guru*** 135355 points

Hello Hani,

No you would still use the SSI peripheal and not a software SSI if you did as I described. You just would control only the SS line manually. SPI CLK, MISO, and MOSI all would still be handled by the TM4C SSI peripheral.

0 Hani Ahmed over 5 years ago in reply to Ralph Jacobi

Intellectual 555 points

Dear Ralph

Understood that I should ignore the Fss pin and start use the SS as GPIO, right?

This means I will lose HW resource (Fss).

Thanks

Hani

0 Ralph Jacobi over 5 years ago in reply to Hani Ahmed

TI__Guru*** 135355 points

Hello Hani,

No you just don't configure that pin for the SSI peripheral then you can use it for the GPIO peripheral, so no need to lose HW resources or even change the pin itself. Its just changing which peripheral drives the pin (SSI vs GPIO).

0 Hani Ahmed over 5 years ago in reply to Ralph Jacobi

Intellectual 555 points

Hello Ralph

I tried to manually change the SSI2FSS pin but it seems its not respond to my GPIO configuration.

Hani

0 Ralph Jacobi over 5 years ago in reply to Hani Ahmed

TI__Guru*** 135355 points

Hello Hani,

Can you post the code you used to implement this change so I can review to see what may be missing?

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CCS/EK-TM4C1294XL: How to communicate with SPI Multi slaves using the CCS SSI driver library?