small comment

README.md

@@ -2,9 +2,10 @@
 
 > [!NOTE]
 > **USBvalve Version 1.0.0**
+>
 > A complete rewrite of the application has been done:
 > - moved away from Arduino IDE environment, now the code is written for the [Pi Pico SDK](https://github.com/raspberrypi/pico-sdk)
-> - dependencies on external libraries has been reduced a lot
+> - dependencies on external libraries have been reduced a lot
 > - USB host support for Low Speed devices is now more robust (ATTiny85, EvilCrow, etc)
 > -  hardware and functionalities are almost unchanged, see the [notes](https://github.com/cecio/USBvalve#notes-about-bootsel-and-version--100) below for details 
 
@@ -82,7 +83,7 @@ The polling of BOOTSEL was creating some issues to the *BADUSB* detection so thi
 
 <img src="https://github.com/cecio/USBvalve/blob/main/pictures/reset_button.jpg" width="35%" height="35%" />
 
-~~In `PCB` you'll find also a version `1.3` of the board, with some holes on pads 1 and 3 to facilitate the mount of the button. But as you can see, you can also use your old version~~. (still waiting the new printed PCB to test it before publishing)
+In `PCB` you'll find also a version `1.3` of the board, with some holes on pads 1 and 3 to facilitate the mount of the button. But as you can see, you can also use your old version.
 
 If you are not using the *BADUSB* functions or if you prefer to have less coverage on detection but keep BOOTSEL usage, I'm also providing a firmware created with *bootsel* enabled (see folder and releases).
 
@@ -219,6 +220,9 @@ Obviously you can also build your own firmware. To build you need the *Raspberry
 Basic recompile instructions:
 ```
 export PICO_SDK_PATH=</path/to/pico-sdk>
+
+git clone --recursive https://github.com/cecio/USBvalve.git
+cd USBvalve
 mkdir build && cd build
 cmake -DPICO_BOARD=pico ..   # or pico2 for standard build
 make -j$(nproc)

src/usb_device.c

@@ -73,14 +73,17 @@ int32_t tud_msc_read10_cb(uint8_t lun, uint32_t lba, uint32_t offset,
         flag_autorun = true;
     }
 
-    // Protect memory: only read from real disk blocks
-    if (lba < DISK_BLOCK_NUM - 1) {
-        uint8_t const* addr = msc_disk[lba];
-        memcpy(buffer, addr, bufsize);
+    // Return data from ramdisk, or zeros for blocks beyond it.
+    // The disk reports FAKE_DISK_BLOCK_NUM sectors but only
+    // DISK_BLOCK_NUM exist in RAM, the rest must read as empty.
+    if (lba < DISK_BLOCK_NUM) {
+        memcpy(buffer, msc_disk[lba], bufsize);
+    } else {
+        memset(buffer, 0, bufsize);
     }
 
     serial_printf("Read LBA: %u   Size: %u\r\n", (unsigned)lba, (unsigned)bufsize);
-    if (lba < DISK_BLOCK_NUM - 1) {
+    if (lba < DISK_BLOCK_NUM) {
         hex_dump(msc_disk[lba], MAX_DUMP_BYTES);
     }
 
@@ -105,14 +108,13 @@ int32_t tud_msc_write10_cb(uint8_t lun, uint32_t lba, uint32_t offset,
         flag_written = true;
     }
 
-    // Protect memory: only write to real disk blocks
-    if (lba < DISK_BLOCK_NUM - 1) {
-        uint8_t* addr = msc_disk[lba];
-        memcpy(addr, buffer, bufsize);
+    // Only write to real disk blocks; silently discard beyond ramdisk
+    if (lba < DISK_BLOCK_NUM) {
+        memcpy(msc_disk[lba], buffer, bufsize);
     }
 
     serial_printf("Write LBA: %u   Size: %u\r\n", (unsigned)lba, (unsigned)bufsize);
-    if (lba < DISK_BLOCK_NUM - 1) {
+    if (lba < DISK_BLOCK_NUM) {
         hex_dump(msc_disk[lba], MAX_DUMP_BYTES);
     }