From July, 2021, new BACRouter had a hardware revision for improving EMI, but that cause incompatibility with old firmware.
Some users keep using version 2.18, so we provide version 2.19 firmware which is compatible with old hardware and has same features with version 2.18.
From version 4.09, the firmware is compatible with old hardware, but user can not downgrade to prior firmware on new hardware.
BASgatewayLX (Hereinafter referred to as LX) supports CSV configuration file. There are decent documents about the format and dozens of configuration samples for vary devices on their website. The convert tool we provided could convert the CSV file to JSON file which could be imported in BACRounter’s WebUI to create a Modbus slave station.
Matters need attention:
Though LX claims the object name should be unique, but the accessory “Profile Checker” does not check duplicated object name. We found a lots duplicated object names in the samples. So we decided to disable object with duplicated name in converting.
Some CSV files have characters out of UTF8 code page, we guess they are ISO-8859-1 encoding. So if we fail to decode CSV by UTF8, we fall back to ISO-8859-1.
LX supports maximum 64 bytes of object name and description (With ISO-8859-1 encoding?). BACRouter supports 64 bytes too, but with UTF8 encoding. There has possibility that 64 bytes in ISO-8859-1 is larger than 64 bytes when encoding as UTF8. We will tail-cut too long name and description and promote to user.
BACRouter doesn’t allow 2 output objects mapped to overlapped Modbus address, but LX seems to allow it. We will disable the conflicted object in converting.
LX defines register order for every 32 bits data, but BACRouter has to set unitary byte order for all objects. If the consistent byte order definitions are found when converting, the previous definition will be accepted, the conflict will be promoted to user.
BACRouter has object instance range of 0~999 for every slave, but LX seems no limitation. If instance larger than 999 is found, the object will be auto assigned a new instance.
From firmware v4.x，Offline configuration had been introduced. Now user could configure a BACRouter without device on hand, then export configuration to a file. When commissioning on the field, user just need to import previously exported file, “Save&Reboot” to take effect the configuration.
From v4.04，The object definitions for Modbus gateway could be import/export as CSV format. User could effectively setup object to Modbus address mapping In batches with Excel/WPS/Libreoffice, then import it to WebUI for detailed modify.
Download and extract it to disk, open index.html by your web browser (Because IE/Edge doesn’t support Local Storage for file:// URL, the user library for binary text and most used engineering unit will not be kept after leaving the web page)
There are 3 types of configuration file:
BACRouter Configuration File
This type of configuration file keeps all settings in BACRouter. If the firmware version of exporting one is same to importing one, WebUI should not complain of the configuration file.
Modbus Master Configuration File
This type of configuration file keeps setting under the scope of Modbus master. When importing it, collision detecting logic based on current mapping mode will check every enabled slave in this master, if collision is found, the slave will be disabled.
If the master is RTU/ASCII type, it may also be disabled if there are contention for RS485 port.
With these problem, WebUI will prompt user to re-check configuration.
Modbus Slave Configuration File
This type of configuration file keeps setting under the scope of Modbus slave. When importing it, if collision detecting logic based on current mapping mode found problem, the slave will be disabled.
It is allowed to import TCP salve configuration file in RTU/ASCII master, and vice versa, but the slave may be disabled if Modbus parameter setting do not work.
With these problem, WebUI will prompt user to re-check configuration.
Update on 2021-06-07 for version 4.05
From firmware version 4.x, BACRouter has builtin Modbus gateway functionality. This article will try to explain the underlying mechanism.
BACRouter will periodically read point’s value and cache it. “Update interval” defines how often BACRouter update the value.
To improve performance, BACRouter will read as more as possible data in one transcation. In Modbus standard, at most 2000 bits (coil or discrete) or 125 registers (input or holding register) could be read in one request, but specific Modbus slave device may only support a lower value. In BACRouter’s WebUI, there is a Modbus parameter edit dialog in “Slave Settings”, “Multiply read bits” and “Multiply read registers” parameters define the ability of the slave device.
BACRouter will not segment reading of single point even the “Multiply read registers” is less than registers used by the point.
