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Why F030C8 SPI performes like this? "Data packing“ problem

Question asked by ze.ala on Jan 8, 2016
Latest reply on Jan 10, 2016 by ze.ala
IDE environment: KEIL v5.14 + CubeMX v4.12 + CubeF0 v1.4
Chip type:F030C8T6
Debugger:ST-LINK VII

When I use SPI in polling mode, i found a weird thing. I have never met this before when I were using F1xx series chips.

The date size is set to 8-bit long and MSB first (SPIx_CR1=0x36C,SPIx_CR2=0x1700).

Here is the main code.

while(1)
{
     SPI1->DR = 0XFF;
     while(SPI1->SR & SPI_SR_BSY);
     while(!(SPI1->SR & SPI_SR_RXNE));
     temp = SPI1->DR;
}


This is the corresponding waveform.
0X00FF.BMP

Is the sentence "SPI1->DR = 0XFF;" a kind of "16-bit access of SPIx_DR"?
When I replaced 0XFF with a uint8_t variable the waveform didn't change at all.
I also changed the optimization level to -O0, but it had no effect.

"Data packing" is too inconvenient to communicate with some devices,like nRF24L01. Can anyone tell me how to read/write SPIx_DR in a 8-bit way like it is in F1xx series? 

Thanks.

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