Add 0x03_button_cbm: bare-metal RP2350 button driver

- GPIO15 active-low button input with internal pull-up
- 20ms software debounce via busy-wait confirmation
- LED mirrors button state, UART reports edge transitions
- New gpio_config_input_pullup() in GPIO driver
- 1555B FLASH, 13 source files, zero warnings

drivers/0x03_button_cbm/Src/image_def.c

@@ -0,0 +1,35 @@
+/**
+  ******************************************************************************
+  * @file    image_def.c
+  * @author  Kevin Thomas
+  * @brief   RP2350 IMAGE_DEF block for boot ROM image recognition.
+  *
+  *          Must appear within the first 4 KB of flash for the boot ROM
+  *          to accept the image.
+  *
+  ******************************************************************************
+  * @attention
+  *
+  * Copyright (c) 2026 Kevin Thomas.
+  * All rights reserved.
+  *
+  * This software is licensed under terms that can be found in the LICENSE file
+  * in the root directory of this software component.
+  * If no LICENSE file comes with this software, it is provided AS-IS.
+  *
+  ******************************************************************************
+  */
+
+#include <stdint.h>
+
+/**
+  * @brief IMAGE_DEF block structure placed in flash
+  */
+__attribute__((section(".embedded_block"), used))
+const uint8_t picobin_block[] = {
+  0xD3, 0xDE, 0xFF, 0xFF,
+  0x42, 0x01, 0x21, 0x10,
+  0xFF, 0x01, 0x00, 0x00,
+  0x00, 0x00, 0x00, 0x00,
+  0x79, 0x35, 0x12, 0xAB
+};

drivers/0x03_button_cbm/Src/main.c

@@ -0,0 +1,94 @@
+/**
+  ******************************************************************************
+  * @file    main.c
+  * @author  Kevin Thomas
+  * @brief   Button demonstration: debounced press mirrors to LED + UART report.
+  *
+  *          Demonstrates GPIO input using the button driver. The onboard
+  *          LED mirrors the button state and every edge transition is
+  *          reported over UART.
+  *
+  *          Wiring:
+  *            GPIO15 -> One leg of push button
+  *            GND    -> Other leg of push button
+  *            GPIO25 -> Onboard LED (no external wiring needed)
+  *
+  ******************************************************************************
+  * @attention
+  *
+  * Copyright (c) 2026 Kevin Thomas.
+  * All rights reserved.
+  *
+  * This software is licensed under terms that can be found in the LICENSE file
+  * in the root directory of this software component.
+  * If no LICENSE file comes with this software, it is provided AS-IS.
+  *
+  ******************************************************************************
+  */
+
+#include "rp2350_button.h"
+#include "rp2350_led.h"
+#include "rp2350_uart.h"
+#include "rp2350_delay.h"
+
+#define DEBOUNCE_MS  20
+#define POLL_DELAY_MS 10
+
+/**
+  * @brief  Drive the LED to match the current button state.
+  * @param  pressed true if button is pressed, false if released
+  * @retval None
+  */
+static void _set_led_state(bool pressed)
+{
+  if (pressed)
+    led_on(LED_PIN);
+  else
+    led_off(LED_PIN);
+}
+
+/**
+  * @brief  Report a button edge transition over UART.
+  * @param  pressed    current button state
+  * @param  last_state pointer to the stored previous button state
+  * @retval None
+  */
+static void _report_edge(bool pressed, bool *last_state)
+{
+  if (pressed != *last_state) {
+    if (pressed)
+      uart_puts("Button: PRESSED\r\n");
+    else
+      uart_puts("Button: RELEASED\r\n");
+    *last_state = pressed;
+  }
+}
+
+/**
+  * @brief  Poll the button, mirror to LED, and report edges.
+  * @param  last_state pointer to the stored previous button state
+  * @retval None
+  */
+static void _poll_button(bool *last_state)
+{
+  bool pressed;
+  pressed = button_is_pressed(BUTTON_PIN);
+  _set_led_state(pressed);
+  _report_edge(pressed, last_state);
+}
+
+/**
+  * @brief  Application entry point for the button debounce demo.
+  * @retval int does not return
+  */
+int main(void)
+{
+  button_init(BUTTON_PIN, DEBOUNCE_MS);
+  led_init(LED_PIN);
+  uart_puts("Button driver initialized: button=GPIO15  led=GPIO25\r\n");
+  bool last_state = false;
+  while (1) {
+    _poll_button(&last_state);
+    delay_ms(POLL_DELAY_MS);
+  }
+}

