Hello Guys
I am building a very simple application using CubeMX.
I am using two STM32F207ZG boards to communicate with each other over SPI bus without DMA or interrupts.
One is acting as a master another as as slave.
The slave settings are as follows.
hspi1.Instance = SPI1;
hspi1.Init.Mode = SPI_MODE_SLAVE;
hspi1.Init.Direction = SPI_DIRECTION_2LINES;
hspi1.Init.DataSize = SPI_DATASIZE_8BIT;
hspi1.Init.CLKPolarity = SPI_POLARITY_LOW;
hspi1.Init.CLKPhase = SPI_PHASE_1EDGE;
hspi1.Init.NSS = SPI_NSS_SOFT;
hspi1.Init.BaudRatePrescaler = SPI_BAUDRATEPRESCALER_4;
hspi1.Init.FirstBit = SPI_FIRSTBIT_MSB;
hspi1.Init.TIMode = SPI_TIMODE_DISABLE;
hspi1.Init.CRCCalculation = SPI_CRCCALCULATION_DISABLE;
hspi1.Init.CRCPolynomial = 10;
The problem is i don't want to use NSS pin in hardware mode as it is being used for other purpose. If i configure NSS to be as software, i am missing one clock edge coming from the master and the slave is always stuck checking the TXE bit at the end of transmission inside HAL_SPI_TransmitReceive(....) function (because it is waiting for one more clock edge). i have verified it by sending 0xAA series from the master and the slave always receive 0x55.
/* Wait until TXE flag */
if(SPI_WaitFlagStateUntilTimeout(hspi, SPI_FLAG_TXE, SET, Timeout, tickstart) != HAL_OK)
{
errorcode = HAL_TIMEOUT;
goto error;
}
But here if i reset the spi communication (i am resetting the controller), then surprisingly there after no problem in SPI communication.
Also if i put a CRO probe on the clock signal everything works fine.
I thought of capacitance issue but i have reduced the clock frequency to lowest possible but it didn't help, moreover i wonder if it would have been a problem with the capacitance why it would work after resetting the slave controller at the first place.
I would really appreciate if someone could please help me out of this issue.
Many thanks in advance. let me know if any other details are required
