WITRN Protocol

Works with WITRN C4/C4L/C5, A2, U3 series

Protocol Layer

• USB HID

Packet Structures

The USBPac is sent at a fixed rate as long as the meter is connected to the USB. the sampling rate depends on the Host's rotation rate rather than the meter's USBPac sending rate

---

USBPac

The most basic packet structure, transmitted via HID Data. Each packet starts with a fixed "start" and "head"

struct USBPac {
	byte start; // 0xFF
	byte head; 	// 0x55
	byte idx1;
	byte idx2;
	byte needAck;
	// USBPac.<free>e__FixedBuffer free; // bytes[3]
	bytes[3] free;
	USBSPac pac;
	byte verify;
}

start byte	head byte	idx1 byte	idx2 byte	needAck byte	free 3 bytes	pac 55 bytes	verify byte
FF	55	Any	Any	Any	Any	Structure	Any

• start

  Fixed, 0xFF

   p->start = byte.MaxValue;

• head

  Fixed, 0x55

   p->head = 85;

• idx1

  Seconds part of the timing

   p->idx1 = (byte)(time / 1000U);

• idx2

  Millisecond part of the timing

   p->idx2 = (byte)(time % 1000U);

• needAck

  When this request needs to be replied to. For example, if host requests the version or serial number of a meter, it will get the data in the response

  Specify by the flag bit

   if (bneedAck) {
   	p->needAck = (byte)(time / 30U | 128U);
   } else {
   	p->needAck = (byte)(time / 30U & 127U);
   }

  If a reply is required, it will follow a read process after sending the data

   if (this.SendPac(&pac, 1000) == sizeof(USBPac)) {
   	if (bNeedAck) {
   		Mem.memset((void*)(&pac), 0, sizeof(USBPac));
   		if (!this.beInAutoReadMode) {
   			if (this.ReadPac(&pac, timeout) == sizeof(USBPac) && Transef.usb_decodeUsbPac(&pac) && pac.pac.command == command) {
   				Mem.memcpy(prev, (void*)(&pac.pac.buf.FixedElementField), (int)readSize);
   				res = true;
   			}
   		}
   		else if (this.ReadAsyn(&pac, command, timeout, timeStart) == sizeof(USBPac)) {
   			Mem.memcpy(prev, (void*)(&pac.pac.buf.FixedElementField), (int)readSize);
   			res = true;
   		}
   	}
   	else {
   		res = true;
   	}
   }

• free

  Some time-related data. No specific use is identified

  p->free.FixedElementField = (byte)(time / 100U);
  *(ref p->free.FixedElementField + 1) = (byte)(time % 100U);
  *(ref p->free.FixedElementField + 2) = (byte)(time / 80U);

• pac

  Structure, see USBSPac. Valid data section

• verify

  Check digits

  public unsafe static byte getUsbPacSum(USBPac* p) {
  	return Transef.getUsbSPacSum(&p->pac) + p->start + p->head + p->idx1 + p->idx2 + p->free.FixedElementField + *(ref p->free.FixedElementField + 1) + *(ref p->free.FixedElementField + 2) + p->needAck;
  }

---

USBSPac

pac field of USBPac. Used for sending commands from the host side to the meter side, or reporting data from the meter side to the host

struct USBSPac {
	byte command;
	byte length;
	// USBSPac.<buf>e__FixedBuffer buf; // bytes[52]
	bytes[52] buf; // MeterData
	byte verify;
}

command byte	length byte	buf 52 bytes	verify byte
Any	Any	Structure	Any

• command

  No specific use is identified

• length

  buf Length

• buf

  Data to be sent by the host to the meter side, or data reported by the meter side

  • Data sent from the host to the meter side

    Known usage cases are to get the table firmware version, serial number

  • Data reported by the meter side

    Structure，see MeterData。Valid data section

• verify

  Check digits

   public unsafe static byte getUsbSPacSum(USBSPac* p) {
   	byte verify = 0;
   	for (int idx = 0; idx < sizeof(USBSPac) - 1; idx++) {
   		verify += *(byte*)(p + idx / sizeof(USBSPac));
   	}
   	return verify;
   }

---

MeterData

buf field of USBSPac. Data reported by the meter side

struct MeterData {
	byte OffPer;
	byte OffHour;
	ushort RecmA;
	float Ah;
	float Wh;
	uint RecTime;
	uint RunTime;
	float dp;
	float dm;
	float TempIn;
	float TempOut;
	float vol;
	float cur;
	byte RecGrp;
	// public MeterData.<reseverd>e__FixedBuffer reseverd; // bytes[7]
	bytes[7] reseverd;
}

OffPer byte	OffHour byte	RecmA ushort	Ah float	Wh float	RecTime uint	RunTime uint	dp float	dm float	TempIn float	TempOut float	vol float	cur float	RecGrp byte	reseverd 7 byte
Any	Any	Any	Any	Any	Any	Any	Any	Any	Any	Any	Any	Any	Any	Any

• OffPer

  No specific use is identified

• OffHour

  No specific use is identified

• RecmA

  No specific use is identified

• Ah

  Recorded capacity since the beginning

• Wh

  Recorded energy since the beginning

• RecTime

  Time elapsed since start of recording

• RunTime

  Time elapsed since start of running

• dp

  Data Positive (D+) Voltage

• dm

  Data Negative (D-) Voltage

• TempIn

  Temperature of input direction

• TempOut

  Temperature of output direction

• vol

  Real-time voltage

• cur

  Real-time current

• RecGrp

  Current data group

• reseverd

  Unused

---

Demo

demo.py