AN4683 datasheet(21/31 Pages) STMICROELECTRONICS

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AN4683

Demonstration package

characters that must match the name specified in the server certificate (Common Name or

others).

When using AT+S.TLSCERT and AT+S.TLSDOMAIN with f_ca, f_cert, f_key and f_domain,

the file information is stored to Flash memory: since Flash memory is non-volatile, any file

stored in Flash memory will remain intact even when switching off or resetting the module.

Thus, to remove file information from Flash you can use the command

AT+S.TLSCERT2=clean,<f_ca|f_cert|f_key|f_domain> to selectively remove a specific file,

or AT+S.TLSCERT2=clean,all to remove all files information from Flash.

Note: Loading files to Flash memory is always preferred! Alternatively, you can use

AT+S.TLSCERT=<ca/cert/key>,<size><CR><data> and

AT+S.TLSDOMAIN=domain,<server domain> to load files to RAM, but note that:

RAM is volatile and in this case the loaded file information is lost after switch off or

module reset

files stored in RAM have higher priority than those in Flash

file upload to RAM is deprecated in favor of Flash

AT+S.SOCKON=<hostname>,<port>,s[,ind] opens a secure socket to server hostname on

port. The hostname is the IP address of the server, the port must correspond to the one

specified in OpenSSL server options, and the s parameter specifies a request for secure

socket. The parameter ind is optional and provides the indication (WIND:55, see below) that

some data has been received: if enabled, it is strongly suggested to immediately empty the

buffer when pending data is received (see SOCKQ and SOCKR commands below).

When the TLS handshake is successful, the AT+S.SOCKON gives back the sock id: only

then is it possible to write data to and read from the secure socket using AT+S.SOCKW,

AT+S.SOCKQ and AT+S.SOCKR.

If the parameter ind was enabled in SOCKON, asynchronous indications of pending data

from the secure socket may arrive at any time and have the format:

<CR><LF>+WIND:55:Pending Data:<sock id>:ENC<CR><LF>

When WIND:55 indications occur, the pending data is still encrypted, thus the length of

decrypted data is not known in advance. The SOCKQ can be used to get the actual length

of the data decrypted by TLS library and already waiting for reading.

Up to 4 consecutive WIND:55 messages (w/o SOCKR) are guaranteed. To prevent data

loss, it is suggested to empty the buffer by using the AT+S.SOCKR command and to avoid

exceeding 4 indications.

AT+S.SOCKW=<sock id>,<len>

AT+S.SOCKQ=<sock id>

AT+S.SOCKR=<sock id>,<len>

Note:

when using a secure socket, the module can handle data packets up to 3 KB. This means

that the len parameter in AT+S.SOCKW and AT+S.SOCKR can be up to 3072 bytes.

Detailed description of AT commands is contained in (see [2] in References).

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