lm4f120xl - SPI problem

Bartosz Szmit

I have a problem with my LM4F120XL. I need to connect it with IMU sensor LSM9DS0 via SPI.

I think that problem is with Chip Select.

Only several first reads are correct. Then I get 255. Quantity of correct reads depends of clock or bitRate (it varies from ~3 to 8) :

SSIConfigSetExpClk(SSI0_BASE, SysCtlClockGet() , SSI_FRF_MOTO_MODE_1, SSI_MODE_MASTER, 1000000, 8); ).

I have checked all SSI_FRF_MOTO_MODES - problem still exists.

I think the problem is with Chip Select lines

GPIOPinWrite(GPIO_PORTD_BASE, GPIO_PIN_6, 0x00); //select device
When I am not toggling CS pin, but instead set it low permanently in initialization, I've got correct reads.

Thanks for help in advance!

void SPIInit() {
	SysCtlClockSet(SYSCTL_SYSDIV_1 | SYSCTL_USE_OSC | SYSCTL_OSC_MAIN |
	                   SYSCTL_XTAL_8MHZ);
	SysCtlPeripheralEnable(SYSCTL_PERIPH_SSI0);
	SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOA);
	GPIOPinConfigure(GPIO_PA2_SSI0CLK);
	GPIOPinConfigure(GPIO_PA3_SSI0FSS);
	GPIOPinConfigure(GPIO_PA4_SSI0RX);
	GPIOPinConfigure(GPIO_PA5_SSI0TX);
	GPIOPinTypeSSI(GPIO_PORTA_BASE, GPIO_PIN_5 | GPIO_PIN_4 | GPIO_PIN_3 |
	GPIO_PIN_2);

	SSIClockSourceSet(SSI0_BASE, SSI_CLOCK_SYSTEM);
	SSIConfigSetExpClk(SSI0_BASE, SysCtlClockGet()/1 , SSI_FRF_MOTO_MODE_1,
	SSI_MODE_MASTER, 1000000, 8);

	//cs pins
	SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOD);
	GPIOPinTypeGPIOOutput(GPIO_PORTD_BASE, GPIO_PIN_6 | GPIO_PIN_3);
	GPIOPinWrite(GPIO_PORTD_BASE, GPIO_PIN_6 | GPIO_PIN_3, 0xFF);

	SSIEnable(SSI0_BASE);
	
       //get rid of old data in fifo
	unsigned long junk;
	GPIOPinWrite(GPIO_PORTD_BASE, GPIO_PIN_6, 0x00);	//select device
	do {
		SSIDataPut(SSI0_BASE, 143);
	}
	while(SSIDataGetNonBlocking(SSI0_BASE, &junk));
	GPIOPinWrite(GPIO_PORTD_BASE, GPIO_PIN_6, 0xff);	//deselect device
}

int SPI_x() {

	SysCtlDelay(1000);    
	unsigned long who_am_i_value;
	GPIOPinWrite(GPIO_PORTD_BASE, GPIO_PIN_6, 0x00);    //start comunication
	SSIDataPut(SSI0_BASE, 143);
	SSIDataGet(SSI0_BASE, &who_am_i_value);
	SysCtlDelay(10000);    
	GPIOPinWrite(GPIO_PORTD_BASE, GPIO_PIN_6, 0xff);    //staph comunication
	return who_am_i_value;
}

over 10 years ago

0 Luis Afonso over 10 years ago

Guru 20670 points

Not to be rude but the Stellaris forum is in here:
e2e.ti.com/.../stellaris_arm

You are in the Tiva forum.

Anyway, you have it now the CS connected to PD6. You did try to connect it to PA3 prior to using the GPIO method?

Do you have a scope to monitor the signals?

0 Amit Ashara over 10 years ago

TI__Guru**** 244400 points

Hello Bartosz,

I think the issue is in the code here. To get rid of the data the whole code needs to be replaced from

//get rid of old data in fifo
unsigned long junk;
GPIOPinWrite(GPIO_PORTD_BASE, GPIO_PIN_6, 0x00); //select device
do {
SSIDataPut(SSI0_BASE, 143);
}
while(SSIDataGetNonBlocking(SSI0_BASE, &junk));
GPIOPinWrite(GPIO_PORTD_BASE, GPIO_PIN_6, 0xff); //deselect device

to

while(SSIDataGetNonBlocking(SSI0_BASE, &junk));

The reason is because any old data needs to be flushed before any new data is to be read out. By doing the CS stuff, you are making the slave respond to the data.

