refactor: move test-style examples to ./tests

1 files changed, 211 insertions, 0 deletions

diff --git a/tests/test-usart-dma.cpp b/tests/test-usart-dma.cpp
new file mode 100644
index 0000000..7d6d8b9
--- /dev/null
+++ b/tests/test-usart-dma.cpp
@@ -0,0 +1,211 @@
+/**
+ * @file tests/test-usart-dma.cpp
+ * @author Marti Bolivar <mbolivar@leaflabs.com>
+ *
+ * Simple test of DMA used with a USART receiver.
+ *
+ * Configures a USART receiver for use with DMA.  Received bytes are
+ * placed into a buffer, with an interrupt firing when the buffer is
+ * full.  At that point, the USART transmitter will print the contents
+ * of the byte buffer.  The buffer is continually filled and refilled
+ * in this manner.
+ *
+ * This example isn't very robust; don't use it in production.  In
+ * particular, since the buffer keeps filling (DMA_CIRC_MODE is set),
+ * if you keep sending characters after filling the buffer, you'll
+ * overwrite earlier bytes; this may happen before those earlier bytes
+ * are done printing. (Typing quickly and seeing how it affects the
+ * output is a fun way to make sense of how the interrupts and the
+ * main thread of execution interleave.)
+ *
+ * This code is released into the public domain.
+ */
+
+#include <libmaple/dma.h>
+#include <libmaple/usart.h>
+#include <libmaple/gpio.h>
+
+#include <wirish/wirish.h>
+
+/*
+ * Configuration and state
+ */
+
+// Serial port and DMA configuration. You can change these to suit
+// your purposes.
+HardwareSerial *serial = &Serial2;
+#define USART_DMA_DEV DMA1
+#if STM32_MCU_SERIES == STM32_SERIES_F1
+// On STM32F1 microcontrollers (like what's on Maple and Maple Mini),
+// dma tubes are channels.
+#define USART_RX_DMA_TUBE DMA_CH6
+#elif (STM32_MCU_SERIES == STM32_SERIES_F2 || \
+       STM32_MCU_SERIES == STM32_SERIES_F4)
+// On STM32F2 and STM32F4 microcontrollers (Maple 2 will have an F4),
+// dma tubes are streams.
+#define USART_RX_DMA_TUBE DMA_S5
+#else
+#error "unsupported stm32 series"
+#endif
+// The serial port will make a DMA request each time it receives data.
+// This is the dma_request_src we use to tell the DMA tube to handle
+// that DMA request.
+#define USART_DMA_REQ_SRC DMA_REQ_SRC_USART2_RX
+#define BAUD 9600
+
+// This will store the DMA configuration for USART RX.
+dma_tube_config tube_config;
+
+// This will store received USART characters.
+#define BUF_SIZE 20
+char rx_buf[BUF_SIZE];
+
+// The interrupt handler, rx_dma_irq(), sets this to 1.
+volatile uint32 irq_fired = 0;
+// Used to store DMA interrupt status register (ISR) bits inside
+// rx_dma_irq(). This helps explain what's going on inside loop(); see
+// comments below.
+volatile uint32 isr = 0;
+
+/*
+ * Helper functions
+ */
+
+// This is our DMA interrupt handler.
+void rx_dma_irq(void) {
+    irq_fired = 1;
+    isr = dma_get_isr_bits(USART_DMA_DEV, USART_RX_DMA_TUBE);
+}
+
+// Configure the USART receiver for use with DMA:
+// 1. Turn it on.
+// 2. Set the "DMA request on RX" bit in USART_CR3 (USART_CR3_DMAR).
+void setup_usart(void) {
+    serial->begin(BAUD);
+    usart_dev *serial_dev = serial->c_dev();
+    serial_dev->regs->CR3 = USART_CR3_DMAR;
+}
+
+// Set up our dma_tube_config structure. (We could have done this
+// above, when we declared tube_config, but having this function makes
+// it easier to explain what's going on).
+void setup_tube_config(void) {
+    // We're receiving from the USART data register. serial->c_dev()
+    // returns a pointer to the libmaple usart_dev for that serial
+    // port, so this is a pointer to its data register.
+    tube_config.tube_src = &serial->c_dev()->regs->DR;
+    // We're only interested in the bottom 8 bits of that data register.
+    tube_config.tube_src_size = DMA_SIZE_8BITS;
+    // We're storing to rx_buf.
+    tube_config.tube_dst = rx_buf;
+    // rx_buf is a char array, and a "char" takes up 8 bits on STM32.
