Not sure how to resolve declared, (newb questions)

Hello, I am in the process of switching my 3d printer to marlin, after getting all my settings punched in , I verified and got this:

exit status 1
'rx_buffer' was not declared in this scope

How should I change this. I am using Marlin for source code and I am sure somebody out there understands this... :frowning:

Here is the bad code:

CRITICAL_SECTION_START;
(const ring_buffer_pos_t t = rx_buffer.tail) ;
if (rx_buffer.head == t) ;
v = -1;
else {
v = rx_buffer.buffer[t];
rx_buffer.tail = (ring_buffer_pos_t)(t + 1) & (RX_BUFFER_SIZE - 1);

Where is the rest of the bad code, and its code tags?

(deleted)

DMC3D:
Hello, I am in the process of switching my 3d printer to marlin, after getting all my settings punched in , I verified and got this:

There are thousands (maybe 10s of thousands) of lines of code in Marlin. You need to ask for advice on a Forum that is dedicated to Marlin.

...R