Added constants

0x0017_constants/.gitignore

@@ -1,5 +1,2 @@
-.idea
-_deps
-cmake-*
 build
-.DS_Store
+!.vscode/*

0x0017_constants/.vscode/.cortex-debug.peripherals.state.json

@@ -1 +0,0 @@
-[]

0x0017_constants/.vscode/.cortex-debug.registers.state.json

@@ -1 +0,0 @@
-[]

0x0017_constants/.vscode/c_cpp_properties.json

@@ -1,18 +1,22 @@
 {
-  "configurations": [
+    "configurations": [
-    {
+        {
-      "name": "Pico",
+            "name": "Pico",
-      "includePath": [
+            "includePath": [
-        "${workspaceFolder}/**",
+                "${workspaceFolder}/**",
-        "${env:PICO_SDK_PATH}/**"
+                "${userHome}/.pico-sdk/sdk/2.2.0/**"
-      ],
+            ],
-      "defines": [],
+            "forcedInclude": [
-      "compilerPath": "${env:PICO_INSTALL_PATH}/gcc-arm-none-eabi/bin/arm-none-eabi-gcc.exe",
+                "${workspaceFolder}/build/generated/pico_base/pico/config_autogen.h",
-      "cStandard": "c11",
+                "${userHome}/.pico-sdk/sdk/2.2.0/src/common/pico_base_headers/include/pico.h"
-      "cppStandard": "c++11",
+            ],
-      "intelliSenseMode": "linux-gcc-arm",
+            "defines": [],
-      "configurationProvider": "ms-vscode.cmake-tools"
+            "compilerPath": "${userHome}/.pico-sdk/toolchain/14_2_Rel1/bin/arm-none-eabi-gcc.exe",
-    }
+            "compileCommands": "${workspaceFolder}/build/compile_commands.json",
-  ],
+            "cStandard": "c17",
-  "version": 4
+            "cppStandard": "c++14",
+            "intelliSenseMode": "linux-gcc-arm"
+        }
+    ],
+    "version": 4
 }

0x0017_constants/.vscode/cmake-kits.json

@@ -0,0 +1,15 @@
+[
+    {
+        "name": "Pico",
+        "compilers": {
+            "C": "${command:raspberry-pi-pico.getCompilerPath}",
+            "CXX": "${command:raspberry-pi-pico.getCxxCompilerPath}"
+        },
+        "environmentVariables": {
+            "PATH": "${command:raspberry-pi-pico.getEnvPath};${env:PATH}"
+        },
+        "cmakeSettings": {
+            "Python3_EXECUTABLE": "${command:raspberry-pi-pico.getPythonPath}"
+        }
+    }
+]

0x0017_constants/.vscode/extensions.json

@@ -1,9 +1,9 @@
 {
-  "recommendations": [
+    "recommendations": [
-    "marus25.cortex-debug",
+        "marus25.cortex-debug",
-    "ms-vscode.cmake-tools",
+        "ms-vscode.cpptools",
-    "ms-vscode.cpptools",
+        "ms-vscode.cpptools-extension-pack",
-    "ms-vscode.cpptools-extension-pack",
+        "ms-vscode.vscode-serial-monitor",
-    "ms-vscode.vscode-serial-monitor"
+        "raspberry-pi.raspberry-pi-pico"
-  ]
+    ]
-}
+}

