C programming examples?

Thanks. I'm not sure that there is need to use WiringPi here -- isn't the low-level voltage-wiggling stuff done by the kernel's i2c module? If I understand correctly, it should "just" be necessary to take the Arduino code and replace the calls to Wire with ordinary read()/write() calls, once you've set the interface up.

Is that right?

I note that the Arduino code has functions for operating the PicoBorg Reverse using a (shaft?) encoder. But the board itself does not seem to have ny connections for a shaft encoder. Am I missing the point, or is additional hardware needed for this mode of operation?

Finally -- what is needed to test whether I can get basic i2c operation working? I mean, will the board actually operate with no motors connected, to the extent that at least I can query status using i2c? Does the battery connection to the board just power the motors, or does it power the logic as well?

It would be nice to get some clarity on the WiringPi issue. I've seen i2c programming examples on various websites that use this library, and others that don't. I looked at the WiringPi source, and I note that it does require that kernel i2c support is enabled, so it isn't doing its own low-level logic control. It seems to do all its work using ioctl() calls on /dev/i2c-xxx, rather than plain read()/write() calls as the PiBorg guys advised.

Is it possible that the kernel's support for i2c has changed, such that it is now possible to control the bus using plain read/write operations? I can see how using WiringPi would be advantageous if the alternative were a string of incomprehensible ioctl() calls.

Using an additional library doesn't bother me, but I rather suspect that most people who are using WiringPi for i2c stuff are doing so because it has a similar interface to the Arduino Wire library, which makes it easier to port code.

Thanks. Sure, it doesn't seem to be a big deal one way or the other. Just trying to make sense of the conflicting reports that Mr Google is taking me to.

Hiya

Only got my reverse this morning, so I haven't done much with it. However, I'm able to turn the on-board LED on and off in C code. Basically:

int f = open ("/dev/i2c-1", O_RDWR);
ioctl(f, I2C_SLAVE, 0x44); // Select the Reverse on the bus
unit8_t buff[1];
buff[0] = 1;  // Code to set LED
buff[1] = 1; // 1 = on
write (f, buff, 2);
close (f);

There may be some subtleties I'm missing, but that seems to work fine for me so far.

To be honest, the I2C commands to control the motors don't look any more complicated than this -- it's just a matter of figuring out which bytes to send, by decoding the Arduino example.

When I get the motors working (or at least my simulation of the motors, since I haven't ordered them yet), I'll try to post some proper code on my website.

Best wishes
Kevin

Hi

For the record, it really is as simple as I thought to control the motors in C. I was going to post a code example, but it's so easy that it's hardly worth it :) It's just a case of calling ioctl() as in my previous post, writing one or more bytes to the i2c device and then reading one or more bytes if the command returns data. The devil might be in the details, I guess, but this is working fine for me so far.

The only slightly tricky part is reverse-engineering the actual send and receive bytes from the Arduino example. For the record, I have attached a brief summary of the i2c protocol -- at least those bits of it I have tested.

Best wishes
Kevin

=================

Each command requires the transmission of one or two bytes; responses
are zero to two bytes.

Note "motor1" here refers the connections so labelled on this page:
https://www.piborg.org/picoborgrev/specs. Compared with PiBorg's Arduino
code, motor1=motorB, motor2=motorA. Go figure.

Get ID
Send 0x99, Receive 0x99,0x15 if correct board

Set LED status
Send 0x01,N where N=1 or 0

Get LED status
Send 0x02, receive 0x02,N where N=1 or 0

Set motor1 fwd
Send 0x6,N where N 0-255

Set motor1 rev
Send 0x7,N where N 0-255

Set motor2 fwd
Send 0x3,N where N 0-255

Set motor2 rev
Send 0x4,N where N 0-255

Get motor1 speed and direction
Send 0x08, receive 0x08,D,S where D=1 is fwd, D=2 is reverse, S is speed 0-255

Get motor2 speed and direction
Send 0x05, receive 0x05,D,S where D=1 is fwd, D=2 is reverse, S is speed 0-255

Stop all
Send 0x09