armv7_pmnc_read
nb_cnt = (armv7_pmnc_read() >> ARMV7_PMNC_N_SHIFT) & ARMV7_PMNC_N_MASK;
armv7_pmnc_write(armv7_pmnc_read() | ARMV7_PMNC_E);
armv7_pmnc_write(armv7_pmnc_read() & ~ARMV7_PMNC_E);