libp7/PORTING.md

# Porting libp7 to a new platform
Basically, the two things you will have to do to port libp7 to a new platform
is making macros for non-standard but required functionnalities from your
platform's libc, such as endianness correcting or sleeping, in the internal
headers located in `include/libp7/internals/`, and make a custom stream adapted
for your platform and prototype it.

libp7 streams are the libp7 abstraction between it and the calculator device.
You can check out the current streams in `src/stream/`. Currently supported
streams are libc FILEs, Unix-like streams (with file descriptors), Microsoft
Windows's libc streams (`HANDLE`s) and libusb streams (which can be disabled
by passing `--no-libusb` to the configure script). Each stream must implement
a function to connect to the device using `p7_sinit`, and functions to read
and write, and eventually one to set communication settings from cross-platform
values defined by libp7. You should really check out `p7_sinit`'s manpage.

You should as well make up a constant like `P7_DISABLED_<your type of stream>`
(e.g. `P7_DISABLED_LIBUSB`, `P7_DISABLED_STREAMS`, `P7_DISABLED_WINDOWS`),
and define it in `libp7/stream.h` aside with the prototypes of your functions.

Once this is done, you will want to hook your stream to one of the libp7
standard initialization functions: `p7_init` or `p7_cominit`. In order to do
this, you should add it your functions to the content of at least one of these
two functions. Platform-specific things are preferred in your stream's source
file.