Embedded Systems Design, 2nd Edition

Buffering and other data structures 349

memory usage for small and simple data. Variable size

buffers are a solution to this but require more complex

control to handle the length of the valid data. The buffer size

must still be large enough for the biggest message and thus

the problem of buffer size granularity may come back

again.

• The buffers must be accessible by both the driver and

requesting tasks. This may seem to be very obvious but if

the device driver is running in supervisor mode and the

requesting task is in the user mode, the memory manage-

ment unit or address decode hardware may prevent the

correct access. This problem can also occur with ...