SPI Usage Guidelines
- How to Use
- Obtaining an SPI Device Handle
- Obtaining SPI Device Configuration Parameters
- Setting SPI Device Configuration Parameters
- Performing SPI Communication
- Destroying the SPI Device Handle
How to Use
Figure 1 shows the process of using an SPI device.
Figure 1 Process of using an SPI device
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
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
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
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
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
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
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
PalHandleDestroy(spiHandle); /* Destroy the SPI device handle. */