Add an example of using using DMA with PIO

README.md

@@ -305,6 +305,7 @@ App|Description
 [uart_tx](pio/uart_tx) | Implement the transmit component of a UART serial port, and print hello world.
 [ws2812](pio/ws2812) | Examples of driving WS2812 addressable RGB LEDs.
 [addition](pio/addition) | Add two integers together using PIO. Only around 8 billion times slower than Cortex-M0+.
+[uart_pio_dma](pio/uart_pio_dma) | Send and receive data from a UART implemented using the PIO and DMA
 
 ### PWM
 

pio/CMakeLists.txt

@@ -20,6 +20,7 @@ if (TARGET hardware_pio)
     add_subdirectory_exclude_platforms(uart_rx)
     add_subdirectory_exclude_platforms(uart_tx)
     add_subdirectory_exclude_platforms(ws2812)
+    add_subdirectory_exclude_platforms(uart_pio_dma)
 else()
     message("Skipping PIO examples as hardware_pio is unavailable on this platform")
 endif()

pio/uart_pio_dma/CMakeLists.txt

@@ -0,0 +1,11 @@
+add_executable(uart_pio_dma)
+pico_generate_pio_header(uart_pio_dma ${CMAKE_CURRENT_LIST_DIR}/../uart_rx/uart_rx.pio)
+pico_generate_pio_header(uart_pio_dma ${CMAKE_CURRENT_LIST_DIR}/../uart_tx/uart_tx.pio)
+target_sources(uart_pio_dma PRIVATE uart_pio_dma.c)
+target_link_libraries(uart_pio_dma PRIVATE
+        pico_stdlib
+        hardware_pio
+        hardware_dma
+        )
+pico_add_extra_outputs(uart_pio_dma)
+example_auto_set_url(uart_pio_dma)

