STM32 F4/F7/H7开发板，使用SPI2做自收发实验，将PB14、PB15（MISO和MOSI）两个引脚连接，进行数据传输。
传输时发现，当数据总长度不超过16个字节时收发正常，超过16个字节接收到的数据全是0，请问是什么情况。。

附代码如下：
#define DATA_NUM 9
void SPI_Init(void)
{
        int i = 0;
        uint16_t tx[DATA_NUM] = {0x1234, 0x2234, 0x3234, 0x4234, 0x5234, 0x6234, 0x7234, 0x8234, 0x9234};//, 0xa234};
        uint16_t rx[DATA_NUM] = {0};
        SPI_HandleTypeDef SPI_Handler;
        SPI_Handler.Instance = SPI2;
        SPI_Handler.Init.Mode = SPI_MODE_MASTER;
        SPI_Handler.Init.Direction = SPI_DIRECTION_2LINES;
        SPI_Handler.Init.DataSize = SPI_DATASIZE_16BIT;
        SPI_Handler.Init.CLKPolarity = SPI_POLARITY_HIGH;
        SPI_Handler.Init.CLKPhase = SPI_PHASE_1EDGE;
        SPI_Handler.Init.NSS = SPI_NSS_SOFT;
        SPI_Handler.Init.BaudRatePrescaler = SPI_BAUDRATEPRESCALER_256;
        SPI_Handler.Init.FirstBit = SPI_FIRSTBIT_MSB;
        SPI_Handler.Init.TIMode = SPI_TIMODE_DISABLE;
        SPI_Handler.Init.CRCCalculation = SPI_CRCCALCULATION_DISABLE;
        SPI_Handler.Init.CRCPolynomial = 7;
        HAL_SPI_Init(&SPI_Handler);
        __HAL_SPI_ENABLE(&SPI_Handler);
        HAL_SPI_TransmitReceive(&SPI_Handler, (uint8_t *)tx, (uint8_t *)rx, sizeof(uint16_t) * DATA_NUM, 1000);
        for(i = 0; i < DATA_NUM; i++)
                printf("rx[%d] = %x ",i, rx[i]);
}