69.6.2. Use DMA to receive and send UART data

69.6.2.1. Overview

In this example project, UART receives/sends data via DMA.

69.6.2.2. Port Settings

• Serial port baud rate is set to 115200bps , with one stop bit and no parity bit

69.6.2.3. Configuration

• Enable FIFO mode and set FIFO thresholds. Enable DMA via dma_enable and fifo_enable in uart_config_t structure.

  • DMA request triggers when: - RX FIFO data exceeds threshold - TX FIFO free space exceeds threshold

  • Two FIFO threshold width modes (defined in uart_fifo_trg_lvl_t from hpm_uart_drv.h):

    • 2-bit width thresholds (0-3):

      • TX FIFO Thresholds:

        Enum	16-byte FIFO	32-byte FIFO
        uart_tx_fifo_trg_not_full	Not full	Not full
        uart_tx_fifo_trg_lt_three_quarters	<12 bytes	<24 bytes
        uart_tx_fifo_trg_lt_half	<8 bytes	<16 bytes
        uart_tx_fifo_trg_lt_one_quarter	<4 bytes	<8 bytes

      • RX FIFO Thresholds:

        Enum	16-byte FIFO	32-byte FIFO
        uart_rx_fifo_trg_not_empty	Not empty	Not empty
        uart_rx_fifo_trg_gt_one_quarter	>3 bytes	>7 bytes
        uart_rx_fifo_trg_gt_half	>7 bytes	>15 bytes
        uart_rx_fifo_trg_gt_three_quarters	>13 bytes	>27 bytes

      • Examples: - tx_fifo_level = uart_tx_fifo_trg_lt_half: Triggers DMA when TX FIFO <8 bytes (16-byte FIFO) - rx_fifo_level = uart_rx_fifo_trg_gt_one_quarter: Triggers DMA when RX FIFO >3 bytes (16-byte FIFO)

    • 4-bit width thresholds (0-31) for 1-32 byte granularity: - Requires HPM_IP_FEATURE_UART_FINE_FIFO_THRLD in hpm_soc_ip_feature.h

      • Examples: - tx_fifo_level = 15: Triggers DMA when TX FIFO <= 15 bytes (32-byte FIFO) - rx_fifo_level = 27: Triggers DMA when RX FIFO >= 27 bytes (32-byte FIFO)

• Note:

  • RX FIFO timeout will trigger DMA request even when FIFO data below threshold

  • To disable timeout-triggered DMA when below threshold: - Use uart_disable_rx_timeout_trig_dma API - Requires SOC support via HPM_IP_FEATURE_UART_DISABLE_DMA_TIMEOUT in hpm_soc_ip_feature.h - Default configuration: RX FIFO timeout DMA trigger disabled

69.6.2.4. Note

• The input string length should not exceed TEST_BUFF_SIZE defined in the program every time

69.6.2.5. Running the example

When the project runs correctly, manually input the char through the serial port, such as ‘1234567887654321’, and the serial port terminal will receive the following information:

UART DMA example
UART will send back received characters, echo every 16 bytes
1234567887654321