kopia lustrzana https://github.com/pimoroni/pimoroni-pico
Pure C++ HUB75 example
This code is intentionally written in C++ to illustrate the basics of driving HUB75 without being overly complicated to read and understand. Tested on a 32x32 panel and a 64x64 "FM6126A" panel, for which this code includes a magic pair of register settings.pull/193/head
Phil Howard
rodzic
e249113fea
commit
babe8a7760
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@ -37,3 +37,4 @@ add_subdirectory(pico_audio)
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add_subdirectory(pico_wireless)
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add_subdirectory(plasma2040)
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add_subdirectory(interstate75)
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@ -0,0 +1 @@
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include(interstate75_hello_world.cmake)
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@ -0,0 +1,16 @@
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set(OUTPUT_NAME interstate75_hello_world)
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add_executable(${OUTPUT_NAME} interstate75_hello_world.cpp)
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# enable usb output
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pico_enable_stdio_usb(${OUTPUT_NAME} 1)
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pico_add_extra_outputs(${OUTPUT_NAME})
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target_link_libraries(${OUTPUT_NAME}
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pico_stdlib
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pico_multicore
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hardware_pio
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hardware_dma
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)
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pico_generate_pio_header(${OUTPUT_NAME} ${CMAKE_CURRENT_LIST_DIR}/hub75.pio)
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@ -0,0 +1,307 @@
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#include <stdio.h>
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#include <math.h>
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#include <cstdint>
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#include <cstring>
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#include "pico/stdlib.h"
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#include "pico/multicore.h"
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#include "hardware/vreg.h"
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#include "common/pimoroni_common.hpp"
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using namespace pimoroni;
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/* Interstate 75 - HUB75 from basic principles.
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While trying to get our I75 running I soon realised that I couldn't find any documentation or basics on the HUB75 protocol.
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Yes there were libraries and tidbits that were seemingly loosely related, but nothing really laying out clear steps to update the 32x32 display on my desk.
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So I wrote this.
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This code may not be technically correct, but the results are visually appealing and fast enough.
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More importantly, the code is legible and doesn't hide any implementation details beneath the inscrutable veneer of PIO.
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No interpolators, no DMA, no PIO here- if you want a beautifully optimised library for HUB75 output then this... isn't it.
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Just pure C. Pure CPU. Running on RP2040s Core1.
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*/
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// Display size in pixels
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// Should be either 64x64 or 32x32 but perhaps 64x32 an other sizes will work.
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// Note: this example uses only 5 address lines so it's limited to 32*2 pixels.
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const uint8_t WIDTH = 64;
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const uint8_t HEIGHT = 64;
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// Settings below are correct for I76, change them to suit your setup:
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// Top half of display - 16 rows on a 32x32 panel
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const uint PIN_R0 = 0;
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const uint PIN_G0 = 1;
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const uint PIN_B0 = 2;
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// Bottom half of display - 16 rows on a 64x64 panel
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const uint PIN_R1 = 3;
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const uint PIN_G1 = 4;
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const uint PIN_B1 = 5;
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// Address pins, 5 lines = 2^5 = 32 values (max 64x64 display)
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const uint PIN_ROW_A = 6;
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const uint PIN_ROW_B = 7;
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const uint PIN_ROW_C = 8;
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const uint PIN_ROW_D = 9;
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const uint PIN_ROW_E = 10;
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// Sundry things
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const uint PIN_CLK = 11; // Clock
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const uint PIN_STB = 12; // Strobe/Latch
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const uint PIN_OE = 13; // Output Enable
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const bool CLK_POLARITY = 1;
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const bool STB_POLARITY = 1;
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const bool OE_POLARITY = 0;
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// User buttons and status LED
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const uint PIN_SW_A = 14;
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const uint PIN_SW_USER = 23;
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const uint PIN_LED_R = 16;
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const uint PIN_LED_G = 17;
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const uint PIN_LED_B = 18;
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// This gamma table is used to correct our 8-bit (0-255) colours up to 11-bit,
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// allowing us to gamma correct without losing dynamic range.