0x0017_constants/.vscode/launch.json

@@ -1,58 +1,50 @@
 {
-  "version": "0.2.0",
+    "version": "0.2.0",
-  "configurations": [
+    "configurations": [
-    {
+        {
-      "name": "Pico Debug (Cortex-Debug)",
+            "name": "Pico Debug (Cortex-Debug)",
-      "cwd": "${workspaceFolder}",
+            "cwd": "${userHome}/.pico-sdk/openocd/0.12.0+dev/scripts",
-      "executable": "${command:cmake.launchTargetPath}",
+            "executable": "${command:raspberry-pi-pico.launchTargetPath}",
-      "request": "launch",
+            "request": "launch",
-      "type": "cortex-debug",
+            "type": "cortex-debug",
-      "servertype": "openocd",
+            "servertype": "openocd",
-      "gdbPath": "arm-none-eabi-gdb",
+            "serverpath": "${userHome}/.pico-sdk/openocd/0.12.0+dev/openocd.exe",
-      "device": "RP2040",
+            "gdbPath": "${command:raspberry-pi-pico.getGDBPath}",
-      "configFiles": [
+            "device": "${command:raspberry-pi-pico.getChipUppercase}",
-        "interface/cmsis-dap.cfg",
+            "configFiles": [
-        "target/rp2040.cfg"
+                "interface/cmsis-dap.cfg",
-      ],
+                "target/${command:raspberry-pi-pico.getTarget}.cfg"
-      "svdFile": "${env:PICO_SDK_PATH}/src/rp2040/hardware_regs/rp2040.svd",
+            ],
-      "runToEntryPoint": "main",
+            "svdFile": "${userHome}/.pico-sdk/sdk/2.2.0/src/${command:raspberry-pi-pico.getChip}/hardware_regs/${command:raspberry-pi-pico.getChipUppercase}.svd",
-      "openOCDLaunchCommands": [
+            "runToEntryPoint": "main",
-        "adapter speed 1000"
+            // Fix for no_flash binaries, where monitor reset halt doesn't do what is expected
-      ]
+            // Also works fine for flash binaries
-    },
+            "overrideLaunchCommands": [
-    {
+                "monitor reset init",
-      "name": "Pico Debug (Cortex-Debug with external OpenOCD)",
+                "load \"${command:raspberry-pi-pico.launchTargetPath}\""
-      "cwd": "${workspaceFolder}",
+            ],
-      "executable": "${command:cmake.launchTargetPath}",
+            "openOCDLaunchCommands": [
-      "request": "launch",
+                "adapter speed 5000"
-      "type": "cortex-debug",
+            ]
-      "servertype": "external",
+        },
-      "gdbTarget": "localhost:3333",
+        {
-      "gdbPath": "arm-none-eabi-gdb",
+            "name": "Pico Debug (Cortex-Debug with external OpenOCD)",
-      "device": "RP2040",
+            "cwd": "${workspaceRoot}",
-      "svdFile": "${env:PICO_SDK_PATH}/src/rp2040/hardware_regs/rp2040.svd",
+            "executable": "${command:raspberry-pi-pico.launchTargetPath}",
-      "runToEntryPoint": "main"
+            "request": "launch",
-    },
+            "type": "cortex-debug",
-    {
+            "servertype": "external",
-      "name": "Pico Debug (C++ Debugger)",
+            "gdbTarget": "localhost:3333",
-      "type": "cppdbg",
+            "gdbPath": "${command:raspberry-pi-pico.getGDBPath}",
-      "request": "launch",
+            "device": "${command:raspberry-pi-pico.getChipUppercase}",
-      "cwd": "${workspaceFolder}",
+            "svdFile": "${userHome}/.pico-sdk/sdk/2.2.0/src/${command:raspberry-pi-pico.getChip}/hardware_regs/${command:raspberry-pi-pico.getChipUppercase}.svd",
-      "program": "${command:cmake.launchTargetPath}",
+            "runToEntryPoint": "main",
-      "MIMode": "gdb",
+            // Fix for no_flash binaries, where monitor reset halt doesn't do what is expected
-      "miDebuggerPath": "arm-none-eabi-gdb",
+            // Also works fine for flash binaries
-      "miDebuggerServerAddress": "localhost:3333",
+            "overrideLaunchCommands": [
-      "debugServerPath": "openocd",
+                "monitor reset init",
-      "debugServerArgs": "-f interface/cmsis-dap.cfg -f target/rp2040.cfg -c \"adapter speed 1000\"",
+                "load \"${command:raspberry-pi-pico.launchTargetPath}\""
-      "serverStarted": "Listening on port .* for gdb connections",
+            ]
-      "filterStderr": true,
+        },
-      "stopAtEntry": true,
+    ]
-      "hardwareBreakpoints": {
-        "require": true,
-        "limit": 4
-      },
-      "preLaunchTask": "Flash",
-      "svdPath": "${env:PICO_SDK_PATH}/src/rp2040/hardware_regs/rp2040.svd"
-    }
-  ]
 }