drivers/0x03_button_cbm/Src/rp2350_button.c

@@ -0,0 +1,52 @@
+/**
+  ******************************************************************************
+  * @file    rp2350_button.c
+  * @author  Kevin Thomas
+  * @brief   Button input driver implementation for RP2350.
+  *
+  *          Configures a GPIO pin as an active-low input with internal
+  *          pull-up and provides debounced press detection using a
+  *          busy-wait confirmation delay.
+  *
+  ******************************************************************************
+  * @attention
+  *
+  * Copyright (c) 2026 Kevin Thomas.
+  * All rights reserved.
+  *
+  * This software is licensed under terms that can be found in the LICENSE file
+  * in the root directory of this software component.
+  * If no LICENSE file comes with this software, it is provided AS-IS.
+  *
+  ******************************************************************************
+  */
+
+#include "rp2350_button.h"
+#include "rp2350_gpio.h"
+#include "rp2350_delay.h"
+
+static uint32_t debounce_delay_ms = 20;
+
+/**
+  * @brief  Re-sample the pin after the debounce delay to confirm press.
+  * @param  pin GPIO pin number to re-sample
+  * @retval bool true if the pin is still low after the debounce delay
+  */
+static bool _debounce_confirm(uint32_t pin)
+{
+  delay_ms(debounce_delay_ms);
+  return !gpio_get(pin);
+}
+
+void button_init(uint32_t pin, uint32_t debounce_ms)
+{
+  debounce_delay_ms = debounce_ms;
+  gpio_config_input_pullup(pin);
+}
+
+bool button_is_pressed(uint32_t pin)
+{
+  if (!gpio_get(pin))
+    return _debounce_confirm(pin);
+  return false;
+}

drivers/0x03_button_cbm/Src/rp2350_coprocessor.c

@@ -0,0 +1,34 @@
+/**
+  ******************************************************************************
+  * @file    rp2350_coprocessor.c
+  * @author  Kevin Thomas
+  * @brief   Coprocessor access control driver implementation for RP2350.
+  *
+  *          Grants access to coprocessors 0 and 1 by setting the
+  *          corresponding bits in CPACR with DSB/ISB barriers.
+  *
+  ******************************************************************************
+  * @attention
+  *
+  * Copyright (c) 2026 Kevin Thomas.
+  * All rights reserved.
+  *
+  * This software is licensed under terms that can be found in the LICENSE file
+  * in the root directory of this software component.
+  * If no LICENSE file comes with this software, it is provided AS-IS.
+  *
+  ******************************************************************************
+  */
+
+#include "rp2350_coprocessor.h"
+
+void coprocessor_enable(void)
+{
+  uint32_t value;
+  value = *CPACR;
+  value |= (1U << CPACR_CP1_SHIFT);
+  value |= (1U << CPACR_CP0_SHIFT);
+  *CPACR = value;
+  __asm__ volatile ("dsb");
+  __asm__ volatile ("isb");
+}

drivers/0x03_button_cbm/Src/rp2350_delay.c

@@ -0,0 +1,39 @@
+/**
+  ******************************************************************************
+  * @file    rp2350_delay.c
+  * @author  Kevin Thomas
+  * @brief   Delay driver implementation for RP2350.
+  *
+  *          Busy-wait millisecond delay calibrated for a 14.5 MHz clock
+  *          (3600 loop iterations per millisecond).
+  *
+  ******************************************************************************
+  * @attention
+  *
+  * Copyright (c) 2026 Kevin Thomas.
+  * All rights reserved.
+  *
+  * This software is licensed under terms that can be found in the LICENSE file
+  * in the root directory of this software component.
+  * If no LICENSE file comes with this software, it is provided AS-IS.
+  *
+  ******************************************************************************
+  */
+
+#include "rp2350_delay.h"
+
+void delay_ms(uint32_t ms)
+{
+  if (ms == 0)
+    return;
+  __asm__ volatile (
+    "mov r4, #3600\n\t"
+    "mul r5, %0, r4\n\t"
+    "1:\n\t"
+    "subs r5, #1\n\t"
+    "bne 1b\n\t"
+    :
+    : "r" (ms)
+    : "r4", "r5", "cc"
+  );
+}

