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The CWL makes no assumptions about the filesystem on the implementor's platform, or even if a traditional file system exists. For example, many deeply embedded platforms simply have interfaces that read and write to a non-volatile memory that is partitioned statically. Other platforms, such as Linux, will have full desktop compatible, wear leveling flash file systems. The CWL can easily work with either setup. Implementors should consider the file names used in OKMs to be logical and not necessarily have or demand a direct manifestation as a "real" file.

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cwm_buffering cwm_buffering

CWM Buffering

File transfers may need to move large quantities of data. Many embedded systems will have limited amounts of high-speed RAM buffers, and there can be significant latency and throughput bottlenecks when writing data out to a non-volatile memory. So how can a small embedded system handle the onslaught of file data sent to it from the cloud computers with 10 Gigabit network connections?

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By decoupling file transfer between an OKE system from the OKC, the CWM allows an OKE system to easily manage having large files written to it and write large files to the OKC.

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oke_inbound_ft_throttling oke_inbound_ft_throttling

OKE Inbound File Transfer Throttling

As an OKE receives inbound file write fragments it may easily throttle the CWM from sending the next fragment for up to 4 seconds without triggering serial communication layer timeouts. Implementors should add code to the CWPortIsAppBusy() function that will return true when the application is not ready to handle the next file fragment, and false otherwise. The CWPortIsAppBusy() function must not return true for more than 4 consecutive seconds otherwise serial communication timeouts may occur. Serial communication is always gracefully recovered after a timeout but nevertheless should be avoided.

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Should the non-volatile memory need to be erased before a write is initiated then implementors should erase the smallest partition necessary to complete the next write to minimize the erase time. For example, it is better to make 16 4KB erase requests that each take 250ms than a single 64KB erase request that takes 4 seconds.

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aborting aborting

Aborting an OKE Inbound File Transfer

An OKE may abort an inbound file transfer at any time by returning false when CWPortExeFileWrite() is invoked by the library. For example, an OKE may abort or prevent a file transfer if the user enters a technician diagnostic mode. Generally, implementors should minimize or eliminate modes during which file transfers are not permitted.

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large_files large_files

Transferring Large Files

Files larger than the CWM ISFQ can be transferred from the OKC to an OKE. This is possible by the OKC actively monitoring the progress of the file transfer to ensure that it does not overrun the CWM ISFQ. Using this technique files up to 2GB can be transferred.

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faster_baud faster_baud

Faster Baud Rate Negotiation

When CW_PORT_DYNAMIC_BAUD_ENABLED is set to 1 in cwport.h the CWL will automatically attempt to negotiate the baud rate defined by CW_PORT_BAUD_RATE_FAST with the CWM. The OKE starts at default baud rate defined by CW_PORT_BAUD_RATE_DEFAULT and the library will try to increase the rate to the desired speed. If the CWM supports running at the higher speed, then both the OKE and CWM will switch. If any communication failures occur or the baud rates get out of sync both the OKE and CWM will drop back to the default baud rate and resynchronize. The OKE will request the baud rate to increase again. Typically, this option will only be used by OKEs using the TTL or 232 bus and that regularly transfer large files >10MB. Other OKEs can simply ignore this option and run at the default baud rate. The allowed values for faster baud rate are 230400, 250000, 500000, and 1000000.

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fastest_interface fastest_interface

Fastest Interface

The USB interface can support the highest transfer speeds. Although the 232 and USB transfers rates are similar with the current WiFi CWM hardware, in the future newer CWM hardware will allow the USB interface to go much faster than 1000000 baud.

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throughput throughput

File Transfer Throughput

The amount of time it takes to transfer a file is a function of many variables including file size, processing latencies, and link bandwidths. The following table shows the estimated throughput between the MiWi and WiFi CWM versus the OKE connection type:

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2. A file version to differentiate between different file encodings. This ensures files with incompatible encodings are safely ignored by the OKE.

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file_transfer_status file_transfer_status

File Transfer Status

When the OKC is writing a file, an OKE system will report on the status of the write operation. This allows the OKC to determine if the file transfer is ongoing, stalled, or completed. If the file transfer appears stalled, for example only half the file was downloaded due to a network connectivity problem. Then the OKC can restart the file transfer from where it left off without starting from the beginning. This can be very helpful when attempting to transfer large files in challenging network conditions. The CWL automatically sends File Transfer Status updates to the OKC.

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file_status file_status

File Status

Independent of reporting the current status of a file being written to the OKE, the names of important individual files maintained by the OKE are also reported automatically by the CWL.

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Some examples of files that might make sense to report are the name of recipe configurations, or the name of diagnostic logs. It is not necessary to list the names of firmware files since they are enumerated in the version data. The idea is to enable the equipment to be effectively managed by the OKC. Implementors should think about the capabilities of the product and the use cases for its utilization. Based on this knowledge, provide file information to the OKC that can enhance it manageability.