0x0017_constants/.vscode/settings.json

@@ -1,29 +1,42 @@
 {
-    // These settings tweaks to the cmake plugin will ensure
+    "cmake.showSystemKits": false,
-    // that you debug using cortex-debug instead of trying to launch
+    "cmake.options.statusBarVisibility": "hidden",
-    // a Pico binary on the host
+    "cmake.options.advanced": {
-    "cmake.statusbar.advanced": {
+        "build": {
-        "debug": {
+            "statusBarVisibility": "hidden"
-            "visibility": "hidden"
         },
         "launch": {
-            "visibility": "hidden"
+            "statusBarVisibility": "hidden"
         },
-        "build": {
+        "debug": {
-            "visibility": "hidden"
+            "statusBarVisibility": "hidden"
-        },
-        "buildTarget": {
-            "visibility": "hidden"
         }
     },
-    "cmake.buildBeforeRun": true,
+    "cmake.configureOnEdit": false,
-    "cmake.configureOnOpen": true,
+    "cmake.automaticReconfigure": false,
-    "cmake.configureSettings": {
+    "cmake.configureOnOpen": false,
-      "CMAKE_MODULE_PATH": "${env:PICO_INSTALL_PATH}/pico-sdk-tools"
-    },
     "cmake.generator": "Ninja",
-    "C_Cpp.default.configurationProvider": "ms-vscode.cmake-tools",
+    "cmake.cmakePath": "${userHome}/.pico-sdk/cmake/v3.31.5/bin/cmake",
-    "C_Cpp.errorSquiggles": "enabled",
+    "C_Cpp.debugShortcut": false,
+    "terminal.integrated.env.windows": {
+        "PICO_SDK_PATH": "${env:USERPROFILE}/.pico-sdk/sdk/2.2.0",
+        "PICO_TOOLCHAIN_PATH": "${env:USERPROFILE}/.pico-sdk/toolchain/14_2_Rel1",
+        "Path": "${env:USERPROFILE}/.pico-sdk/toolchain/14_2_Rel1/bin;${env:USERPROFILE}/.pico-sdk/picotool/2.2.0-a4/picotool;${env:USERPROFILE}/.pico-sdk/cmake/v3.31.5/bin;${env:USERPROFILE}/.pico-sdk/ninja/v1.12.1;${env:PATH}"
+    },
+    "terminal.integrated.env.osx": {
+        "PICO_SDK_PATH": "${env:HOME}/.pico-sdk/sdk/2.2.0",
+        "PICO_TOOLCHAIN_PATH": "${env:HOME}/.pico-sdk/toolchain/14_2_Rel1",
+        "PATH": "${env:HOME}/.pico-sdk/toolchain/14_2_Rel1/bin:${env:HOME}/.pico-sdk/picotool/2.2.0-a4/picotool:${env:HOME}/.pico-sdk/cmake/v3.31.5/bin:${env:HOME}/.pico-sdk/ninja/v1.12.1:${env:PATH}"
+    },
+    "terminal.integrated.env.linux": {
+        "PICO_SDK_PATH": "${env:HOME}/.pico-sdk/sdk/2.2.0",
+        "PICO_TOOLCHAIN_PATH": "${env:HOME}/.pico-sdk/toolchain/14_2_Rel1",
+        "PATH": "${env:HOME}/.pico-sdk/toolchain/14_2_Rel1/bin:${env:HOME}/.pico-sdk/picotool/2.2.0-a4/picotool:${env:HOME}/.pico-sdk/cmake/v3.31.5/bin:${env:HOME}/.pico-sdk/ninja/v1.12.1:${env:PATH}"
+    },
+    "raspberry-pi-pico.cmakeAutoConfigure": true,
+    "raspberry-pi-pico.useCmakeTools": false,
+    "raspberry-pi-pico.cmakePath": "${HOME}/.pico-sdk/cmake/v3.31.5/bin/cmake",
+    "raspberry-pi-pico.ninjaPath": "${HOME}/.pico-sdk/ninja/v1.12.1/ninja",
     "files.associations": {
         "stdlib.h": "c"
     }