Usually the data we care for has discontinuous Modbus address, for example, We only care for coils on address 1 and 2000, though we could read coil data from address 1 to 2000 in one request and skip returned data from address 2 to 1999, sending two requests independently for coil on address 1 and coil on address 2000 maybe more efficient. “Bits skipped” and “Registers skipped” parameter define how many unused data units between 2 cared data units are allowed to be skipped. As previous example, if “Bits skipped” is set to 1998, the BACRouter will try to read coil 1 and 2000 in single request. If “Bits skipped” is set to 1997, then BACRouter will read Coil 1 first, then Coil 2000, because bits skipped is 1998 and is greater than the setting of 1997.
On the WebUI page for slave, the “Read Group” button will show how the BACRouter will group the reading and test it. User should pay special attention on server exception of “Illegal data address”.
BACRouter will not combine multiple writing demand into one writing request. It always queue write request immediately after receiving command.
For writing single data unit, there are two Modbus function codes available. For example, function code 5 is writing single coil, function code 15 is writing multiple coils but the quantity of coil to write could be assigned to 1. Some devices only support one of them. “Coil write singly” parameter will specify which function code is used.
In the same way, “Register write singly” is applied to register writing. If any BACnet output object maps to multiple holding registers, it implies the slave device support function code 16 for write multiple registers, function code 16 will be used for writing any register whatever “Register write singly” is set.
If any read/write request failed, BACRouter will retry it, when the continuous fail count reachs 3, BACRouter will regard the slave device as offline. In offline state, BACRouter will retry the request every “Offline update interval”.
The BACnet side reaction for offline event will be described later.
Modbus Serial Bus
BACRouter supports serial slave devices with different baudrate, parity, RTU/ASCII mode on same RS485 bus. Before sending request, BACRouter will change it serial port parameter based on slave device’s settings.
It should be safe to have 2 devices with same slave address but different baudrate or RTU/ASCII mode, but preventing collision based on different parity might not be enough, because some devices do not examine parity error.
Single Device Mapping Mode
If VBUS network port is not enabled, BACRouter will work in single device mapping mode, every Modbus slave device will be mapped into exclusive object instance space of 1000 in the only BACnet device defined in “Application Settings”.
The actual BACnet object name will be organized as “master_name|slave_name|object_name”, The delimiter “|” is select-able by user.
As recommended by standard, BACRouter will create one StructuredView object for each slave device.
When the slave device turn to offline in this mode, all points’ reliability will be set to “COMMUNICATION_FAILURE”, if slave device is back to online, upon updating of point value, the point’s reliability will be set back to “NO_FAULT_DETECTED”.
Virtual Device Mapping Mode
If VBUS network port is enabled. Each slave device will be mapped to a virtual BACnet device on VBUS network. The MAC address will start from 1.
In this mode, each slave shall has a unique “Device instance”. The actual device name will be “master_name|slave_name”, The delimiter “|” is select-able.
When the slave device turn to offline in this mode, as recommended by standard, the virtual BACnet device will stop sending/receiving any packet to simulate offline state. if slave device is back to online, after updating all point’s value, the virtual BACnet device will quite offline state.
Slave Device’s Status
For every slave device, BACRouter will create 3 objects in gateway device, one object is Binary_Input with name of “online”, which represents online/offline status of slave device. another object is Analog_Input with name of “update_delay”, which is recently average update time delayed over “”Update interval”, the last one is Analog_Input with name of “fail_rate”, which count a relative long time fail rate on Modbus side.
Those objects’ name have prefix of “master_name|slave_name|comm|”, where “|” is select-able delimiter.
Object Instance Assignment
Object Instance is defined for every object. When the editor dialog for a object is submitted and the object is enabled, the object instance claimed by the object will be assigned, if that assigning fail, a automatically selected instance will be used.
AV/BV/MV is behaving same as AI/BI/MI, except that when AV/BV/MV is mapped to writable Modbus address (0X or 4X), the present value of the object is writable, the writing will be forwarded to Modbus side.
The value of output object is still being polled from Modbus side and set to object’s Relinguish_Default property. If the value read back does not match last value written, BACRouter will set the reliability of that object to “UNRELIABLE_OTHER”, and BACRouter will queue another write after a certain time.
Because of above verifying mechanism, the BACRouter will prevent defining two output objects with overlaping Modbus writable address.
NaN For Float And Double
NaN is a special value defined by IEEE-754, BACRouter does not accept NaN (Infinite is still valid for BACRouter).
