Another very low access method with the devmem utility

Hi !

We've started testting Linux Software development with PEEK and POKE commands.

3.1 - Very Low Level access with Peek and Poke

And then we moved to the mmap system call.

3.2 - Easy Custom IP access with application development based on mmap

In this post we've seen the mmap system call is based on the /dev/mem system virtual file use.



Well, I've just discovered that the /dev/mem is also directly available from the command line using a utility application provided by BusyBox which is called devmem !

This provides us a second very low level access method with the PEEK and POKE commands.


So let's see that we can do the same things as the PEEK and POKE commands !

Stage 1

Some information about the devmem utility use.

Stage 3

Now, to force the output led to ON, we only have to do the same steps as in the LED_TEST_IP_SetLedOn function of our driver.

Remember that our custom IP LED_TEST_IP is located at the physical offset 0x43C0_0000.

Which gives.

And there you go !

The led is ON on the MiniZed board.

Stage 4

Now, to force the output led to OFF, we only have to do the same steps as in the LED_TEST_IP_SetLedOff function of our driver.

Which gives.

And there you go !

The led is OFF on the MiniZed board.

Stage 5

Now, to force the output led to BLINK, we only have to do the same steps as in the LED_TEST_IP_SetLedBlink function of our driver.

Which gives.

And there you go !

The led blinks on the MiniZed board.

Post Conclusion

Now we have :

- Used the devmem utility application from the command line to control the behavior of our custom IP.

Like the PEEK and POKE commands, this is another methode to avoid writting a single line of software !

It can be a usefull tool.