0x0017_constants/.vscode/tasks.json

@@ -1,29 +1,102 @@
 {
-  "version": "2.0.0",
+    "version": "2.0.0",
-  "tasks": [
+    "tasks": [
-    {
+        {
-      "label": "Flash",
+            "label": "Compile Project",
-      "type": "shell",
+            "type": "process",
-      "command": "openocd",
+            "isBuildCommand": true,
-      "args": [
+            "command": "${userHome}/.pico-sdk/ninja/v1.12.1/ninja",
-        "-f",
+            "args": ["-C", "${workspaceFolder}/build"],
-        "interface/cmsis-dap.cfg",
+            "group": "build",
-        "-f",
+            "presentation": {
-        "target/rp2040.cfg",
+                "reveal": "always",
-        "-c",
+                "panel": "dedicated"
-        "adapter speed 1000; program {${command:cmake.launchTargetPath}} verify reset exit"
+            },
-      ],
+            "problemMatcher": "$gcc",
-      "problemMatcher": []
+            "windows": {
-    },
+                "command": "${env:USERPROFILE}/.pico-sdk/ninja/v1.12.1/ninja.exe"
-    {
+            }
-      "label": "Build",
+        },
-      "type": "cmake",
+        {
-      "command": "build",
+            "label": "Run Project",
-      "problemMatcher": "$gcc",
+            "type": "process",
-      "group": {
+            "command": "${env:HOME}/.pico-sdk/picotool/2.2.0-a4/picotool/picotool",
-        "kind": "build",
+            "args": [
-        "isDefault": true
+                "load",
-      }
+                "${command:raspberry-pi-pico.launchTargetPath}",
-    }
+                "-fx"
-  ]
+            ],
+            "presentation": {
+                "reveal": "always",
+                "panel": "dedicated"
+            },
+            "problemMatcher": [],
+            "windows": {
+                "command": "${env:USERPROFILE}/.pico-sdk/picotool/2.2.0-a4/picotool/picotool.exe"
+            }
+        },
+        {
+            "label": "Flash",
+            "type": "process",
+            "command": "${userHome}/.pico-sdk/openocd/0.12.0+dev/openocd.exe",
+            "args": [
+                "-s",
+                "${userHome}/.pico-sdk/openocd/0.12.0+dev/scripts",
+                "-f",
+                "interface/cmsis-dap.cfg",
+                "-f",
+                "target/${command:raspberry-pi-pico.getTarget}.cfg",
+                "-c",
+                "adapter speed 5000; program \"${command:raspberry-pi-pico.launchTargetPath}\" verify reset exit"
+            ],
+            "problemMatcher": [],
+            "windows": {
+                "command": "${env:USERPROFILE}/.pico-sdk/openocd/0.12.0+dev/openocd.exe",
+            }
+        },
+        {
+            "label": "Rescue Reset",
+            "type": "process",
+            "command": "${userHome}/.pico-sdk/openocd/0.12.0+dev/openocd.exe",
+            "args": [
+                "-s",
+                "${userHome}/.pico-sdk/openocd/0.12.0+dev/scripts",
+                "-f",
+                "interface/cmsis-dap.cfg",
+                "-f",
+                "target/${command:raspberry-pi-pico.getChip}-rescue.cfg",
+                "-c",
+                "adapter speed 5000; reset halt; exit"
+            ],
+            "problemMatcher": [],
+            "windows": {
+                "command": "${env:USERPROFILE}/.pico-sdk/openocd/0.12.0+dev/openocd.exe",
+            }
+        },
+        {
+            "label": "RISC-V Reset (RP2350)",
+            "type": "process",
+            "command": "${userHome}/.pico-sdk/openocd/0.12.0+dev/openocd.exe",
+            "args": [
+                "-s",
+                "${userHome}/.pico-sdk/openocd/0.12.0+dev/scripts",
+                "-c",
+                "set USE_CORE { rv0 rv1 cm0 cm1 }",
+                "-f",
+                "interface/cmsis-dap.cfg",
+                "-f",
+                "target/rp2350.cfg",
+                "-c",
+                "adapter speed 5000; init;",
+                "-c",
+                "write_memory 0x40120158 8 { 0x3 }; echo [format \"Info : ARCHSEL 0x%02x\" [read_memory 0x40120158 8 1]];",
+                "-c",
+                "reset halt; targets rp2350.rv0; echo [format \"Info : ARCHSEL_STATUS 0x%02x\" [read_memory 0x4012015C 8 1]]; exit"
+            ],
+            "problemMatcher": [],
+            "windows": {
+                "command": "${env:USERPROFILE}/.pico-sdk/openocd/0.12.0+dev/openocd.exe",
+            }
+        }
+    ]
 }