drivers/0x03_button_cbm/Src/rp2350_gpio.c

@@ -0,0 +1,112 @@
+/**
+  ******************************************************************************
+  * @file    rp2350_gpio.c
+  * @author  Kevin Thomas
+  * @brief   GPIO driver implementation for RP2350.
+  *
+  *          SIO-based GPIO configuration using IO_BANK0 and PADS_BANK0
+  *          register structs defined in rp2350.h. All register offsets
+  *          verified against the RP2350 datasheet (RP-008373-DS-2).
+  *
+  ******************************************************************************
+  * @attention
+  *
+  * Copyright (c) 2026 Kevin Thomas.
+  * All rights reserved.
+  *
+  * This software is licensed under terms that can be found in the LICENSE file
+  * in the root directory of this software component.
+  * If no LICENSE file comes with this software, it is provided AS-IS.
+  *
+  ******************************************************************************
+  */
+
+#include "rp2350_gpio.h"
+
+/**
+  * @brief  Configure pad control for a GPIO pin.
+  * @param  gpio_num GPIO pin number (0-29)
+  * @retval None
+  */
+static void _gpio_config_pad(uint32_t gpio_num)
+{
+  uint32_t value;
+  value = PADS_BANK0->GPIO[gpio_num];
+  value &= ~(1U << PADS_BANK0_OD_SHIFT);
+  value |= (1U << PADS_BANK0_IE_SHIFT);
+  value &= ~(1U << PADS_BANK0_ISO_SHIFT);
+  PADS_BANK0->GPIO[gpio_num] = value;
+}
+
+/**
+  * @brief  Set IO_BANK0 FUNCSEL to SIO for a GPIO pin.
+  * @param  gpio_num GPIO pin number (0-29)
+  * @retval None
+  */
+static void _gpio_config_funcsel(uint32_t gpio_num)
+{
+  uint32_t value;
+  value = IO_BANK0->GPIO[gpio_num].CTRL;
+  value &= ~IO_BANK0_CTRL_FUNCSEL_MASK;
+  value |= IO_BANK0_CTRL_FUNCSEL_SIO;
+  IO_BANK0->GPIO[gpio_num].CTRL = value;
+}
+
+/**
+  * @brief  Configure pad for input with pull-up enabled.
+  * @param  gpio_num GPIO pin number (0-29)
+  * @retval None
+  */
+static void _gpio_config_pad_input_pullup(uint32_t gpio_num)
+{
+  uint32_t value;
+  value = PADS_BANK0->GPIO[gpio_num];
+  value |= (1U << PADS_BANK0_IE_SHIFT);
+  value &= ~(1U << PADS_BANK0_ISO_SHIFT);
+  value |= (1U << PADS_BANK0_PUE_SHIFT);
+  value &= ~(1U << PADS_BANK0_PDE_SHIFT);
+  PADS_BANK0->GPIO[gpio_num] = value;
+}
+
+/**
+  * @brief  Enable the output driver for a GPIO pin via SIO.
+  * @param  gpio_num GPIO pin number (0-29)
+  * @retval None
+  */
+static void _gpio_enable_output(uint32_t gpio_num)
+{
+  SIO[SIO_GPIO_OE_SET_OFFSET] = (1U << gpio_num);
+}
+
+void gpio_config(uint32_t gpio_num)
+{
+  _gpio_config_pad(gpio_num);
+  _gpio_config_funcsel(gpio_num);
+  _gpio_enable_output(gpio_num);
+}
+
+void gpio_set(uint32_t gpio_num)
+{
+  SIO[SIO_GPIO_OUT_SET_OFFSET] = (1U << gpio_num);
+}
+
+void gpio_clear(uint32_t gpio_num)
+{
+  SIO[SIO_GPIO_OUT_CLR_OFFSET] = (1U << gpio_num);
+}
+
+void gpio_toggle(uint32_t gpio_num)
+{
+  SIO[SIO_GPIO_OUT_XOR_OFFSET] = (1U << gpio_num);
+}
+
+bool gpio_get(uint32_t gpio_num)
+{
+  return (SIO[SIO_GPIO_IN_OFFSET] & (1U << gpio_num)) != 0;
+}
+
+void gpio_config_input_pullup(uint32_t gpio_num)
+{
+  _gpio_config_pad_input_pullup(gpio_num);
+  _gpio_config_funcsel(gpio_num);
+}

