60.6.4.3 Granting System Access After Going Out of Imprinting Conditions

As described in Conditions Enabling or Disabling the Non-Imprinting Process, when the non-imprinting enable condition becomes false, the process is stopped in a few ICLK clock cycles (if it was running).

During this time, the processor cannot access the memory and must wait for the automatic end of process. Due to the frequency difference between the processor clock and the ICLK clock, adding thousands of Wait states on the system bus (which would lock the application for a long time) would be inappropriate. It was decided instead to add a register in the SECUMOD user interface, SECUMOD_RAMRDY, which returns the availability status of the memory.

The following formula gives the maximum number of processor cycles to wait before RAMRDY is set.

CPU cycles ≤ 3 × f_CPU/f_ICLK