Cortex-A8 Technical Reference Manual - ARM Information Center

End-of-test datalog retrieval
Design for Test
Figure 11-10 shows an example of retrieval of the first failure datalog and the pass/fail status for
every array. This is typically run at the end of testing. You can use bitmap test mode on the
failing arrays.
Be careful not to miss a subsequent failure that might occur near the end of the testing sequence.
For example, if a failure occurs on the last RAM access of the test sequence, then the complete
flag asserts only three at-speed cycles after the fail flag asserts. If the fail flag signal goes
through more external delay than the complete flag, the complete flag might be visible
externally before the fail flag. Before classifying a test as passing, give adequate time after
recognizing the complete flag to ensure that the fail flag does not assert.
CLK
ARESETn
MBISTMODE
MBISTSHIFT
MBISTDSHIFT
MBISTDATAIN
MBISTRUN
MBISTRESULT[2:0]
Bitmap datalog retrieval
b110 bxxx
xx,dlog[lsb] xx,dlog[msb-1] xx,dlog[msb]
Figure 11-10 Timing of MBIST end-of-test datalog retrieval
Figure 11-11 shows an example of the start of a failure datalog retrieval during bitmap mode.
The fail flag remains asserted and no more MBIST testing occurs until the MBISTDSHIFT
signal is asserted, that initiates the serial shift-out of the bitmap datalog. This provides time to
switch from fast to slow clocking required for shifting.
PLL glitchless switch between
fast and slow clocking occurs here
CLK
MBISTRESULT[1] (fail flag)
MBISTDSHIFT
MBISTRESULT[0] (data log shift out)
MBISTRUN
Figure 11-11 Timing of MBIST start of bitmap datalog retrieval
Figure 11-12 on page 11-18 shows an example of the end of a failure datalog retrieval during
the execution of a failure bitmap. When all of the bits are shifted out, the PLL switches back to
fast clocking and negates the MBISTDSHIFT signal. This causes the MBIST controller to
resume testing.
ARM DDI 0344K Copyright © 2006-2010 ARM Limited. All rights reserved. 11-17
ID060510 Non-Confidential
D[lsb]