raw i2c I/O

[csboling]

For debugging and developing other I2C devices, or general experimentation, it would be useful to expose a Lua API for handling raw bytes and arbitrary addresses. Seems fine if there's an 8 byte limit or whatever.

[trentgill]

This is not difficult. Just requires duplicating a bunch of a hooks from Lua. The main issue is in ii_leader_enqueue https://github.com/monome/crow/blob/main/lib/ii.c#L121 where commands are looked up from the descriptors (ii_find_command and type_size), so those values will need to be passed through from lib/lualink.c. We do this normally so sending the wrong count of arguments fills in the zeroes, and so Lua floats get converted to the appropriate bit-representation per command - ie. so the user doesn't have to know if it's 8bit/16bit, MSB first whatever.

The easiest solution would be to force the user the send everything as a sequence of bytes (so they will have to do the bitshifting in lua if it's a 16bit destination).

The current lua interface (https://github.com/monome/crow/blob/main/lua/ii.lua#L34) has ii.get and ii.set which are used by the autogenerated lua files. These functions just call into C, but they will fail if the address and/or commands are unknown by the ii-descriptor system. Rather than overload these functions, should we add ii.get_raw and ii.set_raw? These are potentially confusing with lua's internal use of rawset and rawget.

When it comes to doing an ii get, I don't know how this would work? The current implementation is:

function ii_LeadRx_handler( addr, cmd, _arg, data )
    local name, ix = ii.is.lookup(addr)
    local rx_event = { name   = ii[name].e[cmd]
                     , device = ix or 1
                     , arg    = _arg
                     }
    ii[name].event(rx_event, data)  -- WHAT DO WE CALL FOR A RAW ACCESS?
end

We could just piggyback on this function by checking if ii[name] is not nil, then acting as normal, or forwarding to ii.event_raw(e, value) if the device doesn't exist?

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So yeah. This is not difficult, just an afternoon of typing & testing if someone wants it.