Datasheet


NOTE
Having two system interrupt lines allows different channel completion interrupts to be routed to different cores, or to
preempt one another on the same core if one channel is more time-critical.
When the interrupt is asserted, the processor can be configured to drop whatever it is doing and call a user-specified
handler function. The handler can reconfigure and restart the channel. When the handler exits, the processor returns to
the interrupted code running in the foreground.
Pico Examples: https://github.com/raspberrypi/pico-examples/tree/master/dma/channel_irq/channel_irq.c Lines 35 - 52
35 void dma_handler() {
36 static int pwm_level = 0;
37 static uint32_t wavetable[N_PWM_LEVELS];
38 static bool first_run = true;
39 // Entry number `i` has `i` one bits and `(32 - i)` zero bits.
40 if (first_run) {
41 first_run = false;
42 for (int i = 0; i < N_PWM_LEVELS; ++i)
43 wavetable[i] = ~(~0u << i);
44 }
45
46 // Clear the interrupt request.
47 dma_hw->ints0 = 1u << dma_chan;
48 // Give the channel a new wave table entry to read from, and re-trigger it
49 dma_channel_set_read_addr(dma_chan, &wavetable[pwm_level], true);
50
51 pwm_level = (pwm_level + 1) % N_PWM_LEVELS;
52 }
In many cases, most of the configuration can be done the first time the channel is started, and only addresses and
transfer lengths need reprogramming in the DMA handler.
Pico Examples: https://github.com/raspberrypi/pico-examples/tree/master/dma/channel_irq/channel_irq.c Lines 54 - 94
54 int main() {
55 #ifndef PICO_DEFAULT_LED_PIN
56 #warning dma/channel_irq example requires a board with a regular LED
57 #else
58 // Set up a PIO state machine to serialise our bits
59 uint offset = pio_add_program(pio0, &pio_serialiser_program);
60 pio_serialiser_program_init(pio0, 0, offset, PICO_DEFAULT_LED_PIN, PIO_SERIAL_CLKDIV);
61
62 // Configure a channel to write the same word (32 bits) repeatedly to PIO0
63 // SM0's TX FIFO, paced by the data request signal from that peripheral.
64 dma_chan = dma_claim_unused_channel(true);
65 dma_channel_config c = dma_channel_get_default_config(dma_chan);
66 channel_config_set_transfer_data_size(&c, DMA_SIZE_32);
67 channel_config_set_read_increment(&c, false);
68 channel_config_set_dreq(&c, DREQ_PIO0_TX0);
69
70 dma_channel_configure(
71 dma_chan,
72 &c,
73 &pio0_hw->txf[0], // Write address (only need to set this once)
74 NULL, // Don't provide a read address yet
75 PWM_REPEAT_COUNT, // Write the same value many times, then halt and interrupt
76 false // Don't start yet
77 );
78
RP2040 Datasheet
2.5. DMA 99