diff options
| -rw-r--r-- | examples/test-usart-dma.cpp | 127 |
1 files changed, 78 insertions, 49 deletions
diff --git a/examples/test-usart-dma.cpp b/examples/test-usart-dma.cpp index 10ebe8b..7dafc3a 100644 --- a/examples/test-usart-dma.cpp +++ b/examples/test-usart-dma.cpp @@ -12,9 +12,9 @@ * * 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 typing after filling the buffer, you'll overwrite - * earlier bytes; this may happen before those earlier bytes are done - * printing. + * if you keep sending characters after filling the buffer, you'll + * overwrite earlier bytes; this may happen before those earlier bytes + * are done printing. * * This code is released into the public domain. */ @@ -25,29 +25,65 @@ #include <wirish/wirish.h> -#define BAUD 9600 +/* + * Configuration and state + */ +// USART and DMA configuration #define USART USART2 #define USART_HWSER Serial2 #define USART_DMA_DEV DMA1 #define USART_RX_DMA_CHANNEL DMA_CH6 -#define USART_TX BOARD_USART2_TX_PIN -#define USART_RX BOARD_USART2_RX_PIN - -#define BUF_SIZE 8 -uint8 rx_buf[BUF_SIZE]; +#define BAUD 9600 -dma_irq_cause irq_cause; +// 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 the 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_CHANNEL); +} + +// 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 init_usart(void) { + USART_HWSER.begin(BAUD); + USART->regs->CR3 = USART_CR3_DMAR; +} + +// Configure the DMA controller to serve DMA requests from the USART. +void init_dma_xfer(void) { + dma_init(USART_DMA_DEV); + dma_setup_transfer(USART_DMA_DEV, USART_RX_DMA_CHANNEL, + &USART->regs->DR, DMA_SIZE_8BITS, + rx_buf, DMA_SIZE_8BITS, + (DMA_MINC_MODE | DMA_CIRC_MODE | DMA_TRNS_CMPLT)); + dma_set_num_transfers(USART_DMA_DEV, USART_RX_DMA_CHANNEL, + BUF_SIZE - 1); + dma_attach_interrupt(USART_DMA_DEV, USART_RX_DMA_CHANNEL, rx_dma_irq); + dma_enable(USART_DMA_DEV, USART_RX_DMA_CHANNEL); +} -void init_usart(void); -void init_dma_xfer(void); -void rx_dma_irq(void); +/* + * setup() and loop() + */ void setup(void) { pinMode(BOARD_LED_PIN, OUTPUT); - + rx_buf[BUF_SIZE - 1] = '\0'; // null-terminate rx_buf so we can print it init_dma_xfer(); init_usart(); } @@ -56,56 +92,49 @@ void loop(void) { toggleLED(); delay(100); - dma_channel_reg_map *ch_regs = dma_channel_regs(USART_DMA_DEV, - USART_RX_DMA_CHANNEL); + // See if the interrupt handler got called since the last time we + // checked. if (irq_fired) { USART_HWSER.println("** IRQ **"); + // Notice how the 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 ISR bits. (If it didn't, and we forgot to, the + // interrupt would repeatedly fire forever.) + USART_HWSER.print("ISR bits: 0x"); + USART_HWSER.println(isr, HEX); irq_fired = 0; } + + // Print the ISR (interrupt status register) 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). USART_HWSER.print("["); USART_HWSER.print(millis()); USART_HWSER.print("]\tISR bits: 0x"); uint8 isr_bits = dma_get_isr_bits(USART_DMA_DEV, USART_RX_DMA_CHANNEL); USART_HWSER.print(isr_bits, HEX); - USART_HWSER.print("\tCCR: 0x"); - USART_HWSER.print(ch_regs->CCR, HEX); - USART_HWSER.print("\tCNDTR: 0x"); - USART_HWSER.print(ch_regs->CNDTR, HEX); - USART_HWSER.print("\tBuffer contents: "); - for (int i = 0; i < BUF_SIZE; i++) { - USART_HWSER.print('\''); - USART_HWSER.print(rx_buf[i]); - USART_HWSER.print('\''); - if (i < BUF_SIZE - 1) USART_HWSER.print(", "); - } - USART_HWSER.println(); + + // 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. + USART_HWSER.print("\tCharacter buffer contents: '"); + USART_HWSER.print(rx_buf); + USART_HWSER.println("'"); if (isr_bits == 0x7) { USART_HWSER.println("** Clearing ISR bits."); dma_clear_isr_bits(USART_DMA_DEV, USART_RX_DMA_CHANNEL); } } -/* Configure USART receiver for use with DMA */ -void init_usart(void) { - USART_HWSER.begin(BAUD); - USART->regs->CR3 = USART_CR3_DMAR; -} - -/* Configure DMA transmission */ -void init_dma_xfer(void) { - dma_init(USART_DMA_DEV); - dma_setup_transfer(USART_DMA_DEV, USART_RX_DMA_CHANNEL, - &USART->regs->DR, DMA_SIZE_8BITS, - rx_buf, DMA_SIZE_8BITS, - (DMA_MINC_MODE | DMA_CIRC_MODE | DMA_TRNS_CMPLT)); - dma_set_num_transfers(USART_DMA_DEV, USART_RX_DMA_CHANNEL, BUF_SIZE); - dma_attach_interrupt(USART_DMA_DEV, USART_RX_DMA_CHANNEL, rx_dma_irq); - dma_enable(USART_DMA_DEV, USART_RX_DMA_CHANNEL); -} - -void rx_dma_irq(void) { - irq_fired = true; -} +// ------- init() and main() -------------------------------------------------- // Force init to be called *first*, i.e. before static object allocation. // Otherwise, statically allocated objects that need libmaple may fail. |