# SPI Usage Guidelines - [How to Use](#section691514116412) - [Obtaining an SPI Device Handle](#section12372204616215) - [Obtaining SPI Device Configuration Parameters](#section17121446171311) - [Setting SPI Device Configuration Parameters](#section97691946634) - [Performing SPI Communication](#section197116254416) - [Destroying the SPI Device Handle](#section117661819108) ## How to Use [Figure 1](#fig23885455594) shows the process of using an SPI device. **Figure 1** Process of using an SPI device ![](figures/en-us_image_0000001054726248.png) ## Obtaining an SPI Device Handle Before performing SPI communication, obtain an SPI device handle by calling **SpiOpen**. This function returns an SPI device handle with a specified bus number and CS number. DevHandle SpiOpen\(const struct SpiDevInfo \*info\); **Table 1** Description of **SpiOpen**

Parameter	Description
info	Pointer to the SPI device descriptor.
Return Value	Description
NULL	Failed to obtain an SPI device handle.
Device handle	Returns the pointer to the SPI device handle.

The following example shows how to obtain an SPI device handle based on the assumption that both the bus number and CS number of the SPI device are **0**. ``` struct SpiDevInfo spiDevinfo; /* SPI device descriptor */ DevHandle spiHandle = NULL; /* SPI device handle */ spiDevinfo.busNum = 0; /* SPI device bus number */ spiDevinfo.csNum = 0; /* SPI device CS number */ /* Obtain an SPI device handle. */ spiHandle = SpiOpen(&spiDevinfo); if (spiHandle == NULL) { HDF_LOGE("SpiOpen: failed\n"); return; } ``` ## Obtaining SPI Device Configuration Parameters After obtaining the SPI device handle, obtain the SPI device configuration parameters by calling the following function: int32\_t SpiGetCfg\(DevHandle handle, struct SpiCfg \*cfg\); **Table 2** Description of **SpiGetCfg**

Parameter	Description
handle	Pointer to the SPI device handle.
cfg	Pointer to SPI device configuration parameters.
Return Value	Description
0	Succeeded in obtaining SPI device configuration parameters.
Negative value	Failed to obtain SPI device configuration parameters.

``` int32_t ret; struct SpiCfg cfg = {0}; /* SPI configuration information */ ret = PalSpiSetCfg(spiHandle, &cfg); /* Set SPI device configuration parameters. */ if (ret != 0) { HDF_LOGE("SpiGetCfg: failed, ret %d\n", ret); } ``` ## Setting SPI Device Configuration Parameters After obtaining the SPI device handle, set SPI device configuration parameters by calling the following function: int32\_t SpiSetCfg\(DevHandle handle, struct SpiCfg \*cfg\); **Table 3** Description of **SpiSetCfg**

Parameter	Description
handle	Pointer to the SPI device handle.
cfg	Pointer to SPI device configuration parameters.
Return Value	Description
0	Succeeded in setting SPI device configuration parameters.
Negative value	Failed to set SPI device configuration parameters.

``` int32_t ret; struct SpiCfg cfg = {0}; /* SPI configuration information */ cfg.mode = SPI_MODE_LOOP; /* Communicate in loopback mode. */ cfg.comMode = PAL_SPI_POLLING_TRANSFER; /* Communicate in polling mode. */ cfg.maxSpeedHz = 115200; /* Maximum transmission frequency */ cfg.bitsPerWord = 8; /* The width of per word to be read or written is 8 bits. */ ret = SpiSetCfg(spiHandle, &cfg); /* Set SPI device configuration parameters. */ if (ret != 0) { HDF_LOGE("SpiSetCfg: failed, ret %d\n", ret); } ``` ## Performing SPI Communication - Writing data of a specified length into an SPI device To write data into an SPI device only once, call the following function: int32\_t SpiWrite\(DevHandle handle, uint8\_t \*buf, uint32\_t len\); **Table 4** Description of **SpiWrite**

Parameter	Description
handle	Pointer to the SPI device handle.
buf	Pointer to the data to write.
len	Length of the data to write.
Return Value	Description
0	Succeeded in writing data into an SPI device.
Negative value	Failed to write data into an SPI device.

``` int32_t ret; uint8_t wbuff[4] = {0x12, 0x34, 0x56, 0x78}; /* Write data of a specified length into an SPI device. */ ret = SpiWrite(spiHandle, wbuff, 4); if (ret != 0) { HDF_LOGE("SpiWrite: failed, ret %d\n", ret); } ``` - Reading data of a specified length from an SPI device To read data from an SPI device only once, call the following function: int32\_t SpiRead\(DevHandle handle, uint8\_t \*buf, uint32\_t len\); **Table 5** Description of **SpiRead**

Parameter	Description
handle	Pointer to the SPI device handle.
buf	Pointer to the data to read.
len	Length of the data to read.
Return Value	Description
0	Succeeded in reading data from an SPI device.
Negative value	Failed to read data from an SPI device.

``` int32_t ret; uint8_t rbuff[4] = {0}; /* Read data of a specified length from an SPI device. */ ret = SpiRead(spiHandle, rbuff, 4); if (ret != 0) { HDF_LOGE("SpiRead: failed, ret %d\n", ret); } ``` - Launching a custom transfer To launch a custom transfer, call the following function: int32\_t SpiTransfer\(DevHandle handle, struct SpiMsg \*msgs, uint32\_t count\); **Table 6** Description of **SpiTransfer**

Parameter	Description
handle	Pointer to the SPI device handle.
msgs	Pointer to the message array to be transferred.
count	Length of the message array.
Return Value	Description
0	Succeeded in launching the custom transfer.
Negative value	Failed to launch the custom transfer.

``` int32_t ret; uint8_t wbuff[1] = {0x12}; uint8_t rbuff[1] = {0}; struct SpiMsg msg; /* Custom message to be transferred */ msg.wbuf = wbuff; /* Pointer to the data to read */ msg.rbuf = rbuff; /* Pointer to the data to read */ msg.len = 1; /* The length of the data to be read or written is 1 bit. */ msg.csChange = 1; /* Disable the CS before the next transfer. */ msg.delayUs = 0; /* No delay before the next transfer */ msg.speed = 115200; /* Speed of this transfer */ /* Launch a custom transfer. The number of messages to be transferred is 1. */ ret = SpiTransfer(spiHandle, &msg, 1); if (ret != 0) { HDF_LOGE("SpiTransfer: failed, ret %d\n", ret); } ``` ## Destroying the SPI Device Handle After the SPI communication, destroy the SPI device handle by calling the following function: void SpiClose\(DevHandle handle\); This function will release the resources previously obtained. **Table 7** Description of **SpiClose**

Parameter	Description
handle	Pointer to the SPI device handle

``` PalHandleDestroy(spiHandle); /* Destroy the SPI device handle. */ ```