Timing requirements

Since the minidriver code is polled during the startup and kernel-initialization phases of the boot process, you need to know the timing of your device in order to verify if the poll rate is fast enough. Most of the time in startup is spent copying the boot image from flash to RAM and the minidriver is polled during this time period.

The startup contains a global variable mdriver_max, which is the size of data (in bytes) that is copied from flash to RAM between calls of your minidriver. The default size is 16 KB. The appropriate data size should be based on the timing requirements of your device, processor speed, and the flash. The file that contains this variable is called mdriver_max.c and can be found in the startup library.

In order to change this value, there are two options:

• You can copy this file to your specific board directory and then the value. The mdriver_max.c file contains the following variable:

  unsigned mdriver_max = KILO(16);
  

• Modify the startup program to initialize this variable to a new value, possibly in the main() function for your particular startup. Since this is a global variable, you can initialize it to a new value in main() before the minidriver handler is added.