UART Usage Guidelines

• How to Use
• Obtaining a UART Device Handle
• Setting the UART Baud Rate
• Obtaining the UART Baud Rate
• Setting the UART Device Attributes
• Obtaining UART Device Attributes
• Setting the UART Transmission Mode
• Writing Data of a Specified Length into a UART Device
• Reading Data of a Specified Length from a UART Device
• Destroying the UART Device Handle

How to Use

Figure 1 shows the process of using a UART device.

Figure 1 Process of using a UART device

Obtaining a UART Device Handle

Before performing UART communication, call UartOpen to obtain a UART device handle. This function returns the pointer to the UART device handle with a specified port number.

DevHandle UartOpen(uint32_t port);

Table 1 Description of UartOpen

The following example shows how to obtain a UART device handle based on the assumption that the UART port number is 3:

DevHandle handle = NULL;    /* The UART device handle */
uint32_t port = 3;                  /* UART port number */
handle = UartOpen(port);
if (handle == NULL) {
    HDF_LOGE("UartOpen: failed!\n");
    return;
}

Setting the UART Baud Rate

After obtaining the UART device handle, set the UART baud rate by calling the following function:

int32_t UartSetBaud(DevHandle handle, uint32_t baudRate);

Table 2 Description of UartSetBaud

The following example shows how to set the UART baud rate to 9600:

int32_t ret;
/* Set the UART baud rate to 9600. */
ret = UartSetBaud(handle, 9600);
if (ret != 0) {
    HDF_LOGE("UartSetBaud: failed, ret %d\n", ret);
}

Obtaining the UART Baud Rate

After setting the UART baud rate, obtain the current baud rate by calling the following function:

int32_t UartGetBaud(DevHandle handle, uint32_t *baudRate);

Table 3 Description of UartGetBaud

The following example shows how to obtain the UART baud rate:

int32_t ret;
uint32_t baudRate;
/* Obtain the UART baud rate. */
ret = UartGetBaud(handle, &baudRate);
if (ret != 0) {
    HDF_LOGE("UartGetBaud: failed, ret %d\n", ret);
}

Setting the UART Device Attributes

Before performing UART communication, set the UART device attributes by calling the following function:

int32_t UartSetAttribute(DevHandle handle, struct UartAttribute *attribute);

Table 4 Description of UartSetAttribute

The following example shows how to set the UART device attributes:

int32_t ret;
struct UartAttribute attribute;
attribute.dataBits = UART_ATTR_DATABIT_7;   /* Set the number of data bits to 7. */
attribute.parity = UART_ATTR_PARITY_NONE;   /* Set the parity bit to no parity. */
attribute.stopBits = UART_ATTR_STOPBIT_1;   /* Set the stop bit to 1. */
attribute.rts = UART_ATTR_RTS_DIS;          /* Disable the RTS signal. */
attribute.cts = UART_ATTR_CTS_DIS;          /* Disable the CTS signal. */
attribute.fifoRxEn = UART_ATTR_RX_FIFO_EN;  /* Enable RX FIFO. */
attribute.fifoTxEn = UART_ATTR_TX_FIFO_EN;  /* Enable TX FIFO. */
/* Set the UART device attributes. */
ret = UartSetAttribute(handle, &attribute);
if (ret != 0) {
    HDF_LOGE("UartSetAttribute: failed, ret %d\n", ret);
}

Obtaining UART Device Attributes

After setting the UART device attributes, obtain the current device attributes by calling the following function:

int32_t UartGetAttribute(DevHandle handle, struct UartAttribute *attribute);

Table 5 Description of UartGetAttribute

The following example shows how to obtain the UART device attributes:

int32_t ret;
struct UartAttribute attribute;
/* Obtain the UART attributes. */
ret = UartGetAttribute(handle, &attribute);
if (ret != 0) {
    HDF_LOGE("UartGetAttribute: failed, ret %d\n", ret);
}

Setting the UART Transmission Mode

Before performing UART communication, set the UART transmission mode by calling the following function:

int32_t UartSetTransMode(DevHandle handle, enum UartTransMode mode);

Table 6 Description of UartSetTransMode

The following example shows how to set the transmission mode to UART_MODE_RD_BLOCK:

int32_t ret;
/* Set the UART transmission mode. */
ret = UartSetTransMode(handle, UART_MODE_RD_BLOCK);
if (ret != 0) {
    HDF_LOGE("UartSetTransMode: failed, ret %d\n", ret);
}

Writing Data of a Specified Length into a UART Device

To write data into a UART device, call the following function:

int32_t UartWrite(DevHandle handle, uint8_t *data, uint32_t size);

Table 7 Description of UartWrite

The following example shows how to write data of a specified length into the UART device:

int32_t ret;
uint8_t wbuff[5] = {1, 2, 3, 4, 5};
/* Write 5-byte data into the UART device. */
ret = UartWrite(handle, wbuff, 5);
if (ret != 0) {
    HDF_LOGE("UartWrite: failed, ret %d\n", ret);
}

Reading Data of a Specified Length from a UART Device

To read data from a UART device, call the following function:

int32_t UartRead(DevHandle handle, uint8_t *data, uint32_t size);

Table 8 Description of UartRead

The following example shows how to read data of a specified length from the UART device:

int32_t ret;
uint8_t rbuff[5] = {0};
/* Read 5-byte data from the UART device. */
ret = UartRead(handle, rbuff, 5);
if (ret < 0) {
    HDF_LOGE("UartRead: failed, ret %d\n", ret);
}

CAUTION: Data is successfully read from the UART device if a non-negative value is returned. If the return value is 0, no valid data can be read from the UART device. If the return value is greater than 0, the return value is the length of the data actually read from the UART device. The length is less than or equal to the value of size and does not exceed the maximum length of data to read at a time specified by the UART controller in use.

Destroying the UART Device Handle

After the UART communication, destroy the UART device handle by calling the following function:

void UartClose(DevHandle handle);

This function will release the resources previously obtained.

Table 9 Description of UartClose

The following example shows how to destroy the UART device handle:

UartClose(handle); /* Destroy the UART device handle. */