0x0017_constants/0x0017_constants.c

@@ -0,0 +1,35 @@
+#include <stdio.h>
+#include <string.h>
+#include "pico/stdlib.h"
+#include "hardware/i2c.h"
+#include "lcd_1602.h"
+
+#define FAV_NUM 42
+
+#define I2C_PORT i2c1
+#define I2C_SDA_PIN 2
+#define I2C_SCL_PIN 3
+
+const int OTHER_FAV_NUM = 1337;
+
+int main(void) {
+    stdio_init_all();
+
+    i2c_init(I2C_PORT, 100000);
+    gpio_set_function(I2C_SDA_PIN, GPIO_FUNC_I2C);
+    gpio_set_function(I2C_SCL_PIN, GPIO_FUNC_I2C);
+    gpio_pull_up(I2C_SDA_PIN);
+    gpio_pull_up(I2C_SCL_PIN);
+
+    lcd_i2c_init(I2C_PORT, 0x27, 4, 0x08);
+
+    lcd_set_cursor(0, 0);
+    lcd_puts("Reverse");
+    lcd_set_cursor(1, 0);
+    lcd_puts("Engineering");
+
+    while (true) {
+        printf("FAV_NUM: %d\r\n", FAV_NUM);
+        printf("OTHER_FAV_NUM: %d\r\n", OTHER_FAV_NUM);
+    }
+}

0x0017_constants/CMakeLists.txt

@@ -1,21 +1,59 @@
+# Generated Cmake Pico project file
+
 cmake_minimum_required(VERSION 3.13)
 
-include(pico_sdk_import.cmake)
-project(0x0017_constant C CXX ASM)
 set(CMAKE_C_STANDARD 11)
 set(CMAKE_CXX_STANDARD 17)
+set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
 
+# Initialise pico_sdk from installed location
+# (note this can come from environment, CMake cache etc)
+
+# == DO NOT EDIT THE FOLLOWING LINES for the Raspberry Pi Pico VS Code Extension to work ==
+if(WIN32)
+    set(USERHOME $ENV{USERPROFILE})
+else()
+    set(USERHOME $ENV{HOME})
+endif()
+set(sdkVersion 2.2.0)
+set(toolchainVersion 14_2_Rel1)
+set(picotoolVersion 2.2.0-a4)
+set(picoVscode ${USERHOME}/.pico-sdk/cmake/pico-vscode.cmake)
+if (EXISTS ${picoVscode})
+    include(${picoVscode})
+endif()
+# ====================================================================================
+set(PICO_BOARD pico2 CACHE STRING "Board type")
+
+# Pull in Raspberry Pi Pico SDK (must be before project)
+include(pico_sdk_import.cmake)
+
+project(0x0017_constants C CXX ASM)
+
+# Initialise the Raspberry Pi Pico SDK
 pico_sdk_init()
 
-add_executable(0x0017_constant
+# Add executable. Default name is the project name, version 0.1
-    main.c
-)
 
-pico_enable_stdio_usb(0x0017_constant 1)
+add_executable(0x0017_constants 0x0017_constants.c lcd_1602.c)
-pico_enable_stdio_uart(0x0017_constant 1)
 
-pico_add_extra_outputs(0x0017_constant)
+pico_set_program_name(0x0017_constants "0x0017_constants")
+pico_set_program_version(0x0017_constants "0.1")
 
