protect ledger screen against burn in when baking

Makefile

@@ -25,7 +25,7 @@ GIT_DESCRIBE ?= $(shell git describe --tags --abbrev=8 --always --long --dirty 2
 VERSION_TAG ?= $(shell echo "$(GIT_DESCRIBE)" | cut -f1 -d-)
 APPVERSION_M=2
 APPVERSION_N=3
-APPVERSION_P=2
+APPVERSION_P=3
 APPVERSION=$(APPVERSION_M).$(APPVERSION_N).$(APPVERSION_P)
 
 # Only warn about version tags if specified/inferred

src/apdu_sign.c

@@ -563,6 +563,7 @@ size_t handle_apdu_sign_with_hash(uint8_t instruction) {
 static int perform_signature(bool const on_hash, bool const send_hash) {
 #ifdef BAKING_APP
     write_high_water_mark(&G.parsed_baking_data);
+    ux_empty_screen();
 #else
     if (on_hash && G.hash_only) {
         memcpy(G_io_apdu_buffer, G.final_hash, sizeof(G.final_hash));

src/ui.h

@@ -17,7 +17,9 @@ __attribute__((noreturn)) bool exit_app(
 __attribute__((noreturn)) void ux_confirm_screen(ui_callback_t ok_c, ui_callback_t cxl_c);
 
 void ux_idle_screen(ui_callback_t ok_c, ui_callback_t cxl_c);
-
+#ifdef BAKING_APP
+void ux_empty_screen();
+#endif
 /* Initializes the formatter stack. Should be called once before calling `push_ui_callback()`. */
 void init_screen_stack();
 /* User MUST call `init_screen_stack()` before calling this function for the first time. */

src/ui_empty.c

@@ -0,0 +1,60 @@
+#ifdef BAKING_APP
+#include "bolos_target.h"
+
+#include "ui.h"
+
+const bagl_element_t empty_screen_elements[] = {
+#if (BAGL_WIDTH == 128 && BAGL_HEIGHT == 64)
+    {{BAGL_RECTANGLE, 0x00, 0, 0, 128, 64, 0, 0, BAGL_FILL, 0x000000, 0xFFFFFF, 0, 0},
+     .text = NULL},
+#elif (BAGL_WIDTH == 128 && BAGL_HEIGHT == 32)
+    {{BAGL_RECTANGLE, 0x00, 0, 0, 128, 32, 0, 0, BAGL_FILL, 0x000000, 0xFFFFFF, 0, 0},
+     .text = NULL},
+#else
+#error "BAGL_WIDTH/BAGL_HEIGHT not defined"
+#endif
+    {{BAGL_LABELINE,
+      0x10,
+      6,
+      12,
+      116,
+      32,
+      0,
+      0,
+      0,
+      0xFFFFFF,
+      0x000000,
+      BAGL_FONT_OPEN_SANS_EXTRABOLD_11px | BAGL_FONT_ALIGNMENT_CENTER,
+      0},
+     .text = NULL}};
+
+typedef struct ux_layout_empty_params_s {
+    const char *line1;
+} ux_layout_empty_params_t;
+
+void ux_layout_empty_init(unsigned int stack_slot) {
+    ux_stack_init(stack_slot);
+    G_ux.stack[stack_slot].element_arrays[0].element_array = empty_screen_elements;
+    G_ux.stack[stack_slot].element_arrays[0].element_array_count = ARRAYLEN(empty_screen_elements);
+    G_ux.stack[stack_slot].element_arrays_count = 1;
+    G_ux.stack[stack_slot].button_push_callback = ux_flow_button_callback;
+    G_ux.stack[stack_slot].screen_before_element_display_callback = ux_layout_strings_prepro;
+    ux_stack_display(stack_slot);
+}
+
+void ux_layout_empty_screen_init(unsigned int whatever) {
+}
+
+void return_to_idle() {
+    ux_idle_screen(NULL, NULL);
+}
+
+UX_STEP_CB(empty_screen_step, empty, return_to_idle(), {" "});
+UX_STEP_INIT(empty_screen_border, NULL, NULL, { return_to_idle(); });
+UX_FLOW(ux_empty_flow, &empty_screen_step, &empty_screen_border, FLOW_LOOP);
+
+void ux_empty_screen() {
+    ux_flow_init(0, ux_empty_flow, NULL);
+}
+
+#endif

src/ui_nano_x.c

@@ -82,12 +82,22 @@ UX_STEP_NOCB(ux_variable_display,
              });
 UX_STEP_INIT(ux_init_lower_border, NULL, NULL, { display_next_state(false); });
 
+#if BAKING_APP
+UX_STEP_CB(ux_app_is_ready_step,
+           nn,
+           ux_empty_screen(),
+           {
+               "Application",
+               "is ready",
+           });
+#else
 UX_STEP_NOCB(ux_app_is_ready_step,
              nn,
              {
                  "Application",
                  "is ready",
              });
+#endif
 
 UX_STEP_CB(ux_idle_quit_step,
            pb,