drivers/0x03_button_cbm/Src/rp2350_led.c

@@ -0,0 +1,49 @@
+/**
+  ******************************************************************************
+  * @file    rp2350_led.c
+  * @author  Kevin Thomas
+  * @brief   LED driver implementation for RP2350.
+  *
+  *          High-level wrapper around the GPIO driver for LED control.
+  *
+  ******************************************************************************
+  * @attention
+  *
+  * Copyright (c) 2026 Kevin Thomas.
+  * All rights reserved.
+  *
+  * This software is licensed under terms that can be found in the LICENSE file
+  * in the root directory of this software component.
+  * If no LICENSE file comes with this software, it is provided AS-IS.
+  *
+  ******************************************************************************
+  */
+
+#include "rp2350_led.h"
+#include "rp2350_gpio.h"
+
+void led_init(uint32_t pin)
+{
+  gpio_config(pin);
+  gpio_clear(pin);
+}
+
+void led_on(uint32_t pin)
+{
+  gpio_set(pin);
+}
+
+void led_off(uint32_t pin)
+{
+  gpio_clear(pin);
+}
+
+void led_toggle(uint32_t pin)
+{
+  gpio_toggle(pin);
+}
+
+bool led_get_state(uint32_t pin)
+{
+  return gpio_get(pin);
+}

drivers/0x03_button_cbm/Src/rp2350_reset.c

@@ -0,0 +1,33 @@
+/**
+  ******************************************************************************
+  * @file    rp2350_reset.c
+  * @author  Kevin Thomas
+  * @brief   Reset controller driver implementation for RP2350.
+  *
+  *          Releases IO_BANK0 from reset and waits until the subsystem
+  *          is ready.
+  *
+  ******************************************************************************
+  * @attention
+  *
+  * Copyright (c) 2026 Kevin Thomas.
+  * All rights reserved.
+  *
+  * This software is licensed under terms that can be found in the LICENSE file
+  * in the root directory of this software component.
+  * If no LICENSE file comes with this software, it is provided AS-IS.
+  *
+  ******************************************************************************
+  */
+
+#include "rp2350_reset.h"
+
+void reset_init_subsystem(void)
+{
+  uint32_t value;
+  value = RESETS->RESET;
+  value &= ~(1U << RESETS_RESET_IO_BANK0_SHIFT);
+  RESETS->RESET = value;
+  while ((RESETS->RESET_DONE & (1U << RESETS_RESET_IO_BANK0_SHIFT)) == 0) {
+  }
+}

drivers/0x03_button_cbm/Src/rp2350_reset_handler.c

@@ -0,0 +1,45 @@
+/**
+  ******************************************************************************
+  * @file    rp2350_reset_handler.c
+  * @author  Kevin Thomas
+  * @brief   Reset handler implementation for RP2350.
+  *
+  *          Entry point after power-on or system reset. Initializes the
+  *          stack, XOSC, subsystem resets, UART, coprocessor, then
+  *          branches to main().
+  *
+  ******************************************************************************
+  * @attention
+  *
+  * Copyright (c) 2026 Kevin Thomas.
+  * All rights reserved.
+  *
+  * This software is licensed under terms that can be found in the LICENSE file
+  * in the root directory of this software component.
+  * If no LICENSE file comes with this software, it is provided AS-IS.
+  *
+  ******************************************************************************
+  */
+
+#include "rp2350_reset_handler.h"
+#include "rp2350_stack.h"
+#include "rp2350_xosc.h"
+#include "rp2350_reset.h"
+#include "rp2350_uart.h"
+#include "rp2350_coprocessor.h"
+
+extern int main(void);
+
+void __attribute__((naked, noreturn)) Reset_Handler(void)
+{
+  __asm__ volatile (
+    "bl stack_init\n\t"
+    "bl xosc_init\n\t"
+    "bl xosc_enable_peri_clk\n\t"
+    "bl reset_init_subsystem\n\t"
+    "bl uart_release_reset\n\t"
+    "bl uart_init\n\t"
+    "bl coprocessor_enable\n\t"
+    "b main\n\t"
+  );
+}

