fix: size CURRENT.UF2 from the app start, not from every block written

bank_0_size is measured from DFU_BANK_0_REGION_START by the CRC check and
by serial/OTA DFU, but msc_uf2.c recorded every UF2 block written from
0x1000 (so a CURRENT.UF2 restore, which carries the SoftDevice blocks,
overcounted by the SD span) and ghostfat.c used the value as a window
from USER_FLASH_START (so after a serial DFU the dump was short by the
same span - 1.2M instead of the real 1.5M+, and a restore of that dump
only works while the tail is still in flash).

Now ghostfat adds the SoftDevice span to bank_0_size, and msc_uf2 records
the highest app address written minus the app start.

Verified on RAK4631 with 2.8.0.abd3348 (729,528 B app): after a serial
DFU the dump is 1,762,304 B (SD span + app rounded to 256), and after
restoring that dump it is byte-identical and the same size.

Author: jamesarich

src/usb/msc_uf2.c

@@ -223,12 +223,15 @@ void tud_msc_write10_complete_cb(uint8_t lun)
         // update App
         update_status.status_code = DFU_UPDATE_APP_COMPLETE;
 
-        // Record the real written size so bootloader_settings.bank_0_size
+        // Record the real app span so bootloader_settings.bank_0_size
         // reflects the actual app, not 0 -- ghostfat.c's CURRENT.UF2 uses
-        // this to size its dump to the real app instead of the max region.
-        // 256 mirrors ghostfat.c's UF2_FIRMWARE_BYTES_PER_SECTOR (the UF2
-        // format's fixed payload-per-block size, not board-specific).
-        update_status.app_size = _wr_state.numWritten * 256;
+        // this to size its dump. Measured from DFU_BANK_0_REGION_START like
+        // serial/OTA DFU do, so a CURRENT.UF2 restore (which also carries
+        // the SoftDevice blocks) does not overcount.
+        if ( _wr_state.appEnd > DFU_BANK_0_REGION_START )
+        {
+          update_status.app_size = _wr_state.appEnd - DFU_BANK_0_REGION_START;
+        }
 
         PRINTF("Application update complete\r\n");
       }

src/usb/uf2/ghostfat.c

@@ -199,7 +199,14 @@ static uint32_t current_flash_size(void)
     bootloader_settings_t const * boot_setting;
     bootloader_util_settings_get(&boot_setting);
 
+    // bank_0_size counts from DFU_BANK_0_REGION_START (the CRC check and
+    // serial/OTA DFU both define it that way); the dump starts at
+    // USER_FLASH_START, so add the SoftDevice span in between.
     flash_sz = boot_setting->bank_0_size;
+    if ( flash_sz && (flash_sz != 0xFFFFFFFFUL) )
+    {
+      flash_sz += DFU_BANK_0_REGION_START - USER_FLASH_START;
+    }
 
     // Round up to a whole UF2 payload chunk, else the last real chunk of
     // the app would get truncated out of CURRENT.UF2.
@@ -484,6 +491,7 @@ int write_block (uint32_t block_no, uint8_t *data, WriteState *state)
       {
         PRINTF("Write addr = 0x%08lX, block = %ld (%ld of %ld)\r\n", bl->targetAddr, bl->blockNo, state->numWritten, bl->numBlocks);
         flash_nrf5x_write(bl->targetAddr, bl->data, bl->payloadSize, true);
+        if ( bl->targetAddr + bl->payloadSize > state->appEnd ) state->appEnd = bl->targetAddr + bl->payloadSize;
       }else if ( bl->targetAddr < USER_FLASH_START )
       {
         // do nothing if writing to MBR, occurs when SD hex is included

src/usb/uf2/uf2.h

@@ -52,6 +52,7 @@ SOFTWARE.
 typedef struct {
     uint32_t numBlocks;
     uint32_t numWritten;
+    uint32_t appEnd;          // highest end address written in app space (0 if none)
 
     bool aborted;             // aborting update and reset
     bool update_bootloader;   // if updating bootloader (else app)