SPI slave driver speed problem

Hi Dialog,

I am developing a SPI slave driver for DA14580, however, I could run it up to 250KHz. Could you guys give me some suggestion on how to make it faster? Thanks a lot.

Init function:

// Initialize SPI module
SetBits16(SPI_CTRL_REG,SPI_ON,0); // Close SPI module, if opened
SetBits16(SPI_CTRL_REG,SPI_WORD,0); // Set to 8-bit mode
SetBits16(SPI_CTRL_REG,SPI_SMN, 0x01); // Set SPI in SLAVE mode
SetBits16(SPI_CTRL_REG,SPI_POL, 0x0); // Mode 3: SPI_POL = 0
SetBits16(SPI_CTRL_REG,SPI_PHA, 0x0); // and SPI_PHA = 0
SetBits16(SPI_CTRL_REG,SPI_MINT, 0x1); // Enable SPI Maskable Interrupt to CPU
SetBits16(SPI_CTRL_REG1,SPI_FIFO_MODE,0x00); // Enable SPI RX and TX FIFOs
SetBits16 (SPI_CTRL_REG SPI_EN_CTRL 1);/ /启用年代PI EN pin for slave mode
SetBits16(SPI_CTRL_REG,SPI_ON,1); // Enable SPI module

// Configure SPI environment
NVIC_ClearPendingIRQ(SPI_IRQn);
NVIC_SetPriority(SPI_IRQn,0);
NVIC_EnableIRQ(SPI_IRQn);

In ISR:
void SPI_Handler(void)
{
static uint8_t data;
// Wait until data is ready
while (0xFF&GetBits16(SPI_CTRL_REG,SPI_INT_BIT) == 1)
{
data = 0xFF&GetWord16(SPI_RX_TX_REG0);
while ((GetBits16(SPI_CTRL_REG,SPI_TXH)==1)||(GetBits16(SPI_CTRL_REG1,SPI_BUSY)==1));
SetWord16(SPI_RX_TX_REG0, 0xFF&data);
SetWord16(SPI_CLEAR_INT_REG, 0x01);
}

}