new info

_blog/.hidden/reversing-soundbar-usb-protocol.md

@@ -0,0 +1,76 @@
+---
+slug: init-post
+title: Init post
+description: Init post
+date: "1970-01-01"
+hidden: true
+---
+
+## Init post
+Init post
+
+## How to sniff USB with usbmon and Wireshark
+The `usbmon` is a kernel module which is used to collect traces of I/O operations on the USB bus. It needs to be loaded.
+
+```bash
+# Load usbmon kernel module
+sudo modprobe usbmon
+
+# Check all loaded kernel modules
+lsmod
+```
+
+Now you can run Wireshark. To identify which USB device you want to sniff, you can use `lsusb` command. The **bus number** and the **device number** are essential. Every USB bus has its own number and it should be also available in the Wireshark menu as `usbmonX`. Example menu items:
+
+```bash
+enp5s0
+usbmon2 <--,
+usbmon1 <----- These are USB buses traffic
+usbmon0 <--'
+```
+
+Now you can sniff some USB traffic. Filter out the device you want to sniff: `usb.device_address == <device-number>`.
+
+## Get information about USB device
+An example output line of `lsusb` (list all USB devices) command:
+
+```text
+Bus 001 Device 008: ID 041e:3247 Creative Technology, Ltd Sound BlasterX Katana
+```
+
+Vendor ID = `041e`, Product ID = `3247`. To get more information about that specific device use: `lsusb -v -d <vendor-id>:<product-id>`.
+
+## Kernel modules
+Show kernel modules associated with USB devices: `lsusb -vt`.
+
+## Decoding SoundBlaster X Katana USB communication
+xxx
+
+Katana has no dedicated module and uses couple generic modules:
+
+* [usbhid](https://github.com/torvalds/linux/tree/master/drivers/hid/usbhid)
+
+## Problem with HID user-space drivers
+Theoretically the driver uses CONTROL transfer (to the Endpoint 0) in order to change Katana's volume level. Endpoint 0 is not directly connected with any USB interface, so it should be possible not to detach actual interface driver from the kernel. Unfortunately, without detaching, an "Resource busy" error occurs. Why is that?
+
+Katana uses CONTROL transfer indeed but with some special setup parameters:
+
+```text
+bmRequestType   = 0x21,
+bRequest        = 1,
+wValue          = 0x0201 (0x0202 in the second request),
+wIndex          = 256,
+```
+
+The `bmRequestType` parameter is a bit-field type:
+
+```text
+                           0x21 in binary
+
+       0                         01                 00001
+host-to-device (OUT)       class-specific         interface
+```
+
+I guess it has something to do with HID interface and because of that it doesn't work without detaching interface drivers. Unfortunately, the interfaces we have to disconnect interrupt the sound. I don't feel like implementing a whole audio driver just to change the volume. I was looking for an option to create some kind of "nested driver" that would use the default `snd-usb-audio` underneath, but would add my functionalities. I haven't found any sources on this. You'd probably have to rewrite the entire driver from scratch. The problem is that Katana uses the same interfaces to send audio and change volume level. Theoretically, it is possible to detach and reattach the driver after the script is executed, but of course `dev.attach_kernel_driver(x)` function doesn't work, so the project is stuck.
+
+Maybe I'll figure out some way of using the default `snd-usb-audio` driver underneath in the future.

_blog/.vscode/settings.json

@@ -0,0 +1,7 @@
+{
+    "editor.wordWrap": "on",
+    "[markdown]": {
+        "editor.wordWrap": "wordWrapColumn"
+    },
+    "editor.rulers": [80]
+}

_notes/bash/scripting.md

@@ -2,30 +2,49 @@
 title: Bash scripting notes
 ---
 
-## Differences between Bash and sh features
+- [1. Differences between Bash and sh features](#1-differences-between-bash-and-sh-features)
+  - [1.1. Major differences (Bash vs sh)](#11-major-differences-bash-vs-sh)
+- [2. Bash references](#2-bash-references)
+  - [2.1. Debugging (line by line)](#21-debugging-line-by-line)
+  - [2.2. Comments](#22-comments)
+  - [2.3. Special variables](#23-special-variables)
+  - [2.4. Prologue](#24-prologue)
+  - [2.5. Defining variables](#25-defining-variables)
+  - [2.6. If statement](#26-if-statement)
+  - [2.7. Loops](#27-loops)
+  - [2.8. Functions](#28-functions)
+  - [2.9. Strings](#29-strings)
+  - [2.10. Math / arithmetic](#210-math--arithmetic)
+  - [2.11. Arrays](#211-arrays)
+  - [2.12. Regex](#212-regex)
+  - [2.13. Quick tips](#213-quick-tips)
+
+## 1. Differences between Bash and sh features
 