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const uint16_t GAMMA[256] = {
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0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15,
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16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31,
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32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 47, 50,
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52, 54, 57, 59, 62, 65, 67, 70, 73, 76, 79, 82, 85, 88, 91, 94,
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98, 101, 105, 108, 112, 115, 119, 123, 127, 131, 135, 139, 143, 147, 151, 155,
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160, 164, 169, 173, 178, 183, 187, 192, 197, 202, 207, 212, 217, 223, 228, 233,
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239, 244, 250, 255, 261, 267, 273, 279, 285, 291, 297, 303, 309, 316, 322, 328,
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335, 342, 348, 355, 362, 369, 376, 383, 390, 397, 404, 412, 419, 427, 434, 442,
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449, 457, 465, 473, 481, 489, 497, 505, 513, 522, 530, 539, 547, 556, 565, 573,
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582, 591, 600, 609, 618, 628, 637, 646, 656, 665, 675, 685, 694, 704, 714, 724,
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734, 744, 755, 765, 775, 786, 796, 807, 817, 828, 839, 850, 861, 872, 883, 894,
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905, 917, 928, 940, 951, 963, 975, 987, 998, 1010, 1022, 1035, 1047, 1059, 1071, 1084,
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1096, 1109, 1122, 1135, 1147, 1160, 1173, 1186, 1199, 1213, 1226, 1239, 1253, 1266, 1280, 1294,
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1308, 1321, 1335, 1349, 1364, 1378, 1392, 1406, 1421, 1435, 1450, 1465, 1479, 1494, 1509, 1524,
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1539, 1554, 1570, 1585, 1600, 1616, 1631, 1647, 1663, 1678, 1694, 1710, 1726, 1743, 1759, 1775,
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1791, 1808, 1824, 1841, 1858, 1875, 1891, 1908, 1925, 1943, 1960, 1977, 1994, 2012, 2029, 2047};
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// We don't *need* to make Pixel a fancy struct with RGB values, but it helps.
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#pragma pack(push, 1)
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struct alignas(4) Pixel {
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uint8_t r;
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uint8_t g;
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uint8_t b;
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uint8_t _;
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constexpr Pixel() : r(0), g(0), b(0), _(0) {};
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constexpr Pixel(uint8_t r, uint8_t g, uint8_t b) : r(r), g(g), b(b), _(0) {};
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constexpr Pixel(uint r, uint g, uint b) : r(r), g(g), b(b), _(0) {};
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constexpr Pixel(float r, float g, float b) : r((uint8_t)(r * 255.0f)), g((uint8_t)(g * 255.0f)), b((uint8_t)(b * 255.0f)), _(0) {};
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};
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#pragma pack(pop)
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// Create our front and back buffers.
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// We'll draw into the frontbuffer and then copy everything into the backbuffer which will be used to refresh the screen.
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// Double-buffering the display avoids screen tearing with fast animations or slow update rates.
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Pixel backbuffer[WIDTH][HEIGHT];
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Pixel frontbuffer[WIDTH][HEIGHT];
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// Basic function to convert Hue, Saturation and Value to an RGB colour
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Pixel hsv_to_rgb(float h, float s, float v) {
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if(h < 0.0f) {
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h = 1.0f + fmod(h, 1.0f);
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}
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int i = int(h * 6);
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float f = h * 6 - i;
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v = v * 255.0f;
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float sv = s * v;
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float fsv = f * sv;
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auto p = uint8_t(-sv + v);
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auto q = uint8_t(-fsv + v);
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auto t = uint8_t(fsv - sv + v);
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uint8_t bv = uint8_t(v);
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switch (i % 6) {
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default:
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case 0: return Pixel(bv, t, p);
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case 1: return Pixel(q, bv, p);
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case 2: return Pixel(p, bv, t);
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case 3: return Pixel(p, q, bv);
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case 4: return Pixel(t, p, bv);
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case 5: return Pixel(bv, p, q);
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}
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}
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// Required for FM6126A-based displays which need some register config/init to work properly
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void FM6126A_write_register(uint16_t value, uint8_t position) {
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uint8_t threshold = WIDTH - position;
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for(auto i = 0u; i < WIDTH; i++) {
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auto j = i % 16;
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bool b = value & (1 << j);
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gpio_put(PIN_R0, b);
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gpio_put(PIN_G0, b);
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gpio_put(PIN_B0, b);
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gpio_put(PIN_R1, b);
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gpio_put(PIN_G1, b);
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gpio_put(PIN_B1, b);
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// Assert strobe/latch if i > threshold
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// This somehow indicates to the FM6126A which register we want to write :|
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gpio_put(PIN_STB, i > threshold);
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gpio_put(PIN_CLK, CLK_POLARITY);
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sleep_us(10);
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gpio_put(PIN_CLK, !CLK_POLARITY);
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}
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}
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void hub75_display_update() {
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// Ridiculous register write nonsense for the FM6126A-based 64x64 matrix
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FM6126A_write_register(0b1111111111111110, 12);
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FM6126A_write_register(0b0000001000000000, 13);
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while (true) {
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// 0. Copy the contents of the front buffer into our backbuffer for output to the display.
