[SC64][DOCS] Updated documentation

docs/03_usb_interface.md

@@ -43,6 +43,9 @@
     - [`arg0` (type)](#arg0-type)
     - [`arg1` (length)](#arg1-length-2)
     - [`data` (data)](#data-data-1)
+  - [`D`: **DD\_SET\_BLOCK\_READY**](#d-dd_set_block_ready)
+    - [`arg0` (error)](#arg0-error)
+  - [`W`: **WRITEBACK\_ENABLE**](#w-writeback_enable)
 - [Asynchronous packets](#asynchronous-packets)
   - [`B`: **BUTTON**](#b-button)
   - [`U`: **DATA**](#u-data)
@@ -146,7 +149,7 @@ Available packet IDs are listed in the [asynchronous packets](#asynchronous-pack
 ## Supported commands
 
 | id  | name                                            | arg0         | arg1          | data | response         | description                                                   |
-| --- | --------------------------------------- | ------------ | ------------- | ---- | ---------------- | ------------------------------------------------------------- |
+| --- | ----------------------------------------------- | ------------ | ------------- | ---- | ---------------- | ------------------------------------------------------------- |
 | `v` | [**IDENTIFIER_GET**](#v-identifier_get)         | ---          | ---           | ---  | identifier       | Get flashcart identifier `SCv2`                               |
 | `V` | [**VERSION_GET**](#v-version_get)               | ---          | ---           | ---  | version          | Get flashcart firmware version                                |
 | `R` | [**STATE_RESET**](#r-state_reset)               | ---          | ---           | ---  | ---              | Reset flashcart state (CIC params and config options)         |
@@ -160,8 +163,8 @@ Available packet IDs are listed in the [asynchronous packets](#asynchronous-pack
 | `m` | [**MEMORY_READ**](#m-memory_read)               | address      | length        | ---  | data             | Read data from specified memory address                       |
 | `M` | [**MEMORY_WRITE**](#m-memory_write)             | address      | length        | data | ---              | Write data to specified memory address                        |
 | `U` | [**USB_WRITE**](#u-usb_write)                   | type         | length        | data | N/A              | Send data to be received by app running on N64 (no response!) |
-| `D` | **DD_SET_BLOCK_READY**                  | success      | ---           | ---  | ---              | Notify flashcart about 64DD block readiness                   |
-| `W` | **WRITEBACK_ENABLE**                    | ---          | ---           | ---  | ---              | Enable save writeback through USB packet                      |
+| `D` | [**DD_SET_BLOCK_READY**](#d-dd_set_block_ready) | error        | ---           | ---  | ---              | Notify flashcart about 64DD block readiness                   |
+| `W` | [**WRITEBACK_ENABLE**](#w-writeback_enable)     | ---          | ---           | ---  | ---              | Enable save writeback through USB packet                      |
 | `p` | **FLASH_WAIT_BUSY**                             | wait         | ---           | ---  | erase_block_size | Wait until flash ready / Get flash block erase size           |
 | `P` | **FLASH_ERASE_BLOCK**                           | address      | ---           | ---  | ---              | Start flash block erase                                       |
 | `f` | **FIRMWARE_BACKUP**                             | address      | ---           | ---  | status/length    | Backup firmware to specified memory address                   |
@@ -274,6 +277,8 @@ Use this command to get value of config option. Available config options are lis
 | -------- | ------------ |
 | `[31:0]` | Config value |
 
+_This command does not send response data._
+
 Use this command to set value of config option. Available config options are listed [here](./04_config_options.md).
 
 ---
@@ -310,6 +315,8 @@ Use this command to get value of persistent setting option. Available persistent
 | -------- | ------------- |
 | `[31:0]` | Setting value |
 
+_This command does not send response data._
+
 Use this command to set value of persistent setting option. Available persistent setting options are listed [here](./04_config_options.md).
 
 ---
@@ -440,6 +447,37 @@ If N64 acknowledge the request, then data is written to the flashcart memory to
 
 ---
 
+### `D`: **DD_SET_BLOCK_READY**
+
+**Notify flashcart about 64DD block readiness**
+
+#### `arg0` (error)
+| bits     | description                |
+| -------- | -------------------------- |
+| `[31:1]` | _Unused_                   |
+| `[0]`    | `0` - Success, `1` - Error |
+
+_This command does not send response data._
+
+This command informs SC64 that 64DD disk block data was successfully (or not) read to the requested buffer or written to the 64DD disk file.
+This command must be sent for each incoming [**DISK_REQUEST**](#d-disk_request) asynchronous packet.
+
+---
+
+### `W`: **WRITEBACK_ENABLE**
+
+**Enable save writeback through USB packet**
+
+_This command does not require arguments or data._
+
+_This command does not send response data._
+
+This command is used to enable save writeback module and set its mode to send data to the USB interface instead of writing to the SD card.
+To disable save writeback change save type via [**SAVE_TYPE**](./04_config_options.md#6-save_type) config option (setting the same save type as currently enabled will also disable writeback module).
+Save data is sent via [**SAVE_WRITEBACK**](#s-save_writeback) asynchronous packet.
+
+---
+
 ## Asynchronous packets
 
 | id  | name                                    | data                 | description                                                           |