mbedTLS + NUCLEO-F401RE + SIM800

Mbed TLS Platform specific questions
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13

Hi,

After you do a successful TLS handshake between the peers, you send \ recv application data between them. mbedtls_ssl_write() and a corresponding mbedtls_ssl_read() are the the public API that you call to send\recv data to\from the peer. Internally, they encrypt \ decrypt the data with the TLS session key, and call the callbacks you have set.

OK, it is perfectly clear, thanks.
I am afraid I hit the roadblock Paul warned me regarding ram usage. I am getting an error 0x7200 from mbedtls_ssl_handshake(&ssl).

Looking back at other users had similar issues and your response, I am stripping down the config.h per the mini-TLS 1.2 example and your article suggestion.

Another thing I noticed:

static int my_send(void *ctx, const unsigned char *buf, size_t len) {
    HAL_UART_Transmit(&huart6, buf, len, 0xffff);

    custom_print(len);
    return len;
}

static int my_recv(void *ctx, unsigned char *buf, size_t len) {
    UART6rxComple = false;   /* is true when UART IDLE interrupt */
    HAL_UART_Receive_DMA(&huart6, (uint8_t *) buf, len);
    while (!UART6rxComple) { /* HACKS */ }
    HAL_UART_DMAStop(&huart6);  /* no more data in UART, stop DMA */

    custom_print(len);
    return len;
}

During handshaking, I am printing len for both send and recv, and it is populated, something like 1kb (i think, i am currently trying to enable the debug feature with UART and i will retest) for sending and 5 bytes(!) for recv. I will try to increase the MCU-modem baudrate or maybe somehow give the modem some time to spit out data because I suspect that there is something asynchronously messing up the recv buffer contents. For anyone else’s reference, I am utilizing an IDLE line interrupt from the UART to catch end of data receive, with volatile bool UART6rxComple toggling inside the IRQ IDLE callback. I can confirm that this modem, even for plain HTTP GET requests somehow transmits in UART the received data in chunks, e.g. one server response triggers two IDLE line interrupts.
I will write back further results.

Have a nice week,
Dimitris

edit: Let me add that until now, about 50% of my time with wrong configurations both on my host PC and on STM32, were because cmake cashes something (idk what) causing a new configuration to not load after compilations, expect if I also edit the source file as well or if I clear the cache