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<div class="moz-cite-prefix">On 2/9/20 7:19 μ.μ., Martin Peach
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAN5xZ3Y_pP+c6=LsZBY0WKFdBhzefQtz3LctbC1t4ajXMotE_Q@mail.gmail.com">
<pre class="moz-quote-pre" wrap="">On Tue, Sep 1, 2020 at 1:19 PM Alexandros <a class="moz-txt-link-rfc2396E" href="mailto:adrcki@gmail.com"><adrcki@gmail.com></a> wrote:
</pre>
<blockquote type="cite">
<pre class="moz-quote-pre" wrap="">
The MAX_I2C_BUF_SIZE macro in pii2c.c is set to 64, but still when I try
to send 64 bytes to a slave Teensy, only 32 go through, the rest 32 are
all 0s. Raising this value to an even greater number, like 128 (which is
something I would like to implement), gives similar results. The same
behavior occurs whether I set the I2C address as an argument to the
object, or if I pass it through the "write" message.
I checked the code and couldn't find where this occurs. I added this:
`post("%d", x->x_xferbuf[i-1]);`
to line 348 to make sure the bytes are stored in the object's buffer,
and they do get stored properly. The only place I found they end up in
is a "write()" function, called in line 293, inside the pii2c_writer()
function. I guess this function is from one of the header files included
in the object, as I couldn't find it in the code.
Long story short, is it possible to send more than 32 bytes over I2C in
the Pi? I really like [pii2c], and since wiringPi is now deprecated, I'd
like to stick to this object.
</pre>
</blockquote>
<pre class="moz-quote-pre" wrap="">
It seems to be an issue with the kernel driver. Whoever wrote it got
it into thieir head that there was a 32-byte limit. I found this
discussion:
<a class="moz-txt-link-freetext" href="https://stackoverflow.com/questions/25982525/why-i2c-smbus-block-max-is-limited-to-32-bytes">https://stackoverflow.com/questions/25982525/why-i2c-smbus-block-max-is-limited-to-32-bytes</a>
The same thing happens in Arduino, but there you can edit Wire.h to
get bigger messages.
I guess it will be fixed eventually.
Meanwhile, do you really need to use I2C? SPI is much faster and has
no limit to the message size. I also made a [pispi] external...
I find in general it's easier to plug an arduino into the pi to do
realtime stuff.
Martin
</pre>
</blockquote>
<p>Plugging an Arduino straight into the Pi is surely an easier
solution, but what I'm trying to do is for a more complex setup.
There's already a Teensy connected to the Pi over serial and I
want to be able to control more micro-controllers without
definitely knowing the exact number of them. For such a case I2C
is probably the best solution as it uses the same 2 pins for any
number of connected devices on the same bus, whereas SPI needs at
least three pins for a one-direction communication, plus an
additional pin for each additional slave.</p>
<p>In the link you posted, in the answer there's this chunk of code:</p>
<p>```<code><span class="pln"><br>
i2c_write</span><span class="pun">(</span><span class="typ">int</span><span
class="pln"> file</span><span class="pun">,</span><span
class="pln"> </span><span class="typ">int</span><span
class="pln"> address</span><span class="pun">,</span><span
class="pln"> </span><span class="typ">int</span><span
class="pln"> subaddress</span><span class="pun">,</span><span
class="pln"> </span><span class="typ">int</span><span
class="pln"> size</span><span class="pun">,</span><span
class="pln"> </span><span class="kwd">char</span><span
class="pln"> </span><span class="pun">*</span><span
class="pln">data</span><span class="pun">)</span><span
class="pln"> </span><span class="pun">{</span><span
class="pln">
</span></code></p>
<pre class="lang-c prettyprint prettyprinted" style=""><code><span class="pln"> </span><span class="kwd">char</span><span class="pln"> buf</span><span class="pun">[</span><span class="pln">size </span><span class="pun">+</span><span class="pln"> </span><span class="lit">1</span><span class="pun">];</span><span class="pln"> </span><span class="com">// note: variable length array</span><span class="pln">
ioctl</span><span class="pun">(</span><span class="pln">file</span><span class="pun">,</span><span class="pln"> I2C_SLAVE</span><span class="pun">,</span><span class="pln"> address</span><span class="pun">);</span><span class="pln"> </span><span class="com">// real code would need to check for an error</span><span class="pln">
buf</span><span class="pun">[</span><span class="lit">0</span><span class="pun">]</span><span class="pln"> </span><span class="pun">=</span><span class="pln"> subaddress</span><span class="pun">;</span><span class="pln"> </span><span class="com">// need to send everything in one call to write</span><span class="pln">
memcpy</span><span class="pun">(</span><span class="pln">buf </span><span class="pun">+</span><span class="pln"> </span><span class="lit">1</span><span class="pun">,</span><span class="pln"> data</span><span class="pun">,</span><span class="pln"> size</span><span class="pun">);</span><span class="pln"> </span><span class="com">// so copy subaddress and data to a buffer </span><span class="pln">
write</span><span class="pun">(</span><span class="pln">file</span><span class="pun">,</span><span class="pln"> buf</span><span class="pun">,</span><span class="pln"> size </span><span class="pun">+</span><span class="pln"> </span><span class="lit">1</span><span class="pun">);</span><span class="pln">
</span><span class="pun">}
```
</span></code>and the OP says this worked, where in the OP he mentions he needs to
send 189 bytes. I don't really understand this bit of code, but I do see
these functions (ioctl() and write()) are used in your code as well. In
the worst case scenario I'll go with 32 bytes... I'll definitely check
your [pispi] object though, I really like your work for interfacing Pd
with peripherals!
<code><span class="pun"></span></code></pre>
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