question about util/uart.c

[mocasrhey]

I'm working on a school project using SIM7000E and i'm exploring the DAM.
I was going through uart.c code and my mind blocked on this piece of code, if someone could explain me(im fairly new around here), i would apreciate it very much.

Here is the code(in file uart.c, uart_init() function, Lines 61 to 64):
uart_context_t mctx = (uart_context_t)cfg->buf;
mctx->sendbuf = (char*)cfg->buf + sizeof(struct uart_context_s);
mctx->send_buf_len = cfg->buf_len - sizeof(struct uart_context_s);
mctx->is_off = false;

[Thalhammer]

Yeah sure.
In a DAM module you cant just use malloc to get memory, however, uart_init needs some memory to do buffering.
That's why you pass a buffer in the uart config which is used for housekeeping and buffering.
Line 60 cleans the buffer to a known state and makes sure there is no garbage inside.
Line 61 casts it into a uart_context_t (which is a typedef for uart_context_s*) to make accessing easier
Line 62 sets the sendbuf pointer inside the struct to the remaining space in the supplied buffer and
Line 63 sets the send_buf_len to the remaining length (i.e. the length of sendbuf).
Line 64 sets the internal power state to off (it is used for bookkeeping as some powersave funktions do not work when the uart is on).

If you use it in a school project please beware of a few things:

• If you experience any bugs in the apis (and I almost guarantee you will) feel free to create an issue.
• Emailing Qualcomm/Simcom is pointless but you can try of course try.
• If you need timing with steps less then ~10ms it wont work.
• See the other bugs already noted here (most importantly qapi_Timer_Sleep() does not work with other units than TICK #2 Inconsistent behaviour between gcc and armcc #3 and Memleak in Timer #4)

[mocasrhey]

thank you so much for the answer.
Yes i've taken a look to those issues already. Im actually trying to make a bridge, that basically consists in receiving mqtt packets and forward them through UART to another board.