 - [GNU Majo differences from the bourne shell](https://www.gnu.org/software/bash/manual/html_node/Major-Differences-From-The-Bourne-Shell.html)
 
 Bash is superset of sh. Sh is POSIX compliant, bash is not. Bash has many extra features which improve readability and speed of programming. Almost everything what does work on sh would be working on Bash as well, but not the other way.
 
-### Major differences (Bash vs sh)
+### 1.1. Major differences (Bash vs sh)
 
 ```bash
 if [[ ... ]] vs if [ ... ]
 ```
 
-## Bash references
+## 2. Bash references
 [Official Bash documentation (manual)](https://www.gnu.org/savannah-checkouts/gnu/bash/manual/bash.html)
 
-### Debugging (line by line)
+### 2.1. Debugging (line by line)
 
 ```bash
 # At the beginning of the script
 set -x
 trap read debug
 ```
 
-### Special variables
+### 2.2. Comments
+
+### 2.3. Special variables
 
 ```bash
 $?          # Exit code of last command
@@ -36,7 +55,7 @@ $@          # Array of arguments
 $$          # Current PID
 ```
 
-### Prologue
+### 2.4. Prologue
 
 ```bash
 #!/usr/bin/env bash                     # Shebang: run with Bash shell
@@ -54,7 +73,7 @@ set -e
 set -o pipefail                               
 ```
 
-### Defining variables
+### 2.5. Defining variables
 > **NOTE**: No spaces around equal sign!
 
 ```bash
@@ -67,7 +86,7 @@ var6=(1 5 9 43 23 43)                   # Array of numbers
 read var7                               # Read variable from stdin
 ```
 
-### If statement
+### 2.6. If statement
 
 ```bash
 # If statements (spaces around expression matter)
@@ -103,7 +122,7 @@ if [[ $v1 = $v2  || $v1 != $v3 ]]       # Or
 if [[ $v1 = $v2  && $v1 != $v3 ]]       # And
 ```
 
-### Loops
+### 2.7. Loops
 
 ```bash
 # For loops
@@ -116,13 +135,10 @@ done
 for file in /bin/*                      # Iterate over files
 for num in {1..12..2}                   # {start..end..step}
 for num in 1 9 4 3 3                    # Interate over list of items
+for item in "${arr[@]}"                 # Spread array to list of items (above)
 for (( i=0; i<5; i++ ))                 # C-like for loop
 for name in $(cat names.txt)            # Line by line output of a command
-
-# Iterate over array elements
-for item in "${arr[@]}"; do
-    echo "$item"
-done
+for arg in "$@"                         # Iterate over arguments
 
 # Iterate over lines of variable
 while read -r line; do
@@ -135,7 +151,7 @@ while read -r line; do
 done < file.txt
 ```
 
-### Functions
+### 2.8. Functions
 Arguments are not named. They are only positional. Same convention as for the
 script parameters.
 
@@ -148,7 +164,7 @@ function func1() {
 func1 "test-argument" 234               # Call a function
 ```
 
-### Strings
+### 2.9. Strings
 
 ```bash
 var='super'
@@ -170,14 +186,14 @@ str='1:2'
 IFS=: read -r var1 var2 <<< "$str"  =>  var1 == 1, var2 == 2 
 ```
 
-### Math / arithmetic
+### 2.10. Math / arithmetic
 
 ```bash
 $((1 + 1))                              # Math expression        
 $((x + y))                              # Variables math
 ```
 
-### Arrays
+### 2.11. Arrays
 
 ```bash
 arr=("1" "2" "3")                       # Define array
@@ -187,7 +203,7 @@ echo ${arr[3]}                          # Get item
 echo ${arr[@]}                          # Get all items
 ```
 
-### Regex
+### 2.12. Regex
 
 ```bash
 # Check matching and group extraction
@@ -197,3 +213,10 @@ if [[ $var1 =~ $exp ]]; then
     echo $BASH_REMATCH[1]               # First group
 fi
 ```
+
+### 2.13. Quick tips
+
+```bash
+echo $RANDOM                            # Get random number
+date +%s%N                              # Get UNIX timestamp (nanoseconds)
+```