pio/uart_pio_dma/uart_pio_dma.c

@@ -0,0 +1,269 @@
+/**
+ * Copyright (c) 2024 Raspberry Pi (Trading) Ltd.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <stdio.h>
+#include <string.h>
+
+#include "pico/stdlib.h"
+#include "hardware/pio.h"
+#include "hardware/uart.h"
+#include "hardware/dma.h"
+#include "uart_rx.pio.h"
+#include "uart_tx.pio.h"
+
+// Sends data via GPIO 4 and receives it on GPIO 5
+// Connect these pins with a wire
+#define GPIO_TX 4
+#define GPIO_RX 5
+
+#define SERIAL_BAUD 921600
+#define HARD_UART_INST uart1
+
+#define USE_PIO_FOR_RX 1
+#define USE_DMA_FOR_RX 1
+#define USE_PIO_FOR_TX 1
+#define USE_DMA_FOR_TX 1
+
+#ifndef DMA_IRQ_PRIORITY
+#define DMA_IRQ_PRIORITY PICO_SHARED_IRQ_HANDLER_DEFAULT_ORDER_PRIORITY
+#endif
+
+#ifndef PIO_IRQ_PRIORITY
+#define PIO_IRQ_PRIORITY PICO_SHARED_IRQ_HANDLER_DEFAULT_ORDER_PRIORITY
+#endif
+
+#define PIO_IRQ_TO_USE 0
+#define DMA_IRQ_TO_USE 0
+
+// dma channels
+static uint dma_channel_rx;
+static uint dma_channel_tx;
+
+// pio hardware
+#if USE_PIO_FOR_RX
+static PIO pio_hw_rx;
+static uint pio_sm_rx;
+static uint offset_rx;
+#endif
+
+#if USE_PIO_FOR_TX
+static PIO pio_hw_tx;
+static uint pio_sm_tx;
+static uint offset_tx;
+#endif
+
+// read request size for progress
+static uint32_t read_size;
+
+// PIO interrupt handler, called when the state machine fifo is not empty
+// note: shouldn't printf in an irq normally!
+static void pio_irq_handler() {
+    dma_channel_hw_t *dma_chan = dma_channel_hw_addr(dma_channel_rx);
+    printf("pio_rx dma_rx=%u/%u\n", read_size - dma_chan->transfer_count, read_size);
+}
+
+// DMA interrupt handler, called when a DMA channel has transmitted its data
+static void dma_irq_handler() {
+    if (dma_channel_tx >= 0 && dma_irqn_get_channel_status(DMA_IRQ_TO_USE, dma_channel_tx)) {
+        dma_irqn_acknowledge_channel(DMA_IRQ_TO_USE, dma_channel_tx);
+        printf("dma_tx done\n");
+    }
+    if (dma_channel_rx >= 0 && dma_irqn_get_channel_status(DMA_IRQ_TO_USE, dma_channel_rx)) {
+        dma_irqn_acknowledge_channel(DMA_IRQ_TO_USE, dma_channel_rx);
+        printf("dma_rx done\n");
+    }
+}
+
+static void dump_bytes(const char *bptr, uint32_t len) {
+    unsigned int i = 0;
+    for (i = 0; i < len;) {
+        if ((i & 0x0f) == 0) {
+            printf("\n");
+        } else if ((i & 0x07) == 0) {
+            printf(" ");
+        }
+        printf("%02x ", bptr[i++]);
+    }
+    printf("\n");
+}
+
+int main()
+{
+    setup_default_uart();
+
+    // setup text we are going to send and what we expect to get back
+    const char buffer_tx[] = "the quick brown fox jumps over the lazy dog";
+
+    // Buffer for receiving data
+    char buffer_rx[sizeof(buffer_tx) - 1] = {0};
+
+#if !USE_PIO_FOR_RX || !USE_PIO_FOR_TX
+    uart_init(HARD_UART_INST, SERIAL_BAUD);
+#endif
+
+// setup pio for rx
+#if USE_PIO_FOR_RX
+    if (!pio_claim_free_sm_and_add_program_for_gpio_range(&uart_rx_mini_program, &pio_hw_rx, &pio_sm_rx, &offset_rx, GPIO_RX, 1, true)) {
+        panic("failed to allocate pio for rx");
+    }
+    uart_rx_mini_program_init(pio_hw_rx, pio_sm_rx, offset_rx, GPIO_RX, SERIAL_BAUD);
+#else
+    gpio_set_function(GPIO_RX, GPIO_FUNC_UART);
+#endif
+
+// setup pio for tx
+#if USE_PIO_FOR_TX
+    if (!pio_claim_free_sm_and_add_program_for_gpio_range(&uart_tx_program, &pio_hw_tx, &pio_sm_tx, &offset_tx, GPIO_TX, 1, true)) {
+        panic("failed to allocate pio for tx");
+    }
+    uart_tx_program_init(pio_hw_tx, pio_sm_tx, offset_tx, GPIO_TX, SERIAL_BAUD);
+#else
+    gpio_set_function(GPIO_TX, GPIO_FUNC_UART);
+#endif
+
+// setup pio interrupt
+#if USE_PIO_FOR_RX
+    if (irq_get_exclusive_handler(pio_get_irq_num(pio_hw_rx, PIO_IRQ_TO_USE))) {
+        panic("PIO IRQ in use");
+    }
+#if USE_DMA_FOR_RX
+    irq_add_shared_handler(pio_get_irq_num(pio_hw_rx, PIO_IRQ_TO_USE), pio_irq_handler, PIO_IRQ_PRIORITY);
+    pio_set_irqn_source_enabled(pio_hw_rx, PIO_IRQ_TO_USE, pis_sm0_rx_fifo_not_empty + pio_sm_rx, true);
+    irq_set_enabled(pio_get_irq_num(pio_hw_rx, PIO_IRQ_TO_USE), true);
+#endif
+#endif
+
+// add dma handler
+#if USE_DMA_FOR_RX || USE_DMA_FOR_TX
+    if (irq_get_exclusive_handler(dma_get_irq_num(DMA_IRQ_TO_USE))) {
+        panic("DMA IRQ in use");
+    }
+    irq_add_shared_handler(dma_get_irq_num(DMA_IRQ_TO_USE), dma_irq_handler, DMA_IRQ_PRIORITY);
+    irq_set_enabled(dma_get_irq_num(DMA_IRQ_TO_USE), true);
+#endif
+
+// Setup dma for read
+#if USE_DMA_FOR_RX
+    dma_channel_rx = dma_claim_unused_channel(false);
+    if (dma_channel_rx < 0) {
+        panic("No free dma channels");
+    }
+    dma_channel_config config_rx = dma_channel_get_default_config(dma_channel_rx);
