TM4C123GH6PGE: SSI/SPI於工作期間CLK及IO輸出波形問題

SPI 时钟的最大规格为 25MHz。 20Mhz 没啥问题，您的波形也正常。

同时请您确保主器件和从器件配置为完全相同的 SPICLK 相位和极性，为从机提供半周期的设置时间以进行数据采样。 SSI 引脚的默认驱动强度为 2mA， 请参阅以下内容。 建议您设置更高的驱动强度，修改到比如4mA，然后看下有没有什么改善。以及请您手动配置端口，不要使用 TivaWare Library。

//*****************************************************************************
//
//! Configures pin(s) for use by the SSI peripheral.
//!
//! \param ui32Port is the base address of the GPIO port.
//! \param ui8Pins is the bit-packed representation of the pin(s).
//!
//! The SSI pins must be properly configured for the SSI peripheral to function
//! correctly. This function provides a typical configuration for those
//! pin(s); other configurations may work as well depending upon the board
//! setup (for example, using the on-chip pull-ups).
//!
//! The pin(s) are specified using a bit-packed byte, where each bit that is
//! set identifies the pin to be accessed, and where bit 0 of the byte
//! represents GPIO port pin 0, bit 1 represents GPIO port pin 1, and so on.
//!
//! \note This function cannot be used to turn any pin into a SSI pin; it only
//! configures a SSI pin for proper operation. Note that a GPIOPinConfigure()
//! function call is also required to properly configure a pin for the SSI
//! function.
//!
//! \note A subset of GPIO pins on Tiva devices, notably those used by the
//! JTAG/SWD interface and any pin capable of acting as an NMI input, are
//! locked against inadvertent reconfiguration. These pins must be unlocked
//! using direct register writes to the relevant GPIO_O_LOCK and GPIO_O_CR
//! registers before this function can be called. Please see the ``gpio_jtag''
//! example application for the mechanism required and consult your part
//! datasheet for information on affected pins.
//!
//! \return None.
//
//*****************************************************************************

void
GPIOPinTypeSSI(uint32_t ui32Port, uint8_t ui8Pins)
{
//
// Check the arguments.
//
ASSERT(_GPIOBaseValid(ui32Port));

//
// Make the pin(s) be peripheral controlled.
//
GPIODirModeSet(ui32Port, ui8Pins, GPIO_DIR_MODE_HW);

//
// Set the pad(s) for standard push-pull operation.
//
GPIOPadConfigSet(ui32Port, ui8Pins, GPIO_STRENGTH_2MA, GPIO_PIN_TYPE_STD);

您好，详细信息请您参阅数据表。 如您所说当连续传输时，两次传输之间将有一些空闲。 请参阅数据表中的下图：

同时请参考以下信息：（英文描述对您来说ok吗？这是数据表中的信息，如果您理解有难度的话请告知我）

In the case of a single word transmission, after all bits of the data word have been transferred, the
SSInFss line is returned to its idle High state one SSInClk period after the last bit has been
captured.
However, in the case of continuous back-to-back transmissions, the SSInFss signal must be pulsed
High between each data word transfer because the slave select pin freezes the data in its serial
peripheral register and does not allow it to be altered if the SPH bit is clear. Therefore, the master
device must raise the SSInFss pin of the slave device between each data transfer to enable the
serial peripheral data write. On completion of the continuous transfer, the SSInFss pin is returned
to its idle state one SSInClk period after the last bit has been captured.