-target_link_libraries(0x0017_constant 
+# Modify the below lines to enable/disable output over UART/USB
+pico_enable_stdio_uart(0x0017_constants 1)
+pico_enable_stdio_usb(0x0017_constants 0)
+
+# Add the standard library to the build
+target_link_libraries(0x0017_constants
     pico_stdlib
+    hardware_i2c
+    hardware_gpio)
+
+# Add the standard include files to the build
+target_include_directories(0x0017_constants PRIVATE
+        ${CMAKE_CURRENT_LIST_DIR}
 )
+
+pico_add_extra_outputs(0x0017_constants)
+

0x0017_constants/lcd_1602.c

@@ -0,0 +1,114 @@
+/**
+ * @file lcd_1602.c
+ * @brief Implementation of PCF8574-backed HD44780 (16x2) LCD driver
+ * @author Kevin Thomas
+ * @date 2025
+ * 
+ * MIT License
+ * 
+ * Copyright (c) 2025 Kevin Thomas
+ * 
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ * 
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ * 
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#include "lcd_1602.h"
+#include <string.h>
+#include <stdint.h>
+
+static i2c_inst_t *lcd_i2c = NULL;
+static uint8_t lcd_addr = 0x27;
+static int lcd_nibble_shift = 4;
+static uint8_t lcd_backlight_mask = 0x08;
+
+/* PCF8574 -> LCD control pins */
+#define PIN_RS 0x01
+#define PIN_RW 0x02
+#define PIN_EN 0x04
+
+static void pcf_write_byte(uint8_t data) {
+    if (!lcd_i2c) return;
+    i2c_write_blocking(lcd_i2c, lcd_addr, &data, 1, false);
+}
+
+static void pcf_pulse_enable(uint8_t data) {
+    pcf_write_byte(data | PIN_EN);
+    sleep_us(1);
+    pcf_write_byte(data & ~PIN_EN);
+    sleep_us(50);
+}
+
+static void lcd_write4(uint8_t nibble, uint8_t mode) {
+    uint8_t data = (nibble & 0x0F) << lcd_nibble_shift;
+    data |= mode ? PIN_RS : 0;
+    data |= lcd_backlight_mask;
+    pcf_pulse_enable(data);
+}
+
+static void lcd_send(uint8_t value, uint8_t mode) {
+    lcd_write4((value >> 4) & 0x0F, mode);
+    lcd_write4(value & 0x0F, mode);
+}
+
+void lcd_i2c_init(i2c_inst_t *i2c, uint8_t pcf_addr, int nibble_shift, uint8_t backlight_mask) {
+    lcd_i2c = i2c;
+    lcd_addr = pcf_addr;
+    lcd_nibble_shift = nibble_shift;
+    lcd_backlight_mask = backlight_mask;
+
+    // Follow init sequence for HD44780 in 4-bit mode
+    lcd_write4(0x03, 0);
+    sleep_ms(5);
+    lcd_write4(0x03, 0);
+    sleep_us(150);
+    lcd_write4(0x03, 0);
+    sleep_us(150);
+    lcd_write4(0x02, 0);
+    sleep_us(150);
+
+    // Function set: 4-bit, 2 lines
+    lcd_send(0x28, 0);
+
+    // Display on, cursor off
+    lcd_send(0x0C, 0);
+
+    // Clear
+    lcd_send(0x01, 0);
+    sleep_ms(2);
+
+    // Entry mode set
+    lcd_send(0x06, 0);
+}
+
+void lcd_clear(void) {
+    lcd_send(0x01, 0);
+    sleep_ms(2);
+}
+
+void lcd_set_cursor(int line, int position) {
+    const uint8_t row_offsets[] = {0x00, 0x40};
+
+    if (line > 1) line = 1;
+    lcd_send(0x80 | (position + row_offsets[line]), 0);
+}
+
+void lcd_puts(const char *s) {
+    while (*s) {
+        lcd_send((uint8_t)*s++, 1);
+    }
+}