+    channel_config_set_transfer_data_size(&config_rx, DMA_SIZE_8);
+    channel_config_set_read_increment(&config_rx, false);
+    channel_config_set_write_increment(&config_rx, true);
+    read_size = sizeof(buffer_tx) - 1;
+    // enable irq for rx
+    dma_irqn_set_channel_enabled(DMA_IRQ_TO_USE, dma_channel_rx, true);
+#if USE_PIO_FOR_RX
+    // read from pio fifo
+    channel_config_set_dreq(&config_rx, pio_get_dreq(pio_hw_rx, pio_sm_rx, false));
+    // 8-bit read from the uppermost byte of the FIFO, as data is left-justified so need to add 3. Don't forget the cast!
+    dma_channel_configure(dma_channel_rx, &config_rx, buffer_rx, (io_rw_8*)&pio_hw_rx->rxf[pio_sm_rx] + 3, read_size, true); // dma started
+#else
+    // read from uart hardware
+    channel_config_set_dreq(&config_rx, uart_get_dreq(HARD_UART_INST, false));
+    dma_channel_configure(dma_channel_rx, &config_rx, buffer_rx, &uart_get_hw(HARD_UART_INST)->dr, read_size, true); // dma started
+#endif
+#endif
+
+// setup dma for write
+#if USE_DMA_FOR_TX
+    dma_channel_tx = dma_claim_unused_channel(false);
+    if (dma_channel_tx < 0) {
+        panic("No free dma channels");
+    }
+    dma_channel_config config_tx = dma_channel_get_default_config(dma_channel_tx);
+    channel_config_set_transfer_data_size(&config_tx, DMA_SIZE_8);
+    channel_config_set_read_increment(&config_tx, true);
+    channel_config_set_write_increment(&config_tx, false);
+    // enable irq for tx
+    dma_irqn_set_channel_enabled(DMA_IRQ_TO_USE, dma_channel_tx, true);
+#if USE_PIO_FOR_RX
+    // write to pio fifo
+    channel_config_set_dreq(&config_tx, pio_get_dreq(pio_hw_tx, pio_sm_tx, true));
+    dma_channel_configure(dma_channel_tx, &config_tx, &pio_hw_rx->txf[pio_sm_tx], buffer_tx, sizeof(buffer_tx) - 1, true); // dma started
+#else
+    // write to uart hardware
+    channel_config_set_dreq(&config_tx, uart_get_dreq(HARD_UART_INST, true));
+    dma_channel_configure(dma_channel_tx, &config_tx, &uart_get_hw(HARD_UART_INST)->dr, buffer_tx, sizeof(buffer_tx) - 1, true); // dma started
+#endif
+#endif
+
+// send data
+#if USE_DMA_FOR_TX
+    dma_channel_wait_for_finish_blocking(dma_channel_tx); // wait for tx
+#elif USE_PIO_FOR_TX
+    // write to the pio fifo
+    int count_pio_tx = 0;
+    while(count_pio_tx < sizeof(buffer_tx) - 1) {
+        uart_tx_program_putc(pio_hw_tx, pio_sm_tx, buffer_tx[count_pio_tx++]);
+    }
+#else
+    uart_puts(HARD_UART_INST, buffer_tx);
+#endif
+
+// Receive the data
+#if USE_DMA_FOR_RX
+    // wait for dma rx
+    dma_channel_wait_for_finish_blocking(dma_channel_rx);
+#elif USE_PIO_FOR_RX
+    // read from the pio fifo
+    int count_pio_rx = 0;
+    while(count_pio_rx < sizeof(buffer_tx) - 1) {
+        buffer_rx[count_pio_rx++] = uart_rx_program_getc(pio_hw_rx, pio_sm_rx);
+    }
+#else
+    // use the uart hardware
+    int count_uart_rx = 0;
+    while(count_uart_rx < sizeof(buffer_tx) - 1) {
+        buffer_rx[count_uart_rx++] = uart_getc(HARD_UART_INST);
+    }
+#endif
+
+    // check
+    if (memcmp(buffer_rx, buffer_tx, sizeof(buffer_tx) - 1) == 0) {
+        printf("Test passed\n");
+    } else {
+        printf("buffer_tx: >%s<\n", buffer_tx);
+        dump_bytes(buffer_tx, sizeof(buffer_tx));
+        printf("result: >%s<\n", buffer_rx);
+        dump_bytes(buffer_rx, sizeof(buffer_rx));
+        printf("Test failed\n");
+        assert(0);
+    }
+
+    // cleanup
+#if USE_DMA_FOR_TX
+    dma_irqn_set_channel_enabled(DMA_IRQ_TO_USE, dma_channel_tx, false);
+    dma_channel_unclaim(dma_channel_tx);
+#endif
+#if USE_DMA_FOR_RX
+    dma_irqn_set_channel_enabled(DMA_IRQ_TO_USE, dma_channel_rx, false);
+    dma_channel_unclaim(dma_channel_rx);
+#endif
+#if USE_DMA_FOR_RX || USE_DMA_FOR_TX
+    irq_remove_handler(dma_get_irq_num(DMA_IRQ_TO_USE), dma_irq_handler);
+    if (!irq_has_shared_handler(dma_get_irq_num(DMA_IRQ_TO_USE))) {
+        irq_set_enabled(dma_get_irq_num(DMA_IRQ_TO_USE), false);
+    }
+#endif
+#if USE_PIO_FOR_RX
+    pio_set_irqn_source_enabled(pio_hw_rx, PIO_IRQ_TO_USE, pis_sm0_rx_fifo_not_empty + pio_sm_rx, false);
+    irq_remove_handler(pio_get_irq_num(pio_hw_rx, PIO_IRQ_TO_USE), pio_irq_handler);
+    if (!irq_has_shared_handler(pio_get_irq_num(pio_hw_rx, PIO_IRQ_TO_USE))) {
+        irq_set_enabled(pio_get_irq_num(pio_hw_rx, PIO_IRQ_TO_USE), false);
+    }
+    pio_remove_program_and_unclaim_sm(&uart_rx_mini_program, pio_hw_rx, pio_sm_rx, offset_rx);
+#endif
+#if USE_PIO_FOR_TX
+    pio_remove_program_and_unclaim_sm(&uart_tx_program, pio_hw_tx, pio_sm_tx, offset_tx);
+#endif
+#if !USE_PIO_FOR_RX || !USE_PIO_FOR_TX
+    uart_deinit(HARD_UART_INST);
+#endif
+    return 0;
+}