Add reversed protocol for TaiDoc TD-4277.

The device I have is branded GlucoRx Nexus, but multiple importers rebrand
this with different names, so file it with the manufacturer model number
instead.

README.md

@@ -29,6 +29,8 @@ contributors.
   - [OneTouch Verio (2015)](lifescan/onetouch-verio-2015.md)
 * SD Biosensor
   - [SD Codefree](sd-biosensor/codefree.md)
+* TaiDoc
+  - [TD-4277](taidoc/td4277.md)
 
 ## Structure
 

taidoc/td4277.md

@@ -0,0 +1,168 @@
+# TaiDoc TD-4277
+
+Reverse engineered by [Diego Elio Pettenò](mailto:[email protected]). With
+thanks to Gianni Ceccarelli for the time fields structure.
+
+This device is also known as:
+
+  * GlucoRx Nexus
+  * Menarini GlucoMen Nexus
+  * Aktivmed GlucoCheck XL
+
+## Important device notes
+
+The device has a miniUSB-A connector and comes with an onboard HID-to-Serial
+adapter, based on the Silicon Labs cp2110 interface.
+
+### USB IDs
+
+| Device         | Vendor ID | Product ID |
+| ---            | ---       | ---        |
+| GlucoRx Nexus  | 10c4      | ea80       |
+
+### Serial port configuration
+
+The CP2110 bridge should be configured as follows:
+
+  * 8 data bits;
+  * no parity bits;
+  * 1 stop bit;
+  * 19200 baud rate.
+
+### Supported Features
+
+The meter hardware supports:
+
+  * Factory-fixed mg/dL or mmol/L *user* reported unit. Values are always
+    returned by the protocol in mg/dL.
+  * Meal flags (none, pre-meal, post-meal).
+  * Sound and reminder alarms.
+
+## Protocol
+
+### Packet Structure
+
+The device uses a simple challenge and response serial protocol with fixed-size
+8-bytes commands and responses.
+
+    packet = STX command-id message direction checksum
+    STX = %x51
+
+    command-id = OCTET
+    message = 4OCTET
+    empty-message = %x00 %x00 %x00 %x00
+
+    direction = direction-in / direction-out
+    direction-in = %xA5
+    direction-out = %xA3
+
+    checksum = OCTET
+
+The checksum is calculated as a full sum of the first seven bytes of the packet,
+and then truncated to 8-bit.
+
+### Connection
+
+Connection is established by sending a connection command, and receiving a
+response.
+
+    message-connect = %x00
+    command-connect = %x22
+    response-connect = %x22 / %x24 / %x54
+
+In both the request and long  response packets, the message is zero.
+
+### Get Model
+
+To confirm the model of the device (probably to avoid confusing with other
+devices sharing a similar protocol), you can send command `0x24`.
+
+    model-request = STX %x24 empty-message direction-out checksum
+    model-response = STX %x24 model OCTET OCTET direction-in checksum
+
+    model = %x77 %x42  ; 16-bit little-endian value
+
+The model will be reported as a 16-bit little-endian BCD value.
+
+### Date and Time
+
+#### Format
+
+All representation of time for this protocol are idential, and they follow this
+format:
+
+    datetime = day minute hour
+    day = 2OCTET  ; 16-bit little endian value.
+    minute = OCTET
+    hour = OCTET
+
+While minutes and hours are left unpacked, the `day` field packs the full year,
+month and day into a single 16-bit integer.
+
+Within the 16-bit `day` field, the first 7 bits represent the year, starting
+with 2000, followed by 4 bits for the month (range 1-12), and 5 bits for the day
+(range 1-31).
+
+#### Getting Time
+
+To retrieve the time of the device, you send the command `0x23` with a zero
+message, and parse the returned message as the date and time.
+
+    gettime-request = STX %x23 empty-message direction-out checksum
+    gettime-response = STX %x23 datetime direction-in checksum
+
+#### Setting Time
+
+To set the time of the device, you send the command `0x33` with the time as
+message.
+
+    settime-request = STX %x33 datetime direction-out checksum
+    gettime-response = STX %x33 datetime direction-in checksum
+
+### Reading Records
+
+To retrieve the records from the device, you need to first request the number of
+records, and then retrieve the timestamp and the value and flags for each
+record.
+
+Record count and record index are 16-bit unsigned integers, little-endian, and
+are 0-indexed, with the most recent result first.
+
+    record-id = 2OCTET  ; 16-bit little-endian value
+
+#### Record Count
+
+To retrieve the record count, send command `0x2B`.
+
+    recordcount-request = STX %x2B empty-message direction-out checksum
+    recordcount-response STX %x2B record-count %x06 %x00 direction-in checksum
+
+    record-count = 2OCTET  ; 16-bit little-endian value
+
+#### Record Timestamp
+
+To retrieve each record timestamp, send command `0x25`.
+
+    record-timestamp-request = STX %x25
+                               record-id %x00 %x00 direction-out checksum
+    record-timestamp-response = STX %x25 datetime direction-in checksum
+
+#### Record Value
+
+To retrieve each record value, send command `0x26`.
+
+    record-value-request = STX %x26 record-id %x00 %x00 direction-out checksum
+    record-value-response = STX %x26
+                            glucose-value %x06 meal-flag direction-in checksum
+
+    glucose-value = 2OCTET  ; 16-bit little-endian value
+    meal-flag = meal-none / meal-before / meal-after
+    meal-none = %x00
+    meal-before = %x40
+    meal-after = %x80
+
+### Clearing Memory
+
+To completely clear the memory of the device, send command `0x52`.
+
+    clear-memory = STX %x52 empty-message direction-out checksum