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firmware firmware

Firmware

Many systems that implement file transfer will also implement in-system firmware updates. The OKC will transfer firmware images to an OKE system via a file write. An OKE system will be able to write the new firmware image to secondary storage. If the file transfer is successfully and the firmware passes platform specific integrity checks then it should be automatically installed.

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writing_okc_to_oke writing_okc_to_oke

Writing from the OKC to an OKE System

bool CWPortGetInboundFileWriteBuf(uint8_t** buf, uint16_t* bufSize);

bool CWPortExeFileWrite(int8_t* fileStr, uint32_t offset, uint8_t* data, uint16_t dataLen, int32_t fileSize) ;

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The CWPortExeFileWrite()  must return true if it successfully processed the file fragment. If an unexpected error occurs, then the function must return false.

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throttling throttling

Throttling File Fragments

As previously discussed, the CWM buffers all file fragments from the OKC. The OKE can determine the pace at which the file fragments are received in case its local non-volatile memory cannot be written to fast enough. This section describes two strategies for the OKE to implement throttling.

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Implementors may also consider lazy blocking. For example, after writing data to a non-volatile memory the memory usually goes into a busy state for a period during which it cannot accept new writes. Instead of writing and immediately blocking waiting for the write to complete the CWPortExeFileWrite() function should return without blocking. The next time the CWPortExeFileWrite()  function is called it can block conditionally only if the write operation is still in progress. Deferring the memory busy check can increase file throughput considerably.

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pseudocode_example pseudocode_example

Pseudocode Example

This example code is from the Windows port of the CWL.

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Bool CWPortGetInboundFileWriteBuf (uint8_t** buf, uint16_t *bufSize) {

    static uint8_t ftBuf[CWMSGCMD_FT_MAX_SIZE];

    CW_REQUIRE(buf != NULL);

    CW_REQUIRE(bufSize != NULL);

    *buf = ftBuf;

    *bufSize = sizeof(ftBuf);

    CW_ENSURE(*buf != NULL);

    CW_ENSURE(*bufSize >= CWMSGCMD_FT_MAX_SIZE);

    return true;

}

bool CWPortExeFileWrite (int8_t* fileStr, uint32_t offset, uint8_t* data, uint16_t dataLen) {

CW_REQUIRE(fileStr != NULL);

CW_REQUIRE(data != NULL);

    CW_REQUIRE(dataLen <= CWMSGCMD_FT_MAX_SIZE);

    if (offset == 0) {

        if (fpWrite != NULL) fclose(fpWrite); /* Close open files */

        CW_ASSERT((fpWrite = _fsopen(fileStr, "wb+", _SH_DENYNO)) != NULL);

    }

    CW_ASSERT(fwrite(data, 1, dataLen, fpWrite) == dataLen);

    if ((dataLen < CWMSGCMD_FT_MAX_SIZE) && (fpWrite != NULL))

    { fclose(fpWrite);}

    return true;

}

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common_problems common_problems

Common Problems

1. OKE implementation expects a hardcoded file name and file uploaded to OKC doesn’t match:
   It’s commonly seen that developers hard code an expected file name for certain file types, e.g. firmware.bin, menu.json. If someone subsequently uploads a file to the OKC with a different name (e.g. firmwareV1-2-3.bin), the file will be downloaded to the OKE (and indeed the status shown in Open Kitchen will be ‘downloaded’), but it isn’t loaded into the system because of the name mismatch. We recommend avoiding this approach and to instead encode identifiable information in the file header. If not avoidable, then ensure the file uploaded to the OKC is correctly named

2. Old CWM firmware and/or CWL version: In CWM1 firmware earlier than PIC154/SPH145 and ConnectWare Library versions < 1.0.15, there was a bug in the fragmentation layer that caused messages of certain lengths to be dropped. This can cause a multitude of issues including download rewinds due to dropped fragments (ultimately ended in an aborted download), and files that do ‘successfully' download to the CWM but aren’t loaded into the OKE. If you encounter such issues, please ensure your CWM firmware and CWL versions are up to date.

3. File name + extension longer than 16 characters: the OKC now prevents this from happening, but it may still be possible to do with the simulators. The CWL has a 16 character limit on the file name including the extension. If this limit is exceeded, the CWM will download the fragments from the OKC but just throw them away. Please ensure file names are <= 16 characters including extension.

4. File Name + Version + Account ID not unique combination: Currently, there is a unique index in Open Kitchen Database that requires a combination of File Name - Version - Account ID to be unique even the uploaded file has been deleted. If Version does not have value entered by user, it will have timestamp value. However, user can enter Version for it to be used to match with equipment data for file transfer status. If this is the case, it may cause violation of unique File Name + Version + Account ID combo key. In this scenario, if a firmware file needs to be uploaded from the same Account, it needs to have unique File Name and Version (if input by user) every time it is uploaded even after it is deleted from Open Kitchen.