0x0017_constants/lcd_1602.h

@@ -0,0 +1,74 @@
+/**
+ * @file lcd_1602.h
+ * @brief Header for PCF8574-backed HD44780 (16x2) LCD driver
+ * @author Kevin Thomas
+ * @date 2025
+ * 
+ * MIT License
+ * 
+ * Copyright (c) 2025 Kevin Thomas
+ * 
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ * 
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ * 
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#ifndef LCD_1602_H
+#define LCD_1602_H
+
+#include <stdint.h>
+#include "pico/stdlib.h"
+#include "hardware/i2c.h"
+
+/**
+ * @brief Initialize the LCD driver over I2C
+ *
+ * Configures the internal driver state and performs the HD44780 initialization
+ * sequence. The driver does not configure I2C pins or call i2c_init; that
+ * must be done by the caller prior to calling this function.
+ *
+ * @param i2c Pointer to the I2C instance (e.g. i2c0 or i2c1)
+ * @param pcf_addr PCF8574 I2C address (commonly 0x27 or 0x3F)
+ * @param nibble_shift Bit shift applied to 4-bit nibbles (commonly 4 or 0)
+ * @param backlight_mask PCF8574 bit mask that controls the backlight
+ */
+void lcd_i2c_init(i2c_inst_t *i2c, uint8_t pcf_addr, int nibble_shift, uint8_t backlight_mask);
+
+/**
+ * @brief Clear the LCD display
+ *
+ * Clears the display and returns the cursor to the home position. This
+ * call blocks for the duration required by the HD44780 controller.
+ */
+void lcd_clear(void);
+
+/**
+ * @brief Set the cursor position
+ *
+ * @param line Line number (0 or 1)
+ * @param position Column (0..15)
+ */
+void lcd_set_cursor(int line, int position);
+
+/**
+ * @brief Write a null-terminated string to the display
+ *
+ * @param s The string to write (ASCII)
+ */
+void lcd_puts(const char *s);
+
+#endif // LCD_1602_H

0x0017_constants/main.c

@@ -1,15 +0,0 @@
-#include <stdio.h>
-#include "pico/stdlib.h"
-
-#define FAV_NUM 42
-
-const int OTHER_FAV_NUM = 1337;
-
-int main(void) {
-    stdio_init_all();
-
-    while (true) {
-        printf("FAV_NUM: %d\r\n", FAV_NUM);
-        printf("regular_fav_num: %d\r\n", OTHER_FAV_NUM);
-    }
-}

0x0017_constants/pico_sdk_import.cmake

@@ -3,6 +3,28 @@
 # This can be dropped into an external project to help locate this SDK
 # It should be include()ed prior to project()
 
+# Copyright 2020 (c) 2020 Raspberry Pi (Trading) Ltd.
+#
+# Redistribution and use in source and binary forms, with or without modification, are permitted provided that the
+# following conditions are met:
+#
+# 1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following
+# disclaimer.
+#
+# 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following
+# disclaimer in the documentation and/or other materials provided with the distribution.
+#
+# 3. Neither the name of the copyright holder nor the names of its contributors may be used to endorse or promote products
+# derived from this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+# INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+# DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+# SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+# WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+# THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
 if (DEFINED ENV{PICO_SDK_PATH} AND (NOT PICO_SDK_PATH))
     set(PICO_SDK_PATH $ENV{PICO_SDK_PATH})
     message("Using PICO_SDK_PATH from environment ('${PICO_SDK_PATH}')")
@@ -18,9 +40,20 @@ if (DEFINED ENV{PICO_SDK_FETCH_FROM_GIT_PATH} AND (NOT PICO_SDK_FETCH_FROM_GIT_P
     message("Using PICO_SDK_FETCH_FROM_GIT_PATH from environment ('${PICO_SDK_FETCH_FROM_GIT_PATH}')")
 endif ()
 