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// This uses another whole backbuffer worth of memory, but prevents visual tearing at low frequencies.
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memcpy((uint8_t *)backbuffer, (uint8_t *)frontbuffer, WIDTH * HEIGHT * sizeof(Pixel));
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// Step through 0b00000001, 0b00000010, 0b00000100 etc
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for(auto bit = 1u; bit < 1 << 11; bit <<= 1) {
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// Since the display is in split into two equal halves, we step through y from 0 to HEIGHT / 2
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for(auto y = 0u; y < HEIGHT / 2; y++) {
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// 1. Shift out pixel data
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// Shift out WIDTH pixels to the top and bottom half of the display
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for(auto x = 0u; x < WIDTH; x++) {
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// Get the current pixel for top/bottom half
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// This is easy since we just need the pixels at X/Y and X/Y+HEIGHT/2
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Pixel pixel_top = backbuffer[x][y];
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Pixel pixel_bottom = backbuffer[x][y + HEIGHT / 2];
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// Gamma correct the colour values from 8-bit to 11-bit
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uint16_t pixel_top_b = GAMMA[pixel_top.b];
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uint16_t pixel_top_g = GAMMA[pixel_top.g];
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uint16_t pixel_top_r = GAMMA[pixel_top.r];
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uint16_t pixel_bottom_b = GAMMA[pixel_bottom.b];
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uint16_t pixel_bottom_g = GAMMA[pixel_bottom.g];
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uint16_t pixel_bottom_r = GAMMA[pixel_bottom.r];
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// Set the clock low while we set up the data pins
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gpio_put(PIN_CLK, !CLK_POLARITY);
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// Top half
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gpio_put(PIN_R0, (bool)(pixel_top_r & bit));
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gpio_put(PIN_G0, (bool)(pixel_top_g & bit));
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gpio_put(PIN_B0, (bool)(pixel_top_b & bit));
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// Bottom half
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gpio_put(PIN_R1, (bool)(pixel_bottom_r & bit));
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gpio_put(PIN_G1, (bool)(pixel_bottom_g & bit));
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gpio_put(PIN_B1, (bool)(pixel_bottom_b & bit));
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// Wiggle the clock
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// The gamma correction above will ensure our clock stays asserted
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// for some small amount of time, avoiding the need for an explicit delay.
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gpio_put(PIN_CLK, CLK_POLARITY);
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}
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// 2. Set address pins
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// Set the address pins to reflect the row to light up: 0 through 15 for 32x32 pixel panels
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// We decode our 5-bit row address out onto the 5 GPIO pins by masking each bit in turn.
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gpio_put_masked(0b11111 << PIN_ROW_A, y << PIN_ROW_A);
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// 3. Assert latch/strobe signal (STB)
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// This latches all the values we've just clocked into the column shift registers.
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// The values will appear on the output pins, ready for the display to be driven.
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gpio_put(PIN_STB, STB_POLARITY);
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// 4. Asset the output-enable signal (OE)
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// This turns on the display for a brief period to light the selected rows/columns.
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gpio_put(PIN_OE, OE_POLARITY);
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// 4. Delay
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// Delay for a period of time coressponding to "bit"'s significance
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for(auto s = 0u; s < bit; ++s) {
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// The basic premise here is that "bit" will step through the values:
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// 1, 2, 4, 8, 16, 32, 64, etc in sequence.
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// If we plug this number into a delay loop, we'll get different magnitudes
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// of delay which correspond exactly to the significance of each bit.
