hcContLen in the ELS-31V and the PLS62W and more than 1500 byte writes | Telit Cinterion IoT Developer Community
March 7, 2020 - 8:40pm, 1182 views
I am trying to send a ~50K picture .jpg and have run into the 1,500 byte limit per SISW operation. According to the AT commands description for SISS where hcContLen is defined, it can be defined up to 2^31-1 as the Http post size. When I assign a value of, for example, 99999, it will only display "9999", limiting it to 4 digits. So my questions are as follows. Is the value that entered correct or is hccontlen limited to 9999?
Actual output after doing:
^SISS: 0,"hcContent"," "
Second Question: Once I set hccontlen to a value greater than 1500 (for example: 99999), do I execute multiple at^sisw=0,1500,1 to write more than 1500 bytes? I read something about "chunk encoding" on the http layer, so I am assuming that I can do multiple writes until I reach my hccontlen length of 99999.
Thank you, kinda stuck here!
Tracer Technology Systems, Inc.
I don't have experience with this particular module but usually it works in this way:
- If hcContent is set to 0, the data stores under hcContent parameter (0-255 bytes) is sent without a need to use SISW command.
- If hcContent value is greater than 0, it does not need to reflect the real amount of data to be sent. Then AT^SISW command is needed to send the date and it can be called many *****. In the end you SISW with end of data flag ***** to be sent (for example AT^SISW=1,0,1). There should be an example in the AT commands specification document - please see 'Examples of how to Configure and Use Internet Service Profiles'.
Thank you for your input. We have a couple products in production that use the modules w/o issue but we have been carteful to limit our payload size to less than 1500 bytes. The need on a new product is to send much more than 1500 bytes therefore we run into the limiting factor of these modules. There is some reference about having the hccontlen parameter set for the http transfer file size, and then sending multiple 1500 byte sisw events to transfer the larger amount of data, but there is no mention if this is possible. I wrote the software for the smaller transfers so very familure with the modules performance...just less that 1500 bytes.
1500 bytes is the limit for a single SISW write operation but it has nothing to do with the oveall data size that we send during a connection or in HTTP POST operation. Please try to do a test.