Trouble with i2c/C interop with V

[wbehrens-on-gh]

here's my code:

module i2c

import os

#include <sys/ioctl.h>

fn C.ioctl(int, u32, voidptr) int

pub const(
	// I2C ioctl commands
	ioctl_cmds = {
		'rdwr': 	byte(0x0707)
		'slave':        byte(0x0703)
		'slave_force':  byte(0x0706)
		// I2C_TIMEOUT	0x0702
		// I2C_RETRIES	0x0701
		// I2C_TENBIT	0x0704
		// I2C_FUNCS	0x0705
		// I2C_PEC	0x0708
		// I2C_SMBUS	0x0720
	}
)

pub struct Device {
	name string
	address byte
mut:
	bus os.File
	is_connected bool
}

pub fn new_device(name string, address byte, path string) ?Device {
	// Fill device parameters
	mut self := Device {
		name: name
		bus: os.open_file(path, 'rbwb') or { // Read and write file in binary mode
			return error('Unable to open I2C bus!')
		}
		address: address
	}

	// Set I2C slave address
	if C.ioctl(self.bus.fd, ioctl_cmds['slave'], voidptr(self.address)) < 0 {
		self.bus.close()
		return error('Unable to add ${self.name} as I2C slave!')
	}

	// Update connection status
	self.is_connected = true
	return self
}

pub fn (mut self Device) read(length int) ?[]byte {
	rbytes := self.bus.read_bytes(length)
	if rbytes.len <= 0 {
		return error('Unable to read from I2C bus!')
	}
	return rbytes
}

pub fn (mut self Device) write(data []byte) ?int {
	return self.bus.write(data) or {
		return error('Unable to write data to I2C!')
	}
}

pub fn (mut self Device) disconnect() {
	if !self.is_connected {
		return
	}
	self.bus.close()
	self.is_connected = false
}

I'm trying to write a basic i2c library using mostly V but I'm struggling as the C.ioctl() function keeps failing.

V panic: Unable to add cntl as I2C slave!
v hash: f2e0ab5
[Vweb] Running app on http://localhost:80/
/home/will/Code/RCBot/modules/main/main.v:58:           |       0x4b9f6a | ./rcbot(main__main+0x5e7) 
/home/will/.local/v/vlib/vweb/vweb.v:50:                |       0x4c774b | ./rcbot(main+0x29) 
                                                        | 0x7fe4558fafd0 | /lib/x86_64-linux-gnu/libc.so.6(+0x29fd0) 
                                                        | 0x7fe4558fb07d | /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0x7d) 
                                                        |       0x41d3d5 | ./rcbot(_start+0x25) 

I was wondering if anyone could help point me in the right direction because I've been stumped by this for the past 3 days(I also tried it on an rpi 0 to the same result)

[ylluminate]

This seems like https://github.com/vlang/v/issues would be a better fit. Also you might find faster interaction via Discord (https://discord.gg/vlang) #embedded.

[dumblob]

Let V generate the C source code and read the source code to find out if it does exactly what you'd write in C.

You also might have a look at the ioctl() function use in V sources:

master % 0$ grep -Eir ioctl .
./thirdparty/libgc/gc.c:if (ioctl(fd,PIOCNMAP,&needed_sz)< 0){
./thirdparty/libgc/gc.c:ABORT_ARG2("/proc PIOCNMAP ioctl failed",
./thirdparty/libgc/gc.c:if (ioctl(fd,PIOCMAP,addr_map)< 0){
./thirdparty/libgc/gc.c:ABORT_ARG3("/proc PIOCMAP ioctl failed",
./thirdparty/libgc/gc.c:obj=ioctl(fd,PIOCOPENM,&arg);
./vc/v.c:#if __has_include(<sys/ioctl.h>)
./vc/v.c:#include <sys/ioctl.h>
./vc/v.c:#error VERROR_MESSAGE Header file <sys/ioctl.h>, needed for module `term` was not found. Please install the corresponding development headers.
./vc/v.c:#include <sys/ioctl.h>
./vc/v.c:       ioctl(1, ((u64)(TIOCGWINSZ)), &w);
./vlib/builtin/linux_bare/old/linuxsys_bare.v:16  sys_ioctl unsigned int fd unsigned int cmd  unsigned long arg
./vlib/term/term_nix.c.v:#include <sys/ioctl.h>
./vlib/term/term_nix.c.v:fn C.ioctl(fd int, request u64, arg voidptr) int
./vlib/term/term_nix.c.v:       unsafe { C.ioctl(1, u64(C.TIOCGWINSZ), &w) }
./vlib/term/ui/termios_nix.c.v:#include <sys/ioctl.h>
./vlib/term/ui/termios_nix.c.v:fn C.ioctl(fd int, request u64, arg voidptr) int
./vlib/term/ui/termios_nix.c.v: C.ioctl(0, C.TIOCGWINSZ, &winsz)
./vlib/net/tcp.v:       // we shouldnt be using ioctlsocket in the 21st century
./vlib/net/tcp.v:                       socket_error(C.ioctlsocket(handle, fionbio, &t)) ?
./vlib/net/tcp.v:                       socket_error(C.ioctlsocket(sockfd, fionbio, &t)) ?
./vlib/net/tcp_read_line.v:             socket_error(C.ioctlsocket(con.sock.handle, fionbio, &t)) ?
./vlib/net/aasocket.c.v:fn C.ioctlsocket(s int, cmd int, argp &u32) int
./vlib/net/udp.v:                       socket_error(C.ioctlsocket(sockfd, fionbio, &t)) ?
./vlib/readline/readline_linux.c.v:#include <sys/ioctl.h>
./vlib/readline/readline_linux.c.v:     cols := if unsafe { C.ioctl(1, C.TIOCGWINSZ, &ws) } == -1 { 80 } else { int(ws.ws_col) }