STM32F107VC/Bit-banding

Problem

WHen writing to memory addresses that are shared with multiple processes/tasks - the normal Read-Modify-Write solution can cause problems if another task i scheduled to run before the Read-Modify-Write cycle is finished and the new task makes its own Read-Modify-Write on the same shared address.

This problem could occur in the configuration Registers of Peripheral - fx. Timers, Interrupt Controllers.

Example

The Timer Enable Register (TER) at address 0x4001 is used to enable Timer 1 and Timer 2.

Timer enable Register (TER).

bit 7	bit 6	bit 5	bit 4	bit 3	bit 2	bit 1	bit 0
X	X	X	X	X	1 = Enable Timer 2 0 = Disable Timer 2	1 = Enable Timer 1 0 = Disable Timer 1	X

Timer 1 is used by Task A and Timer 2 is used by Task B.

Example of problem.

Action	TER at 0x4001
Task A Reads TER !!