When a point is defined as Float and Double, but NaN is read from slave, BACRouter will set the reliability to “UNRELIABLE_OTHER”.
Original BACnet MS/TP data link specification only supports NPDU length up to 501 bytes, which is much shorter than 1497 bytes of Ethernet and IP data link. It limits transmission performance, increases complexity on application layer, especial when two IP/Ethernet networks are conjoined by a MS/TP network.
Extended frame was designed to solve this problem. The detail could be found here. Briefly, this addendum added two new frame types as:
- 32: BACnet Extended Data Expecting Reply
- 33: BACnet Extended Data Not Expecting Reply
Frame type 32 is extended from frame type 5 (BACnet Data Expecting Reply), the special of it is that it is encoded by COBS and the NPDU length it carried is in range of 502 to 1497 bytes.
In the same way, frame type 33 is extended from frame type 6 (BACnet Data Not Expecting Reply)
Extended frame support was added into BACnet standard since revision 16. There are still lot of devices installed or on the market that do not support it. The interoperability between extended frame capable devices and legacy device is discussed below.
- Non-router legacy device and extended frame capable device: Because all messages sent to legacy device are application layer message, the “Max APDU Length Accepted” from Device object property or confirmed service request primitive should be respected, the NPDU length will not exceed 501 bytes. So there are no problem with this configuration.
- Legacy router and extended frame capable device: NPDU that should be relayed to other network through legacy router with length over 501 bytes will be discarded, no reject-message-to network with reason “Message Too Long” will be responded. Even more, the “Max APDU Length Accepted” of legacy router may be determined by other port that has a NPDU length larger than 501 bytes (It is allowed by standard), so NPDU for local application layer sent to legacy router will still possibly be carried by extended frame and discarded. So this configuration may cause problem in field.
BACRouter supports extended frame from very early version. From firmware version 3.18, we introduced “Extended frame” option on BACRouter’s MS/TP configuration, if there are legacy router that does not support extended frame on the bus, this option should be disabled to avoid Interoperability issues.
It’s worth noting that even “Extended frame” option is disabled, unlike legacy router, BACRouter will still be interoperable with extended frame capable devices.
（Screenshot has been updated on Aug 5, 2021. Because extended frame is mandatory from standard revision 16, from firmware 4.13, we move this option to extended configure mode.)
There are 2 types of BACnet service: unconfirmed and confirmed. The sender(client) of confirmed service request will wait for reply until timeout expires.
Usually there are no side effect of excess message delay for unconfirmed service. For confirmed service request or reply, excess message delay will result in poor network performance, because the service reply will be dropped by client due to timeout.
Furthermore, too late reply for confirmed service will cause application logic wrong. Each confirmed service request has a invokeID, the reply message carries same invokeID. The value range of invokeID is 0~255. On a busy client, the invokeID will be exhausted and re-used soon. if the invokeID of a delayed confirmed service reply is re-used by another service, the reply will be regarded as replying to later one. For exmaple:
- Client send WriteProperty service A to device X object Y property Z. The invokeID is 0. The request or reply messages is delayed.
- Client waits until timeout expires. Service A fails so invokeID 0 is reclaimed.
- Client send WriteProperty service B to device X object U property V. The invokeID 0 is chosed.
- Reply for service A is arrived, because its invokeID is same as service B, client believes that service B success.
For high speed data link type as Ethernet or IP, the message delay is neglect-able, but for MSTP, there are several possible reasons for excess message delay:
- Signal noise.
- Incorrect/improper device configuration(baudrate, max-master, max_info_frames)
- Excess traffic.
- Slow device
To avoid invokeID conflict and improve network performance, BACRouter with firmware version >=2.0 implements message delay guarantee of 10 seconds. Messages which could not be sent within 10 seconds will be dropped by BACRouter.
Update on 2020-11-20 (Appended info. about JCI module)
MSTP baudrate is always painful for field technician. If the baudrate is wrong, device can’t join a MSTP bus.
Most devices have fixed baudrate. To modify the baudrate setting, technician have to physically access the device and change dip switches. Some devices support changing baudrate by BACnet service. but before that they should already have correctly baudrate setting for BACnet service to access it.
