Tm4c123 as SPI slave

Hi,

I have an SPI master sending me commands and want to initialise the LM4F232 processor as a slave. I am using the LM4F232 Eval board for this purpose.

Following is the code for SPI initialisation as a slave.

void InitGPIOF(void)
{
GPIO_PORTF_LOCK_R = 0x4C4F434B; //Enable writing to GPIOCR registers
GPIO_PORTF_CR_R = 0x000000FF;

GPIOPinConfigure(GPIO_PF2_SSI1CLK);
GPIOPinConfigure(GPIO_PF3_SSI1FSS);
GPIOPinConfigure(GPIO_PF0_SSI1RX);
GPIOPinConfigure(GPIO_PF1_SSI1TX);

GPIOPinTypeSSI(GPIO_PORTF_BASE, GPIO_PIN_0 | GPIO_PIN_1 | GPIO_PIN_2 | GPIO_PIN_3);
}
void InitSPI(void)
{
U32 ulRcvdData[2];

SSIDisable(SSI1_BASE);
SSIConfigSetExpClk(SSI1_BASE, SysCtlClockGet(), SSI_FRF_MOTO_MODE_0, SSI_MODE_SLAVE, 125000, 8);

while(SSIDataGetNonBlocking(SSI1_BASE, ulRcvdData))
{

}

SSIIntEnable(SSI1_BASE, SSI_RXTO);
SSIIntRegister(SSI1_BASE, ISR_SpiInterrupt);
IntEnable(INT_SSI1);
SSIEnable(SSI1_BASE);
}

I want to receive single bytes from the master so I am using an SPI receive timeout interrupt.

Following is the interrupt service routine.

void ISR_SpiInterrupt(void)
{
U32 ulSPI_IntStatus = RESET;
ulSPI_IntStatus = SSIIntStatus(SSI1_BASE, TRUE);
SSIIntClear(SSI1_BASE, ulSPI_IntStatus);
g_stApolloParms.m_ulSPI_RcvdInt = YES;
}
And the while 1 loop:

if(g_stApolloParms.m_ulSPI_RcvdInt == YES)
{
g_stApolloParms.m_ulSPI_RcvdInt = NO;
GPIOPinWrite(GPIO_PORTD_BASE, GPIO_PIN_3, ~(GPIOPinRead(GPIO_PORTD_BASE, GPIO_PIN_3)));
}

I am facing multiple problems with this.

1. The SPI interrupt does trigger, but continously - I can see the PORTD, Pin 3 toggling all the time. The SPI master sends me one byte every 10ms.
2. Whenever I try to read any data after the interrupt is received, the interrupt does not trigger again - This is the case even if I use any of SSIDataGet(), SSIDataGetUnblocking, or even directly reading the SSI1_DR_R register.
3. On the SSI_TX line is always low.

Just to make sure that my connections are proper, I have connected the system in the following manner.
1. SSICLK - SCLK (Masterclock)
2. SSIRX - MOSI (On the master side)
3. SSITX - MISO (On The master side)
4. SSIFSS is pulled low.

I do not know what I am missing or what is going wrong. Kindly help.

Just as an update, I have tried using 2 modules of SSI on the same controller with the same issues. Also, the SPI works correctly in loopback fashion..

Thanks and Regards,
Makarand