Universal serial connector for Beremiz proposal

[nucleron]

Architecture

The connector consists of two parts:

• A dynamic library with standartized API/ABI;
• Beremiz connector which loads a dynamic lib and use it as a transport to PLC.

Dynamic lib

Dynamic lib gives us a serial transport with standart API/ABI. Libs internals may use sockets/pipes/files/devices/etc. It can implement any transport that PLC vendor like, the only requirement, is standart API/ABI. The proposed API/ABI is:

int handle_open (void ** handle, char * uri, uint32_t uri_len); //Returns zero on successfull connection creation
int handle_close (void ** handle); //Returns zero on success
int handle_read  (void ** handle, void *buf, size_t nbyte); //Returns numer of bytes red
int handle_write (void ** handle, void *buf, size_t nbyte); //Returns number of bytes written

Where:

• handle - an opaque pointer for transport control entity.
• uri - a pointer to sockets/pipes/files/devices/etc name.
• uri_len - URI length (yes we will try address possible buffer overflow).
• buf - a pointer to data buffer used for communication.
• nbyte - a number of byte to transmit/receive.

Beremiz connector

The connector itself implements serial connection protocol, we propose LPCManager or YAPLC/IDE protocols as a base.

It also should have standart Beremiz side connector API, if someone adds data buffering to connector it would be very cool.

We propose the following URI format for connector:

UNIDBG://Path_to_dynamic_lib//Transport_uri

Where:

• Path_to_dynamic_lib - A path to dynamic lib file (I beleive it should be relative to some base dir).
• Transport_uri - a string that will be passed to handle_open as uri. So PLC vendors can implement any transport layer they like and they can use the same connector for different transports.

Issues

• 32/64 bit: 32bit python wants 32bit dll, 64bit python wants 64bit lib at least on Windowr(R).
• Boot protocol: different vendors use different boot protocols (e.g. we use STMicros-bootloader for program boot) and different file types to boot their PLCs, we must design some common way to handle these differences.