drivers/0x03_button_cbm/Src/rp2350_stack.c

@@ -0,0 +1,38 @@
+/**
+  ******************************************************************************
+  * @file    rp2350_stack.c
+  * @author  Kevin Thomas
+  * @brief   Stack pointer initialization for RP2350.
+  *
+  *          Sets MSP, PSP, MSPLIM, and PSPLIM using inline assembly.
+  *
+  ******************************************************************************
+  * @attention
+  *
+  * Copyright (c) 2026 Kevin Thomas.
+  * All rights reserved.
+  *
+  * This software is licensed under terms that can be found in the LICENSE file
+  * in the root directory of this software component.
+  * If no LICENSE file comes with this software, it is provided AS-IS.
+  *
+  ******************************************************************************
+  */
+
+#include "rp2350_stack.h"
+
+void stack_init(void)
+{
+  __asm__ volatile (
+    "ldr   r0, =%0\n\t"
+    "msr   PSP, r0\n\t"
+    "ldr   r0, =%1\n\t"
+    "msr   MSPLIM, r0\n\t"
+    "msr   PSPLIM, r0\n\t"
+    "ldr   r0, =%0\n\t"
+    "msr   MSP, r0\n\t"
+    :
+    : "i" (STACK_TOP), "i" (STACK_LIMIT)
+    : "r0"
+  );
+}

drivers/0x03_button_cbm/Src/rp2350_uart.c

@@ -0,0 +1,126 @@
+/**
+  ******************************************************************************
+  * @file    rp2350_uart.c
+  * @author  Kevin Thomas
+  * @brief   UART0 driver implementation for RP2350.
+  *
+  *          Configures UART0 on GPIO 0 (TX) and GPIO 1 (RX) at 115200
+  *          baud using the 14.5 MHz XOSC clock.
+  *
+  ******************************************************************************
+  * @attention
+  *
+  * Copyright (c) 2026 Kevin Thomas.
+  * All rights reserved.
+  *
+  * This software is licensed under terms that can be found in the LICENSE file
+  * in the root directory of this software component.
+  * If no LICENSE file comes with this software, it is provided AS-IS.
+  *
+  ******************************************************************************
+  */
+
+#include "rp2350_uart.h"
+
+#define UART_BASE ((volatile uint32_t *) UART0_BASE)
+
+/**
+  * @brief  Clear the UART0 reset bit in the reset controller.
+  * @retval None
+  */
+static void _uart_clear_reset_bit(void)
+{
+  uint32_t value;
+  value = RESETS->RESET;
+  value &= ~(1U << RESETS_RESET_UART0_SHIFT);
+  RESETS->RESET = value;
+}
+
+/**
+  * @brief  Wait until the UART0 block is out of reset.
+  * @retval None
+  */
+static void _uart_wait_reset_done(void)
+{
+  while ((RESETS->RESET_DONE & (1U << RESETS_RESET_UART0_SHIFT)) == 0) {
+  }
+}
+
+/**
+  * @brief  Configure GPIO pins 0 (TX) and 1 (RX) for UART function.
+  * @retval None
+  */
+static void _uart_configure_pins(void)
+{
+  IO_BANK0->GPIO[0].CTRL = IO_BANK0_CTRL_FUNCSEL_UART;
+  IO_BANK0->GPIO[1].CTRL = IO_BANK0_CTRL_FUNCSEL_UART;
+  PADS_BANK0->GPIO[0] = 0x04;
+  PADS_BANK0->GPIO[1] = 0x40;
+}
+
+/**
+  * @brief  Set UART0 baud rate divisors for 115200 at 14.5 MHz.
+  * @retval None
+  */
+static void _uart_set_baud(void)
+{
+  UART_BASE[UART_CR_OFFSET] = 0;
+  UART_BASE[UART_IBRD_OFFSET] = 6;
+  UART_BASE[UART_FBRD_OFFSET] = 33;
+}
+
+/**
+  * @brief  Configure line control and enable UART0.
+  * @retval None
+  */
+static void _uart_enable(void)
+{
+  UART_BASE[UART_LCR_H_OFFSET] = UART_LCR_H_8N1_FIFO;
+  UART_BASE[UART_CR_OFFSET] = UART_CR_ENABLE;
+}
+
+void uart_release_reset(void)
+{
+  _uart_clear_reset_bit();
+  _uart_wait_reset_done();
+}
+
+void uart_init(void)
+{
+  _uart_configure_pins();
+  _uart_set_baud();
+  _uart_enable();
+}
+
+bool uart_is_readable(void)
+{
+  return (UART_BASE[UART_FR_OFFSET] & UART_FR_RXFE_MASK) == 0;
+}
+
+char uart_getchar(void)
+{
+  while (UART_BASE[UART_FR_OFFSET] & UART_FR_RXFE_MASK) {
+  }
+  return (char)(UART_BASE[UART_DR_OFFSET] & 0xFF);
+}
+
+void uart_putchar(char c)
+{
+  while (UART_BASE[UART_FR_OFFSET] & UART_FR_TXFF_MASK) {
+  }
+  UART_BASE[UART_DR_OFFSET] = (uint32_t)c;
+}
+
+void uart_puts(const char *str)
+{
+  while (*str) {
+    uart_putchar(*str++);
+  }
+}
+
+char uart_to_upper(char c)
+{
+  if (c >= 'a' && c <= 'z')
+    return (char)(c - 32);
+  return c;
+}

