Hi,
How do we configure the SSI to high impedance?
We are connecting a QSPI flash between the MCU and a FPGA.
This QSPI flash is shared by the MCU and FPGA through SPI.
MCU SSI will be required to be high impedance state when the FPGA is accessing the flash.
Thank you.
Here is a routine that sends some data out the SSI, then turns the pins into GPIO inputs. Finally, the pins are configured with pull-ups so you can see the effect in the logic analyzer picture.
#include <stdint.h>
#include <stdbool.h>
#include "inc/hw_types.h"
#include "inc/hw_memmap.h"
#include "driverlib/sysctl.h"
#include "driverlib/gpio.h"
#include "driverlib/ssi.h"
#include "driverlib/pin_map.h"
unsigned char u8DataTx[4] = {'A','B','C','D'};
unsigned char u8DataRx[4];
int
main(void)
{
uint32_t ui32Index, ui32DataPut, ui32DataGet;
SysCtlClockSet(SYSCTL_SYSDIV_1 | SYSCTL_USE_OSC | SYSCTL_OSC_MAIN |
SYSCTL_XTAL_16MHZ);
// The SSI2 peripheral must be enabled for use.
SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOB);
SysCtlPeripheralEnable(SYSCTL_PERIPH_SSI2);
GPIOPinConfigure(GPIO_PB4_SSI2CLK);
GPIOPinConfigure(GPIO_PB5_SSI2FSS);
GPIOPinConfigure(GPIO_PB6_SSI2RX);
GPIOPinConfigure(GPIO_PB7_SSI2TX);
GPIOPinTypeSSI(GPIO_PORTB_BASE, GPIO_PIN_4 | GPIO_PIN_5 | GPIO_PIN_6 | GPIO_PIN_7);
SSIConfigSetExpClk(SSI2_BASE, SysCtlClockGet(), SSI_FRF_MOTO_MODE_0,
SSI_MODE_MASTER, 1000000, 8);
SSIEnable(SSI2_BASE);
//
// Send n bytes of data.
//
for(ui32Index = 0; ui32Index < 4; ui32Index++)
{
ui32DataPut = (uint32_t)u8DataTx[ui32Index];
SSIDataPut(SSI2_BASE, ui32DataPut);
SSIDataGet(SSI2_BASE, &ui32DataGet);
u8DataRx[ui32Index] = (uint8_t)ui32DataGet;
}
// Now configure the SPI pins as digital inputs
GPIOPinTypeGPIOInput(GPIO_PORTB_BASE, GPIO_PIN_4 | GPIO_PIN_5 | GPIO_PIN_6 | GPIO_PIN_7);
// Configure with pull-ups
GPIOPadConfigSet(GPIO_PORTB_BASE, GPIO_PIN_4 | GPIO_PIN_5 | GPIO_PIN_6 | GPIO_PIN_7,
GPIO_STRENGTH_2MA, GPIO_PIN_TYPE_STD_WPU);
}
