Add a couple of examples of using the Max7219 LED driver chip (#209)

spi/max7219_32x8_spi/max7219_32x8_spi.c

@@ -0,0 +1,141 @@
+/**
+ * Copyright (c) 2022 Raspberry Pi (Trading) Ltd.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <stdio.h>
+#include <string.h>
+#include "pico/stdlib.h"
+#include "pico/binary_info.h"
+#include "hardware/spi.h"
+
+/* Example code to talk to a Max7219 driving an 32x8 pixel LED display via SPI
+
+   NOTE: The device is driven at 5v, but SPI communications are at 3v3
+
+   Connections on Raspberry Pi Pico board and a generic Max7219 board, other
+   boards may vary.
+
+   * GPIO 17 (pin 22) Chip select -> CS on Max7219 board
+   * GPIO 18 (pin 24) SCK/spi0_sclk -> CLK on Max7219 board
+   * GPIO 19 (pin 25) MOSI/spi0_tx -> DIN on Max7219 board
+   * 5v (pin 40) -> VCC on Max7219 board
+   * GND (pin 38)  -> GND on Max7219 board
+
+   Note: SPI devices can have a number of different naming schemes for pins. See
+   the Wikipedia page at https://en.wikipedia.org/wiki/Serial_Peripheral_Interface
+   for variations.
+
+*/
+
+// This defines how many Max7219 modules we have cascaded together, in this case, we have 4 x 8x8 matrices giving a total of 32x8
+#define NUM_MODULES 4
+
+const uint8_t CMD_NOOP = 0;
+const uint8_t CMD_DIGIT0 = 1; // Goes up to 8, for each line
+const uint8_t CMD_DECODEMODE = 9;
+const uint8_t CMD_BRIGHTNESS = 10;
+const uint8_t CMD_SCANLIMIT = 11;
+const uint8_t CMD_SHUTDOWN = 12;
+const uint8_t CMD_DISPLAYTEST = 15;
+
+#ifdef PICO_DEFAULT_SPI_CSN_PIN
+static inline void cs_select() {
+    asm volatile("nop \n nop \n nop");
+    gpio_put(PICO_DEFAULT_SPI_CSN_PIN, 0);  // Active low
+    asm volatile("nop \n nop \n nop");
+}
+
+static inline void cs_deselect() {
+    asm volatile("nop \n nop \n nop");
+    gpio_put(PICO_DEFAULT_SPI_CSN_PIN, 1);
+    asm volatile("nop \n nop \n nop");
+}
+#endif
+
+#if defined(spi_default) && defined(PICO_DEFAULT_SPI_CSN_PIN)
+static void write_register(uint8_t reg, uint8_t data) {
+    uint8_t buf[2];
+    buf[0] = reg;
+    buf[1] = data;
+    cs_select();
+    spi_write_blocking(spi_default, buf, 2);
+    cs_deselect();
+    sleep_ms(1);
+}
+
+static void write_register_all(uint8_t reg, uint8_t data) {
+    uint8_t buf[2];
+    buf[0] = reg;
+    buf[1] = data;
+    cs_select();
+    for (int i = 0; i< NUM_MODULES;i++) {
+        spi_write_blocking(spi_default, buf, 2);
+    }
+    cs_deselect();
+}
+
+#endif
+
+int main() {
+    stdio_init_all();
+
+#if !defined(spi_default) || !defined(PICO_DEFAULT_SPI_SCK_PIN) || !defined(PICO_DEFAULT_SPI_TX_PIN) || !defined(PICO_DEFAULT_SPI_CSN_PIN)
+#warning spi/max7219_32x8_spi example requires a board with SPI pins
+    puts("Default SPI pins were not defined");
+#else
+
+    printf("Hello, max7219! Drawing things on a LED matrix since 2022...\n");
+
+    // This example will use SPI0 at 10MHz.
+    spi_init(spi_default, 10 * 1000 * 1000);
+    gpio_set_function(PICO_DEFAULT_SPI_SCK_PIN, GPIO_FUNC_SPI);
+    gpio_set_function(PICO_DEFAULT_SPI_TX_PIN, GPIO_FUNC_SPI);
+
+    // Make the SPI pins available to picotool
+    bi_decl(bi_2pins_with_func(PICO_DEFAULT_SPI_TX_PIN, PICO_DEFAULT_SPI_SCK_PIN, GPIO_FUNC_SPI));
+
+    // Chip select is active-low, so we'll initialise it to a driven-high state
+    gpio_init(PICO_DEFAULT_SPI_CSN_PIN);
+    gpio_set_dir(PICO_DEFAULT_SPI_CSN_PIN, GPIO_OUT);
+    gpio_put(PICO_DEFAULT_SPI_CSN_PIN, 1);
+
+    // Make the CS pin available to picotool
+    bi_decl(bi_1pin_with_name(PICO_DEFAULT_SPI_CSN_PIN, "SPI CS"));
+
+    // Send init sequence to device
+
+    write_register_all(CMD_SHUTDOWN, 0);
+    write_register_all(CMD_DISPLAYTEST, 0);
+    write_register_all(CMD_SCANLIMIT, 7);  // Use all lines
+    write_register_all(CMD_DECODEMODE, 0); // No BCD decode, just use bit pattern.
+    write_register_all(CMD_SHUTDOWN, 1);
+    write_register_all(CMD_BRIGHTNESS, 8);
+
+    for (int i=0; i<256; i++) {
+        for (int j=0; j<8; j++) {
+            write_register_all(CMD_DIGIT0+j, i);
+        }
+        sleep_ms(20);
+    }
+
+    int bright = 1;
+    while (true) {
+        for (int i=0; i<8; i++) {
+            if (bright & 1) {
+                write_register_all(CMD_DIGIT0 + i, 170 >> (i%2));
+            } else {
+                write_register_all(CMD_DIGIT0 + i, (170 >> 1) << (i%2));
+            }       
+
+            write_register_all(CMD_BRIGHTNESS, bright % 16);
+        }
+        sleep_ms(250);
+
+        bright++;
+    }
+
+    return 0;
+#endif
+}