+if (DEFINED ENV{PICO_SDK_FETCH_FROM_GIT_TAG} AND (NOT PICO_SDK_FETCH_FROM_GIT_TAG))
+    set(PICO_SDK_FETCH_FROM_GIT_TAG $ENV{PICO_SDK_FETCH_FROM_GIT_TAG})
+    message("Using PICO_SDK_FETCH_FROM_GIT_TAG from environment ('${PICO_SDK_FETCH_FROM_GIT_TAG}')")
+endif ()
+
+if (PICO_SDK_FETCH_FROM_GIT AND NOT PICO_SDK_FETCH_FROM_GIT_TAG)
+  set(PICO_SDK_FETCH_FROM_GIT_TAG "master")
+  message("Using master as default value for PICO_SDK_FETCH_FROM_GIT_TAG")
+endif()
+
 set(PICO_SDK_PATH "${PICO_SDK_PATH}" CACHE PATH "Path to the Raspberry Pi Pico SDK")
 set(PICO_SDK_FETCH_FROM_GIT "${PICO_SDK_FETCH_FROM_GIT}" CACHE BOOL "Set to ON to fetch copy of SDK from git if not otherwise locatable")
 set(PICO_SDK_FETCH_FROM_GIT_PATH "${PICO_SDK_FETCH_FROM_GIT_PATH}" CACHE FILEPATH "location to download SDK")
+set(PICO_SDK_FETCH_FROM_GIT_TAG "${PICO_SDK_FETCH_FROM_GIT_TAG}" CACHE FILEPATH "release tag for SDK")
 
 if (NOT PICO_SDK_PATH)
     if (PICO_SDK_FETCH_FROM_GIT)
@@ -29,25 +62,40 @@ if (NOT PICO_SDK_PATH)
         if (PICO_SDK_FETCH_FROM_GIT_PATH)
             get_filename_component(FETCHCONTENT_BASE_DIR "${PICO_SDK_FETCH_FROM_GIT_PATH}" REALPATH BASE_DIR "${CMAKE_SOURCE_DIR}")
         endif ()
-        # GIT_SUBMODULES_RECURSE was added in 3.17
+        FetchContent_Declare(
-        if (${CMAKE_VERSION} VERSION_GREATER_EQUAL "3.17.0")
+                pico_sdk
-            FetchContent_Declare(
+                GIT_REPOSITORY https://github.com/raspberrypi/pico-sdk
-                    pico_sdk
+                GIT_TAG ${PICO_SDK_FETCH_FROM_GIT_TAG}
-                    GIT_REPOSITORY https://github.com/raspberrypi/pico-sdk
+        )
-                    GIT_TAG master
-                    GIT_SUBMODULES_RECURSE FALSE
-            )
-        else ()
-            FetchContent_Declare(
-                    pico_sdk
-                    GIT_REPOSITORY https://github.com/raspberrypi/pico-sdk
-                    GIT_TAG master
-            )
-        endif ()
 
         if (NOT pico_sdk)
             message("Downloading Raspberry Pi Pico SDK")
-            FetchContent_Populate(pico_sdk)
+            # GIT_SUBMODULES_RECURSE was added in 3.17
+            if (${CMAKE_VERSION} VERSION_GREATER_EQUAL "3.17.0")
+                FetchContent_Populate(
+                        pico_sdk
+                        QUIET
+                        GIT_REPOSITORY https://github.com/raspberrypi/pico-sdk
+                        GIT_TAG ${PICO_SDK_FETCH_FROM_GIT_TAG}
+                        GIT_SUBMODULES_RECURSE FALSE
+
+                        SOURCE_DIR ${FETCHCONTENT_BASE_DIR}/pico_sdk-src
+                        BINARY_DIR ${FETCHCONTENT_BASE_DIR}/pico_sdk-build
+                        SUBBUILD_DIR ${FETCHCONTENT_BASE_DIR}/pico_sdk-subbuild
+                )
+            else ()
+                FetchContent_Populate(
+                        pico_sdk
+                        QUIET
+                        GIT_REPOSITORY https://github.com/raspberrypi/pico-sdk
+                        GIT_TAG ${PICO_SDK_FETCH_FROM_GIT_TAG}
+
+                        SOURCE_DIR ${FETCHCONTENT_BASE_DIR}/pico_sdk-src
+                        BINARY_DIR ${FETCHCONTENT_BASE_DIR}/pico_sdk-build
+                        SUBBUILD_DIR ${FETCHCONTENT_BASE_DIR}/pico_sdk-subbuild
+                )
+            endif ()
+
             set(PICO_SDK_PATH ${pico_sdk_SOURCE_DIR})
         endif ()
         set(FETCHCONTENT_BASE_DIR ${FETCHCONTENT_BASE_DIR_SAVE})