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// The longer we delay here, the slower the overall panel refresh rate will be.
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// But we need to delay *just enough* that we're not under-driving the panel and
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// losing out on brightness.
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asm volatile("nop \nnop"); // Batman!
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}
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// 5. De-assert latch/strobe signal (STB) + output-enable signal (OE)
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// Ready to go again!
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gpio_put(PIN_STB, !STB_POLARITY);
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gpio_put(PIN_OE, !OE_POLARITY);
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// 6. GOTO 1.
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}
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sleep_us(1);
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}
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}
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}
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int main() {
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// 1.3v allows overclock to ~280000-300000 but YMMV. Faster clock = faster screen update rate!
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// vreg_set_voltage(VREG_VOLTAGE_1_30);
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// sleep_ms(100);
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// 200MHz is roughly about the lower limit for driving a 64x64 display smoothly.
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// Just don't look at it out of the corner of your eye.
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set_sys_clock_khz(200000, false);
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// Set up allllll the GPIO
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gpio_init(PIN_R0); gpio_set_function(PIN_R0, GPIO_FUNC_SIO); gpio_set_dir(PIN_R0, true);
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gpio_init(PIN_G0); gpio_set_function(PIN_G0, GPIO_FUNC_SIO); gpio_set_dir(PIN_G0, true);
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gpio_init(PIN_B0); gpio_set_function(PIN_B0, GPIO_FUNC_SIO); gpio_set_dir(PIN_B0, true);
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gpio_init(PIN_R1); gpio_set_function(PIN_R1, GPIO_FUNC_SIO); gpio_set_dir(PIN_R1, true);
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gpio_init(PIN_G1); gpio_set_function(PIN_G1, GPIO_FUNC_SIO); gpio_set_dir(PIN_G1, true);
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gpio_init(PIN_B1); gpio_set_function(PIN_B1, GPIO_FUNC_SIO); gpio_set_dir(PIN_B1, true);
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gpio_init(PIN_ROW_A); gpio_set_function(PIN_ROW_A, GPIO_FUNC_SIO); gpio_set_dir(PIN_ROW_A, true);
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gpio_init(PIN_ROW_B); gpio_set_function(PIN_ROW_B, GPIO_FUNC_SIO); gpio_set_dir(PIN_ROW_B, true);
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gpio_init(PIN_ROW_C); gpio_set_function(PIN_ROW_C, GPIO_FUNC_SIO); gpio_set_dir(PIN_ROW_C, true);
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gpio_init(PIN_ROW_D); gpio_set_function(PIN_ROW_D, GPIO_FUNC_SIO); gpio_set_dir(PIN_ROW_D, true);
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gpio_init(PIN_ROW_E); gpio_set_function(PIN_ROW_E, GPIO_FUNC_SIO); gpio_set_dir(PIN_ROW_E, true);
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gpio_init(PIN_CLK); gpio_set_function(PIN_CLK, GPIO_FUNC_SIO); gpio_set_dir(PIN_CLK, true);
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gpio_init(PIN_STB); gpio_set_function(PIN_STB, GPIO_FUNC_SIO); gpio_set_dir(PIN_STB, true);
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gpio_init(PIN_OE); gpio_set_function(PIN_OE, GPIO_FUNC_SIO); gpio_set_dir(PIN_OE, true);
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// Launch the display update routine on Core 1, it's hungry for cycles!
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multicore_launch_core1(hub75_display_update);
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// Basic loop to draw something to the screen.
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// This gets the distance from the middle of the display and uses it to paint a circular colour cycle.
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while (true) {
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float offset = millis() / 10000.0f;
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for(auto x = 0u; x < WIDTH; x++) {
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for(auto y = 0u; y < HEIGHT; y++) {
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// Center our rainbow circles
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float x1 = ((int)x - WIDTH / 2);
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float y1 = ((int)y - HEIGHT / 2);
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// Get hue as the distance from the display center as float from 0.0 to 1.0f.
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float h = float(x1*x1 + y1*y1) / float(WIDTH*WIDTH + HEIGHT*HEIGHT);
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// Offset our hue to animate the effect
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h -= offset;
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frontbuffer[x][y] = hsv_to_rgb(h, 1.0f, 1.0f);
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}
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}
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}
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}
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