user-1: Can I use the arduino for an application with a frequency of 4 MHz?
I need to create a clk with this frequency and send and receive data on the rising and falling edges. and it is not a normal SPI interface I have my own conditions so I need to do it manually.
If it is not suitable, is it technically possible?

user7508: Most Arduinos are based on AVR chips clocked at 16 MHz. On those,
you can generate a 4 MHz clock using hardware timers. Bit-banging
data at this speed would be difficult though. It may be possible,
using unrolled loops and hand-crafted assembly... or not, depending on
the specifics of your application. Even if possible, it would be a nice
challenge for an assembly programmer.
The Arduino Due is based on an ARM chip clocked at 84 MHz. This
gives you more leeway to bit-bang at 4 MHz. But even on the Due you
would certainly need hand-crafted assembly.

-1: <p>Can I use the arduino for an application with a frequency of 4 MHz?</p>

<p>I need to create a clk with this frequency and send and receive data on the rising and falling edges. and it is not a normal SPI interface I have my own conditions so I need to do it manually.</p>

<p>If it is not suitable, is it technically possible?</p>
 7508: <p>Most Arduinos are based on AVR chips clocked at 16&nbsp;MHz. On those,
you <em>can</em> generate a 4&nbsp;MHz clock using hardware timers. Bit-banging
data at this speed would be difficult though. It <em>may</em> be possible,
using unrolled loops and hand-crafted assembly... or not, depending on
the specifics of your application. Even if possible, it would be a nice
challenge for an assembly programmer.</p>

<p>The Arduino Due is based on an ARM chip clocked at 84&nbsp;MHz. This
gives you more leeway to bit-bang at 4&nbsp;MHz. But even on the Due you
would certainly need hand-crafted assembly.</p>
