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Diffstat (limited to 'tests/test-usart-dma.cpp')
| -rw-r--r-- | tests/test-usart-dma.cpp | 211 |
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; +} |