Fix missing slicing BD, add workaround for SD cards

UpdaterApp.cpp

@@ -37,10 +37,8 @@ int main()
 
     DigitalIn btn(DEMO_BUTTON);
 
-    // Use a buffered block device to allow arbitrary length writes to the underlying BD
     BlockDevice *secondary_bd = get_secondary_bd();
-    BufferedBlockDevice bufferedSecBD(secondary_bd);
-    int ret = bufferedSecBD.init();
+    int ret = secondary_bd->init();
     if (ret == 0) {
         tr_info("Secondary BlockDevice inited");
     } else {
@@ -58,21 +56,38 @@ int main()
     }
 
     tr_info("Erasing secondary BlockDevice...");
-    ret = bufferedSecBD.erase(0, bufferedSecBD.size());
+    ret = secondary_bd->erase(0, secondary_bd->size());
     if (ret == 0) {
         tr_info("Secondary BlockDevice erased");
     } else {
         tr_error("Cannot erase secondary BlockDevice: %d", ret);
     }
 
+    // Workaround: for block devices such as MicroSD cards where there is no fixed erase value,
+    // mcuboot will think that the "magic" region on the secondary BD, which it uses to store
+    // state info, is corrupt instead of simply not written yet.
+    // To fix this, we need to actually fill the last 40 bytes with 0xFFs.
+    if(secondary_bd->get_erase_value() == -1)
+    {
+        const std::vector<uint8_t> writeBuffer(40, 0xFF);
+        secondary_bd->program(writeBuffer.data(), secondary_bd->size() - 40, 40);
+    }
+
     tr_info("> Press button to copy update image to secondary BlockDevice");
 
     while(!DEMO_BUTTON_IS_PRESSED) {
         ThisThread::sleep_for(10ms);
     }
 
     // Copy the update image from internal flash to secondary BlockDevice
-    bufferedSecBD.program(&_binary_SimpleApp_update_image_bin_start, 0, SimpleApp_update_image_bin_length);
+    secondary_bd->program(&_binary_SimpleApp_update_image_bin_start, 0, SimpleApp_update_image_bin_length);
+
+    ret = secondary_bd->deinit();
+    if (ret == 0) {
+        tr_info("Secondary BlockDevice deinited");
+    } else {
+        tr_error("Cannot deinit secondary BlockDevice: %d", ret);
+    }
 
     // Activate the image in the secondary BlockDevice
     tr_info("> Image copied to secondary BlockDevice, press button to activate");

secondary_bd.cpp

@@ -9,6 +9,7 @@
 
 #include "SlicingBlockDevice.h"
 #include "FlashIAPBlockDevice.h"
+#include "BufferedBlockDevice.h"
 
 #if MBED_CONF_APP_SECONDARY_SLOT_IN_FLASH
 
@@ -35,9 +36,14 @@ mbed::BlockDevice* get_secondary_bd(void) {
     // If this assert fails, there is no block def
     MBED_ASSERT(default_bd != nullptr);
 
+    // mcuboot assumes that the read size of the secondary block device is the same as the read size
+    // of flash, so use a BufferedBlockDevice to wrap the underlying BD and ensure this is the case.
+    static mbed::BufferedBlockDevice buffered_bd(default_bd);
+
     // In this case, our flash is much larger than a single image so
     // slice it into the size of an image slot
-    //static mbed::SlicingBlockDevice sliced_bd(default_bd, 0x0, MCUBOOT_SLOT_SIZE);
-    return default_bd;
+    static mbed::SlicingBlockDevice sliced_bd(&buffered_bd, 0x0, MCUBOOT_SLOT_SIZE);
+
+    return &sliced_bd;
 }
 #endif