+    tube_config.tube_dst_size = DMA_SIZE_8BITS;
+    // Only fill BUF_SIZE - 1 characters, to leave a null byte at the end.
+    tube_config.tube_nr_xfers = BUF_SIZE - 1;
+    // Flags:
+    // - DMA_CFG_DST_INC so we start at the beginning of rx_buf and
+    //   fill towards the end.
+    // - DMA_CFG_CIRC so we go back to the beginning and start over when
+    //   rx_buf fills up.
+    // - DMA_CFG_CMPLT_IE to turn on interrupts on transfer completion.
+    tube_config.tube_flags = DMA_CFG_DST_INC | DMA_CFG_CIRC | DMA_CFG_CMPLT_IE;
+    // Target data: none. It's important to set this to NULL if you
+    // don't have any special (microcontroller-specific) configuration
+    // in mind, which we don't.
+    tube_config.target_data = NULL;
+    // DMA request source.
+    tube_config.tube_req_src = USART_DMA_REQ_SRC;
+}
+
+// Configure the DMA controller to serve DMA requests from the USART.
+void setup_dma_xfer(void) {
+    // First, turn it on.
+    dma_init(USART_DMA_DEV);
+    // Next, configure it by calling dma_tube_cfg(), and check to make
+    // sure it succeeded. DMA tubes have many restrictions on their
+    // configuration, and there are configurations which work on some
+    // types of STM32 but not others. libmaple tries hard to make
+    // things just work, but checking the return status is important!
+    int status = dma_tube_cfg(USART_DMA_DEV, USART_RX_DMA_TUBE, &tube_config);
+    ASSERT(status == DMA_TUBE_CFG_SUCCESS);
+    // Now we'll perform any other configuration we want. For this
+    // example, we attach an interrupt handler.
+    dma_attach_interrupt(USART_DMA_DEV, USART_RX_DMA_TUBE, rx_dma_irq);
+    // Turn on the DMA tube. It will now begin serving requests.
+    dma_enable(USART_DMA_DEV, USART_RX_DMA_TUBE);
+}
+
+/*
+ * setup() and loop()
+ */
+
+void setup(void) {
+    pinMode(BOARD_LED_PIN, OUTPUT);
+    setup_tube_config();
+    setup_dma_xfer();
+    setup_usart();
+}
+
+void loop(void) {
+    toggleLED();
+    delay(100);
+
+    // See if the interrupt handler got called since the last time we
+    // checked.
+    if (irq_fired) {
+        serial->println("** IRQ **");
+        // Notice how the interrupt status register (ISR) bits show
+        // transfer complete _and_ half-complete here, but the ISR
+        // bits we print next will be zero. That's because the
+        // variable "isr" gets set _inside_ rx_dma_irq(). After it
+        // exits, libmaple cleans up by clearing the tube's ISR
+        // bits. (If it didn't, and we forgot to, the interrupt would
+        // repeatedly fire forever.)
+        serial->print("ISR bits: 0x");
+        serial->println(isr, HEX);
+        irq_fired = 0;
+    }
+
+    // Print the ISR bits.
+    //
+    // Notice that the "transfer half-complete" ISR flag gets set when
+    // we reach the rx_buf half-way point. This is true even though we
+    // don't tell the DMA controller to interrupt us on a
+    // half-complete transfer. That is, the ISR bits get set at the
+    // right times no matter what; we just don't get interrupted
+    // unless we asked. (If an error or other problem occurs, the
+    // relevant ISR bits will get set in the same way).
+    serial->print("[");
+    serial->print(millis());
+    serial->print("]\tISR bits: 0x");
+    uint8 isr_bits = dma_get_isr_bits(USART_DMA_DEV, USART_RX_DMA_TUBE);
+    serial->print(isr_bits, HEX);
+
+    // Print the contents of rx_buf. If you keep typing after it fills
+    // up, the new characters will overwrite the old ones, thanks to
+    // DMA_CIRC_MODE.
+    serial->print("\tCharacter buffer contents: '");
+    serial->print(rx_buf);
+    serial->println("'");
+    if (isr_bits == 0x7) {
+        serial->println("** Clearing ISR bits.");
+        dma_clear_isr_bits(USART_DMA_DEV, USART_RX_DMA_TUBE);
+    }
+}
+
+// ------- init() and main() --------------------------------------------------
+
+// Force init to be called *first*, i.e. before static object allocation.
+// Otherwise, statically allocated objects that need libmaple may fail.
+__attribute__((constructor)) void premain() {
+    init();
+}
+
+int main(void) {
+    setup();
+
+    while (true) {
+        loop();
+    }
+    return 0;
+}