umeter

umeter, FreeRTOS, SIM800L

Application API

HTTP packets (without SSL) with "Authorization" header
Authorization: payload HMAC SHA256 in base64 encoding

/api/time

GET
At startup, every 24 hours
Get current datetime

Response JSON:

Field	Type	Description
status	string	"ok" on success
ts	uint32	Current datetime (Unix timestamp)

/api/info

POST
At startup only
Send base device information

Request JSON:

Field	Type	Description
uid	uint32	Unique device ID
ts	uint32	Current datetime (Unix timestamp)
name	string	Device type
bl_git	string	Bootloader source revision
bl_status	uint32	Bootloader status
app_git	string	Application source revision
app_ver	uint32	Application version
mcu	string	MCU unique ID
apn	string	APN for cellular network
url_ota	string	OTA server URL
url_app	string	Application server URL
period_upload	uint32	Communication with application server period (seconds)
period_sensors	uint32	Sensors data update period (seconds)
period_anemometer	uint32	Measurement time for anemometer (seconds)

Response JSON:

Field	Type	Description
status	string	"ok" on success

/api/cnet

POST
At startup only
Send information about the nearest cellular base station

Request JSON:

Field	Type	Description
uid	uint32	Unique device ID
ts	uint32	Current datetime (Unix timestamp)
mcc	int32	Mobile Country Code
mnc	int32	Mobile Network Code
lac	int32	Location Area Code
cid	int32	Cell ID
lev	int32	The current signal strength (dBm)

Response JSON:

Field	Type	Description
status	string	"ok" on success

/api/data

POST Content-Type: application/octet-stream
Every period_upload seconds
Send device state and sensor measurements in compact binary format

Request body is raw binary (little-endian throughout):

Header (14 bytes)

Offset	Size	Type	Description
0	4	uint32	Unique device ID
4	4	uint32	Current datetime (Unix timestamp)
8	4	uint32	System uptime (FreeRTOS ticks)
12	1	uint8	Tamper input (0 or 1)
13	1	uint8	Number of sensor records (N)

Sensor record (20 bytes each, N records)

Offset	Size	Type	Description
0	4	uint32	Measurement datetime (Unix timestamp)
4	2	uint16	Battery voltage (mV)
6	2	int16	Temperature (0.01 °C)
8	2	uint16	Humidity (0.01 %RH)
10	2	uint16	Pressure (0.1 hPa)
12	2	uint16	Wind direction (0.01°)
14	2	uint16	Wind speed average (per period_anemometer seconds)
16	2	uint16	Wind speed minimum (per period_anemometer seconds)
18	2	uint16	Wind speed maximum (per period_anemometer seconds)

Total payload size: 14 + N × 20 bytes (max N = 50, max payload = 1014 bytes)

Response JSON:

Field	Type	Description
status	string	"ok" on success

Bootloader status

Status	Description
0	No new firmware
1	Successfully updated
2	Error: no external storage
3	Error: invalid firmware size
4	Error: invalid checksum (external storage)
5	Error: invalid checksum (internal memory)
6	Error: could not erase internal memory

OTA API

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Serial API

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Development setup

Init submodules:

git submodule init
git submodule update

Activate git hooks:

sh install-hooks.sh