Add capability to force stay in DFU and erase app with button

This adds a check to see if a button is pressed. If the board button is pressed, stay if dfu mode.

Behavior is currently:

* If button is pressed at power up, enter DFU mode regardless of whether app is valid.
* If button is held longer than a timeout (Default 5 seconds), the app is erased.
* If button is released within the timeout period, the app is booted, if it's valid.

ports/mimxrt10xx/boards.c

@@ -39,6 +39,12 @@
 #include "tusb.h"
 #endif
 
+// allow board.h to change the pin configuration for the button
+#ifndef BUTTON_PIN_CONFIG
+// default to 22k pull up
+#define BUTTON_PIN_CONFIG ((1<<16) | (3<<14) | (1<<13) | (1<<12) | (4<<3))
+#endif
+
 static bool _dfu_mode = false;
 
 // needed by fsl_flexspi_nor_boot
@@ -80,11 +86,32 @@ void board_init(void)
   GPIO_PinInit(NEOPIXEL_PORT, NEOPIXEL_PIN, &neopixel_config);
 #endif
 
+#if TINYUF2_DFU_BUTTON
+  // Button
+  IOMUXC_SetPinMux( BUTTON_PINMUX, 1U);
+  IOMUXC_SetPinConfig(BUTTON_PINMUX, BUTTON_PIN_CONFIG);
+  gpio_pin_config_t button_config = { kGPIO_DigitalInput, 0, kGPIO_NoIntmode };
+  GPIO_PinInit(BUTTON_PORT, BUTTON_PIN, &button_config);
+  timer_set_ticks(0);
+  timer_start(1);
+  while(timer_uptime() < 20);
+  timer_stop();
+  timer_set_ticks(0);
+#endif
+
 #if TUF2_LOG
   board_uart_init(BOARD_UART_BAUDRATE);
 #endif
 }
 
+#if TINYUF2_DFU_BUTTON
+uint32_t board_button_read(void)
+{
+  uint32_t pressed = !!(BUTTON_STATE_ACTIVE == GPIO_PinRead(BUTTON_PORT, BUTTON_PIN));
+  return pressed;
+}
+#endif
+
 void board_teardown(void)
 {
   // no GPIO deinit for GPIO: LED, Neopixel, Button
@@ -241,8 +268,10 @@ void board_app_jump(void)
 
 void board_timer_start(uint32_t ms)
 {
-  // due to highspeed SystemCoreClock = 600 mhz, max interval of 24 bit systick is only 27 ms
-  const uint32_t tick = (SystemCoreClock/1000) * ms;
+  uint32_t tick = (SystemCoreClock/1000) * ms;
+  if (tick > SysTick_LOAD_RELOAD_Msk)
+      // if requesting too long an interval, just pick the longest we can support.
+      tick = SysTick_LOAD_RELOAD_Msk;
   SysTick_Config( tick );
 }
 
@@ -253,7 +282,7 @@ void board_timer_stop(void)
 
 void SysTick_Handler(void)
 {
-  board_timer_handler();
+    board_timer_handler();
 }
 
 //--------------------------------------------------------------------+

ports/mimxrt10xx/boards/imxrt1010_evk/board.h

@@ -69,6 +69,7 @@
 //--------------------------------------------------------------------+
 
 // SW8 button
+#define TINYUF2_DFU_BUTTON    1
 #define BUTTON_PINMUX         IOMUXC_GPIO_SD_05_GPIO2_IO05
 #define BUTTON_PORT           GPIO2
 #define BUTTON_PIN            5

src/board_api.h

@@ -98,6 +98,31 @@ void board_reset(void);
 // Write PWM duty value to LED
 void board_led_write(uint32_t value);
 
+#ifndef TINYUF2_DFU_BUTTON
+  #define TINYUF2_DFU_BUTTON 0
+#endif
+
+#if TINYUF2_DFU_BUTTON
+  // Read button.  Return a bitmask of which buttons are pressed.
+  uint32_t board_button_read(void);
+
+  // Hold the button for this many milliseconds to erase the app.
+  #ifndef TINYUF2_DFU_BUTTON_ERASE_TIMEOUT
+    #define TINYUF2_DFU_BUTTON_ERASE_TIMEOUT (5000)
+  #endif
+
+  // This is a bitmask used to check which button will cause a stay-in-dfu-mode
+  // default to use any button
+  // I'm somewhat unsure of how to deal with multiple buttons?
+  // perhaps instead of (or in addition to) board_button_read, there can be a 
+  // weak function called board_button_read_force_dfu() or something like that
+  // and that will leave the logic of when to enter the forced DFU mode up to 
+  // the individual boards.
+  #ifndef TINYUF2_DFU_BUTTON_FORCE_MASK
+    #define TINYUF2_DFU_BUTTON_FORCE_MASK 0xFFFFFFFF
+  #endif
+#endif
+
 // Write color to rgb strip
 void board_rgb_write(uint8_t const rgb[]);
 
@@ -251,10 +276,28 @@ enum {
   STATE_USB_UNPLUGGED,         ///< STATE_USB_UNPLUGGED
   STATE_WRITING_STARTED,       ///< STATE_WRITING_STARTED
   STATE_WRITING_FINISHED,      ///< STATE_WRITING_FINISHED
+  STATE_BUTTON_STAY_IN_DFU,    ///< STATE_BUTTON_STAY_IN_DFU
+  STATE_UNUSED,                ///< STATE_UNUSED
 };
 
+// Set the state of the app, including the indicators
 void indicator_set(uint32_t state);
 
+// Get the app state
+uint32_t indicator_get(void);
+
+// Start a timer with a tick of interval_ms
+void timer_start(uint32_t interval_ms);
+
+// top the timer
+void timer_stop(void);
+
+// Set the current tick count
+void timer_set_ticks(uint32_t ticks);
+
+// get uptime in ms.  Currently, this isn't counted when the timer is stopped.
+uint32_t timer_uptime(void);
+
 static inline void rgb_brightness(uint8_t out[3], uint8_t const in[3], uint8_t brightness)
 {
   for(uint32_t i=0; i<3; i++ )