Regards
Amit

0 Bartosz Szmit over 10 years ago

Prodigy 30 points

Thanks for reply.

I have connected CS to A3 pin, but problem had still existed.

Currently I do not have any scope, but I am going to buy Logic Analyzer .

I have have changed code as Amit suggested.
My problem has changed. Now I am receaving value, that I send as an address. As example: I send address 143, and I receive 143 value.
I tried doing "dummy send" ( according to LSM9DS0 datasheet [page 35], during SPI read, MOSI line isn't empty).
SSIDataPut(SSI0_BASE, 143);
SSIDataPut(SSI0_BASE, 142);
SSIDataGet(SSI0_BASE, &who_am_i_value);

Then I get
143
142
143
142, etc.

What could be an issue?

PS.
My bad about wrong forum ;)
If you dont mind, I will not change it. As far as I know Stellaris and Tiva are very similar for Cortex M4f.

0 Amit Ashara over 10 years ago in reply to Bartosz Szmit

TI__Guru**** 244400 points

Hello Bartosz,

When working with Legacy mode one important thing is that for every SSIDataPut a SSIDataGet is required. The last code post does not show that. Perhaps having the corrected code for review shall be more helpful before the LA comes.

Regards
Amit

0 Bartosz Szmit over 10 years ago in reply to Amit Ashara

Prodigy 30 points

Ok, I have finally solve this.

This was a hardware problem. I powered LM4F120XL and LSM9DS0 from independent power sources (both 3.3V). Howewer I did not connect their grounds together. And that was causing all these problems.

After connecting their grounds together everything works great.

Also, in software, I have to do double put (and double get like Amit suggested).

My code:

void SPIInit() {
	SysCtlClockSet(SYSCTL_SYSDIV_1 | SYSCTL_USE_OSC | SYSCTL_OSC_MAIN |
	                   SYSCTL_XTAL_8MHZ);
	SysCtlPeripheralEnable(SYSCTL_PERIPH_SSI0);
	SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOA);
	GPIOPinConfigure(GPIO_PA2_SSI0CLK);
	GPIOPinConfigure(GPIO_PA3_SSI0FSS);
	GPIOPinConfigure(GPIO_PA4_SSI0RX);
	GPIOPinConfigure(GPIO_PA5_SSI0TX);
	GPIOPinTypeSSI(GPIO_PORTA_BASE, GPIO_PIN_5 | GPIO_PIN_4 | GPIO_PIN_3 |
	GPIO_PIN_2);

	SSIConfigSetExpClk(SSI0_BASE, SysCtlClockGet() , SSI_FRF_MOTO_MODE_3,
	SSI_MODE_MASTER, 100000, 8);

	//cs pin
	SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOD);
	GPIOPinTypeGPIOOutput(GPIO_PORTD_BASE, GPIO_PIN_6);
	GPIOPinWrite(GPIO_PORTD_BASE, GPIO_PIN_6 , 0xFF);

	SSIEnable(SSI0_BASE);

	unsigned long junk;
	while(SSIDataGetNonBlocking(SSI0_BASE, &junk));


}

int SPI_x() {

	SysCtlDelay(1000);    
	unsigned long who_am_i_value = 187;
	GPIOPinWrite(GPIO_PORTD_BASE, GPIO_PIN_6, 0x00);    //start comunication
	SysCtlDelay(10000);  
	SSIDataPut(SSI0_BASE, 143);
	SSIDataPut(SSI0_BASE, 143);                           //DOUBLE PUT
	SSIDataGet(SSI0_BASE, &who_am_i_value);   //DOUBLE GET
	SSIDataGet(SSI0_BASE, &who_am_i_value);
	SysCtlDelay(10000);  
	GPIOPinWrite(GPIO_PORTD_BASE, GPIO_PIN_6, 0xff);    //stop comunication
	return who_am_i_value;
}

Thanks for all help!

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lm4f120xl - SPI problem