Some vendors implement auto baudrate, but introduce more problem than it solves. There are two types of auto baudrate mechanism:
- Starting detection: The device detects and adopts baudrate on the bus when it starts. then never changes baudrate.
- Dynamic detection: The device does same as starting detection type when it starts, but if it find there are error on bus for a predefined time, it considers that the baudrate is changed, it detects baudrate again.
For both types, it is difficult to change baudrate when devices is working. Simply changing baudrate on all fixed baudrate devices can not work, because auto baudrate devices are still working on old baudrate. The solution is to power off all auto baudrate devices, then power on all auto baudrate devices（Don’t power off/on auto baudrate devices one by one)
Our new firmware(>=2.0) introduces new baudrate management mechanism(Patent pending). There are 3 types of baudrate mode for BACRouter : Fixed/Auto/Force:
- Fixed baudrate mode works as most traditional devices.
- Auto baudrate mode is same as above-mentioned dynamic detection. The predefined time to re-initiate detection is 10 error frames, it usually take several seconds.
- Forced baudrate mode is same as auto mode except that when the device get token, it changes baudrate to predefined value.
When there is a device with forced baudrate mode, the baudrate on the bus will be forced to predefined value. Devices with auto baudrate mode will automatically synchronize to predefined baudrate. Devices with fixed baudrate mode but baudrate setting different with predefined value will not be seen on bus (It’s easy to check out in “Recent active devices” field from BACRouter’s runtime info). Devices with starting detection type may run on wrong baudrate, they will not be seen on bus too, but powering off/on them one by one will synchronize them to forced value.
More than one device with forced baudrate mode could coexist on a bus, but the baudrate values on them should be same.
JCI FEC/IOM modules implements baudrate dynamic detection mechanism, the re-detect interval is about 150 sec on the test.
On a test bus , BACRouter cooperate perfectly with FEC2611, IOM3731, the baudrate is dynamically controlled by BACRouter from 9.6k ~ 76.8k, FEC2611 and IOM3731 will catch up after 2.5 minutes.
From firmware ver2.0, BACRouter introduced new “Max_info_frames by token occupy time” feature.
In BACnet standard of MSTP, a master device could hold token until it has sent frames up to Max_info_frames. The default value of Max_info_frames is 1. But for router, this value may be increased to improve bandwidth between networks. Mostly the suggested value for router is between 5 to 20.
MSTP works as a field bus for controllers; sensors and actuators. The data exchanging latency between devices usually should be guaranteed. We recommend devices get token at least every 1 second.
The APDUs passing router usually have size between 10~50 bytes, but could be up to 480 or 1476 (Extended frame). Larger APDU need more time to send or receive.
For APDU which need a reply from targeted device, router has to wait for reply. Usually the targeted device need more time to handle or generate larger APDU, router has to wait longer.
So the time router holding token could be varied much, which impacts latency guaranty of MSTP bus. To avoid this problem, “Max_info_frames by token occupy time” feature limits router’s token holding time.
The limitation is calculated by:
byte_time * 32 * Max_info_frames
For example, Max_info_frames is set to 10. The baud rate is 76800bps, so the byte_time is 0.13 milliseconds:
0.13 * 32 * 10 = 41.6 milliseconds.
When router founds it have held token for 41.6 milliseconds, it passes token to next station, though the frames it sent may be less than 10.
This feature could be enabled/disabled by user from WebUI.
The intent of this benchmark is to investigate the capability of BACRouter. Because of low baudrate of MSTP, there is not a bottleneck on routing packet to/from MSTP network.
BACRouter support 10/100M Ethernet interface, so there will be a challenge to flood it. The testing machine is a Notebook with i7 2.8G 4 cores CPU and 1000M Ethernet card, directly connected to BACRouter with CAT5+ cable. The result is:
|Path||APDU size in byte||Max routing rate without packet drop|
|Routing rate in packet flooding|
|Packet flood rate
When BACRouter is flooded by small packets, the handling capability dramatically decreased, especially in BIP port.
On 2019-04-16, We made new benchmark on firmware version 2.18, with a new testing machine( i5 4 core CPU and 1000M Ethernet card). the result is:
|Path||APDU size in byte||Max routing rate without packet drop|
|Routing rate in packet flooding|
|Packet flood rate
The performance is improved much with new firmware.