drivers/0x03_button_cbm/Src/rp2350_xosc.c

@@ -0,0 +1,40 @@
+/**
+  ******************************************************************************
+  * @file    rp2350_xosc.c
+  * @author  Kevin Thomas
+  * @brief   XOSC driver implementation for RP2350.
+  *
+  *          Configures the external crystal oscillator and enables the
+  *          peripheral clock sourced from XOSC.
+  *
+  ******************************************************************************
+  * @attention
+  *
+  * Copyright (c) 2026 Kevin Thomas.
+  * All rights reserved.
+  *
+  * This software is licensed under terms that can be found in the LICENSE file
+  * in the root directory of this software component.
+  * If no LICENSE file comes with this software, it is provided AS-IS.
+  *
+  ******************************************************************************
+  */
+
+#include "rp2350_xosc.h"
+
+void xosc_init(void)
+{
+  XOSC->STARTUP = 0x00C4U;
+  XOSC->CTRL = 0x00FABAA0U;
+  while ((XOSC->STATUS & (1U << XOSC_STATUS_STABLE_SHIFT)) == 0) {
+  }
+}
+
+void xosc_enable_peri_clk(void)
+{
+  uint32_t value;
+  value = CLOCKS->CLK_PERI_CTRL;
+  value |= (1U << CLK_PERI_CTRL_ENABLE_SHIFT);
+  value |= (CLK_PERI_CTRL_AUXSRC_XOSC << CLK_PERI_CTRL_AUXSRC_SHIFT);
+  CLOCKS->CLK_PERI_CTRL = value;
+}

drivers/0x03_button_cbm/Src/vector_table.c

@@ -0,0 +1,38 @@
+/**
+  ******************************************************************************
+  * @file    vector_table.c
+  * @author  Kevin Thomas
+  * @brief   Vector table with initial stack pointer and reset handler.
+  *
+  *          Placed in the .vectors section at the start of flash.
+  *          The Thumb bit (bit 0 = 1) is automatically set by the
+  *          linker for function pointers in Thumb mode.
+  *
+  ******************************************************************************
+  * @attention
+  *
+  * Copyright (c) 2026 Kevin Thomas.
+  * All rights reserved.
+  *
+  * This software is licensed under terms that can be found in the LICENSE file
+  * in the root directory of this software component.
+  * If no LICENSE file comes with this software, it is provided AS-IS.
+  *
+  ******************************************************************************
+  */
+
+#include <stdint.h>
+
+extern uint32_t _stack_top;
+extern void Reset_Handler(void);
+
+typedef void (*vector_func_t)(void);
+
+/**
+  * @brief Vector table placed in .vectors section
+  */
+__attribute__((section(".vectors"), used))
+const void *_vectors[2] = {
+  &_stack_top,
+  Reset_Handler
+};