docs: add documentation for gpio protocol

README.md

@@ -53,3 +53,49 @@ When `data_t` is copied, it checkes if the pointer to the measurements array is
 If both applies, it also copies the data from the array pointer to the kernel space.
 
 ### GPIO interface
+
+#### Physical Layer
+The protocol implements unidirectional serial communication over GPIO with the following characteristics:
+- Transmission rate: 9600 baud (104.17 microseconds per bit)
+- Signal levels: 
+  - Logical 0: GPIO Low
+  - Logical 1: GPIO High
+- Pin configuration: GPIO 575 as output
+
+#### Bit Transmission
+Bit transmission follows the UART-8N1 compatible format:
+1. Start bit: Logical 0 (Low)
+2. 8 data bits in LSB-first order
+3. Stop bit: Logical 1 (High)
+4. No parity checking
+5. No flow control
+
+#### Packet Structure
+A complete data `packet_t` consists of a header, variable measurement payload, and a CRC32 checksum field:
+
+#### Header (3 Bytes)
+1. Magic Number (1 byte)
+   - Fixed value: 0xAA
+   - Used for packet detection and synchronization
+2. Sender ID (1 byte)
+   - Identifies the sender
+3. Measurement Count (1 byte)
+   - Number of subsequent measurements
+   - Maximum value: 16 (MAX_MEASUREMENTS)
+
+#### Measurement Payload (10 bytes per measurement)
+For each `measurement_t`, the following fields are transmitted:
+1. Measurement Data (8 bytes)
+   - 64-bit measurement value
+   - The data is packed as a c-style union
+2. Measurement Type (1 byte)
+   - Data type of the measurement
+   - The following data types are available for a measurement: INT8, UINT8, INT16, UINT16, INT32, UINT32, INT64, UINT64, FLOAT32, FLOAT64
+
+3. Measurement ID (1 byte)
+   - Unique identifier for the measurement
+
+#### Trailer (4 bytes)
+- CRC32 checksum
+- Calculated over all preceding packet fields
+- Uses the Linux standard CRC32 algorithm