Add pio/ir_nec (#129)

Co-authored-by: martin <admin@crossleys.biz>

pio/ir_nec/ir_loopback/ir_loopback.c

@@ -0,0 +1,67 @@
+/**
+ * Copyright (c) 2021 mjcross
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <stdio.h>
+#include "pico/stdlib.h"
+
+#include "nec_transmit.h"                           // include the library headers
+#include "nec_receive.h"
+
+// Infrared loopback example ('NEC' format)
+//
+// Need to connect an IR LED to GPIO 14 via a suitable series resistor (e.g. 1.5k)
+// and an active-low IR detector to GPIO 15 (e.g. VS1838b)
+//
+// Output is sent to stdout
+
+int main() {
+    stdio_init_all();
+
+    PIO pio = pio0;                                 // choose which PIO block to use (RP2040 has two: pio0 and pio1)
+    uint tx_gpio = 14;                              // choose which GPIO pin is connected to the IR LED
+    uint rx_gpio = 15;                              // choose which GPIO pin is connected to the IR detector
+
+    // configure and enable the state machines
+    //
+    int tx_sm = nec_tx_init (pio, tx_gpio);         // uses two state machines, 16 instructions and one IRQ
+    int rx_sm = nec_rx_init (pio, rx_gpio);         // uses one state machine and 9 instructions
+
+    if (tx_sm == -1 || rx_sm == -1) {
+        printf ("could not configure PIO\n");
+        return -1;
+    }
+
+    // transmit and receive frames
+    //
+    uint8_t tx_address = 0x00, tx_data = 0x00, rx_address, rx_data;
+    while (true) {
+
+        // create a 32-bit frame and add it to the transmit FIFO
+        //
+        uint32_t tx_frame = nec_encode_frame (tx_address, tx_data);
+        pio_sm_put (pio, tx_sm, tx_frame);
+        printf ("\nsent: %02x, %02x", tx_address, tx_data);
+
+        // allow time for the frame to be transmitted (optional)
+        //
+        sleep_ms (100);
+
+        // display any frames in the receive FIFO
+        //
+        while (!pio_sm_is_rx_fifo_empty (pio, rx_sm)) {
+            uint32_t rx_frame = pio_sm_get (pio, rx_sm);
+
+            if (nec_decode_frame (rx_frame, &rx_address, &rx_data)) {
+                printf ("\treceived: %02x, %02x", rx_address, rx_data);
+            } else {
+                printf ("\treceived: %08x", rx_frame);
+            }
+        }
+
+        sleep_ms (900);
+        tx_data += 1;
+    }
+}