请问如何使用TMS320F28027发送8位SPI数据

测试程序中是16位的,也就是说
SPI_setCharLength(mySpi, SPI_CharLength_16_Bits);
我把他改成8位,
  SPI_setCharLength(mySpi, SPI_CharLength_8_Bits);
然后数据发送
SPI_write(mySpi, 0xAA);
结果什么都没有发送,为什么呢.
完整代码.
#include "DSP28x_Project.h"
#include "f2802x_common/include/adc.h"
#include "f2802x_common/include/clk.h"
#include "f2802x_common/include/flash.h"
#include "f2802x_common/include/gpio.h"
#include "f2802x_common/include/pie.h"
#include "f2802x_common/include/pll.h"
#include "f2802x_common/include/spi.h"
#include "f2802x_common/include/wdog.h"
void delay_loop(void);
void spi_xmit(uint16_t a);
void spi_fifo_init(void);
void spi_init(void);
void error(void);
ADC_Handle myAdc;
CLK_Handle myClk;
FLASH_Handle myFlash;
GPIO_Handle myGpio;
PIE_Handle myPie;
SPI_Handle mySpi;
void main(void)
[
CPU_Handle myCpu;
PLL_Handle myPll;
WDOG_Handle myWDog;
// Initialize all the handles needed for this application
myAdc = ADC_init((void *)ADC_BASE_ADDR, sizeof(ADC_Obj));
myClk = CLK_init((void *)CLK_BASE_ADDR, sizeof(CLK_Obj));
myCpu = CPU_init((void *)NULL, sizeof(CPU_Obj));
myFlash = FLASH_init((void *)FLASH_BASE_ADDR, sizeof(FLASH_Obj));
myGpio = GPIO_init((void *)GPIO_BASE_ADDR, sizeof(GPIO_Obj));
myPie = PIE_init((void *)PIE_BASE_ADDR, sizeof(PIE_Obj));
myPll = PLL_init((void *)PLL_BASE_ADDR, sizeof(PLL_Obj));
mySpi = SPI_init((void *)SPIA_BASE_ADDR, sizeof(SPI_Obj));
myWDog = WDOG_init((void *)WDOG_BASE_ADDR, sizeof(WDOG_Obj));
// 初始化
WDOG_disable(myWDog);
CLK_enableAdcClock(myClk);
(*Device_cal)();

CLK_setOscSrc(myClk, CLK_OscSrc_Internal);
PLL_setup(myPll, PLL_Multiplier_10, PLL_DivideSelect_ClkIn_by_2);
PIE_disable(myPie);
PIE_disableAllInts(myPie);
CPU_disableGlobalInts(myCpu);
CPU_clearIntFlags(myCpu);

#ifdef _FLASH
memcpy(&RamfuncsRunStart, &RamfuncsLoadStart, (size_t)&RamfuncsLoadSize);
#endif
// Initalize GPIO
GPIO_setPullUp(myGpio, GPIO_Number_16, GPIO_PullUp_Enable);
GPIO_setPullUp(myGpio, GPIO_Number_17, GPIO_PullUp_Enable);
GPIO_setPullUp(myGpio, GPIO_Number_18, GPIO_PullUp_Enable);
GPIO_setPullUp(myGpio, GPIO_Number_19, GPIO_PullUp_Enable);
GPIO_setQualification(myGpio, GPIO_Number_16, GPIO_Qual_ASync);
GPIO_setQualification(myGpio, GPIO_Number_17, GPIO_Qual_ASync);
GPIO_setQualification(myGpio, GPIO_Number_18, GPIO_Qual_ASync);
GPIO_setQualification(myGpio, GPIO_Number_19, GPIO_Qual_ASync);
GPIO_setMode(myGpio, GPIO_Number_16, GPIO_16_Mode_SPISIMOA);
GPIO_setMode(myGpio, GPIO_Number_17, GPIO_17_Mode_SPISOMIA);
GPIO_setMode(myGpio, GPIO_Number_18, GPIO_18_Mode_SPICLKA);
GPIO_setMode(myGpio, GPIO_Number_19, GPIO_19_Mode_SPISTEA_NOT);
PIE_setDebugIntVectorTable(myPie);
PIE_enable(myPie);
spi_init();
spi_fifo_init();
for(;;)
[

SPI_write(mySpi, 0xAA);

while(SPI_getRxFifoStatus(mySpi) == SPI_FifoStatus_Empty)
[
]
SPI_read(mySpi);

]
]

void delay_loop()
[
long i;
for (i = 0; i < 1000000; i++)
[
]
return;
]
void error(void)
[
asm(" ESTOP0"); // Test failed!! Stop!
for (;;)
[
]
]
void spi_init()
[
CLK_enableSpiaClock(myClk);
// Reset on, rising edge, 16-bit char bits
SPI_setCharLength(mySpi, SPI_CharLength_8_Bits);
// Enable master mode, normal phase,
// enable talk, and SPI int disabled.
SPI_setMode(mySpi, SPI_Mode_Master);
SPI_enableTx(mySpi);
SPI_setBaudRate(mySpi, SPI_BaudRate_500_KBaud);
// Relinquish SPI from Reset
//SPI_enableLoopBack(mySpi); //测试时候有用,环回测试.
SPI_enable(mySpi);
// Set so breakpoints don't disturb xmission
//优先级控制
/*
* 模式2:FreeRun:忽略中断
* 模式1:AfterRxRxSeq:
* 模式0:Immediate:
*/
SPI_setPriority(mySpi, SPI_Priority_FreeRun);
return;
]
void spi_fifo_init()
[
// Initialize SPI FIFO registers
SPI_enableChannels(mySpi);
SPI_enableFifoEnh(mySpi);
SPI_resetTxFifo(mySpi);
SPI_clearTxFifoInt(mySpi);
SPI_resetRxFifo(mySpi);
SPI_clearRxFifoInt(mySpi);
SPI_setRxFifoIntLevel(mySpi, SPI_FifoLevel_4_Words);
return;
]