--- a/FontPack/base_upperRegion.c	Mon Jan 01 18:56:14 2018 +0100
+++ b/FontPack/base_upperRegion.c	Mon Jan 01 20:12:34 2018 +0100
@@ -36,10 +36,16 @@
 
 /* Includes ------------------------------------------------------------------*/
 
+// From Common/Inc:
 #include "FirmwareData.h"
+
+// From Discovery/Inc
 #include "gfx_fonts.h"
 
-#include "stm32f4xx_hal.h"
+// From AC6 support:
+#include <stdio.h>
+
+//////////////////////////////////////////////////////////////////////////////
 
 const SFirmwareData font_FirmwareData   __attribute__(( section(".upper_firmware_data") )) =
 {
@@ -66,6 +72,8 @@
     .magic[3] = FIRMWARE_MAGIC_END
 };
 
+//////////////////////////////////////////////////////////////////////////////
+
 /* Fonts fixed in upper region */
 #include "Fonts/font_awe48.h"
 #include "Fonts/font_T24.h"
@@ -81,8 +89,111 @@
 #include "Fonts/image_heinrichs_weikamp.h"
 #include "Fonts/image_ostc.h"
 
+//////////////////////////////////////////////////////////////////////////////
+
+static int errors = 0;
+#define ASSERT(e) \
+    do { if( ! (e) ) {++errors; printf("FAIL at %3d: %s", __LINE__, #e);}} while(0)
+
+#define ASSERT_RANGE(e, min, max) \
+    ASSERT(min <= e); ASSERT( e <= max)
+
 int main(void)
 {
+    //---- Check the linker puts the directory at the requested address ------
+    ASSERT( & Awe48    == (tFont*)0x8100000 );
+    ASSERT( & FontT24  == (tFont*)0x810000c );
+    ASSERT( & FontT42  == (tFont*)0x8100018 );
+    ASSERT( & FontT48  == (tFont*)0x8100024 );
+    ASSERT( & FontT54  == (tFont*)0x8100030 );
+    ASSERT( & FontT84  == (tFont*)0x810003c );
+    ASSERT( & FontT105 == (tFont*)0x8100048 );
+    ASSERT( & FontT144 == (tFont*)0x8100052 );
+
+    //---- Check the linker puts the font data in the requested section ------
+    extern tChar __upper_font_data;
+    extern tChar __upper_font_data_end;
+    ASSERT( &__upper_font_data == (tChar*)0x08132040 );
+    ASSERT_RANGE( (int)&__upper_font_data_end, 0x08132040, 0x081E0000);
+
+    //---- Walk through the directory data -----------------------------------
+    extern const tFont __font_directory;
+    extern const tFont __font_directory_end;
+    for(const tFont* font = & __font_directory; font < &__font_directory_end; ++font)
+    {
+        // Check END-OF-DIRECTORY magic marker
+        if( font->length == (uint32_t)-1 )
+        {
+            ASSERT( font == &FontT144 + 1 );
+            break;
+        }
+
+        // Check font descriptors are inside a safe range.
+        ASSERT_RANGE( font->length,               10, 103 );
+        ASSERT_RANGE( font->spacesize,             0,  18 );
+        ASSERT_RANGE( font->spacesize2Monospaced, 13,  72 );
+        ASSERT_RANGE( font->height,               28, 108 );
+
+        //---- Walk through each char ----------------------------------------
+        for(int i = 0; i < font->length; ++i)
+        {
+            const tChar* c = &font->chars[i];
+
+            // Check char data is indeed stored in the actual data section
+            ASSERT_RANGE( c, &__upper_font_data, &__upper_font_data_end);
+
+            // Check char data sanity
+            ASSERT_RANGE( c->code, 0x0000, 0xF143);
+
+            // Check image sanity
+            const tImage* image = c->image;
+            ASSERT_RANGE(image,  (tImage*)&__upper_font_data, (tImage*)&__upper_font_data_end);
+            ASSERT_RANGE(image->width, font->spacesize, font->spacesize2Monospaced);
+            ASSERT(image->height == font->height);
+
+            // Uncompress image bytes
+            const uint8_t* byte = image->data;
+            ASSERT_RANGE(byte,  (uint8_t*)&__upper_font_data, (uint8_t*)&__upper_font_data_end);
+
+            for(int w=0; w <image->width; ++w)
+            {
+                // Compression: special 0x01 byte at start of column means just skip it.
+                if( *byte++ == 0x01 )
+                    continue;
+
+                int zeros = (byte[-1] == 0x00) ? 1 : 0;
+                for(int h = 1; h < image->height; ++h)
+                {
+                    if( *byte == 0x00 )
+                        ++zeros;
+
+                    // Other bytes cannot have the 0x01 value...
+                    ASSERT( *byte++ != 0x01 );
+                }
+
+                if( zeros == image->height )
+                    printf("Font[%d] char[%d]: could skip column %d",
+                            &__font_directory - font, i, w);
+            }
+
+            // Check the byte stream do not collide with the next char,
+            // or with the first tImage struct of the font.
+            if( (i+1) < font->length )
+                ASSERT( byte < font->chars[i+1].image->data );
+            else
+                ASSERT( byte < (uint8_t*)font->chars[0].image );
+
+            // TODO: check image bytes are contiguous between chars.
+        }
+    }
+
+    if( errors )
+    {
+        printf("Font Check: %d errors.", errors);
+        return -1;
+    }
+
+    printf("Font Check: no errors.");
     return 0;
 }