Emulation Timing Calculations
15-6
15.6 Emulation Timing Calculations
The following examples help you calculate emulation timings in your system.
For actual target timing parameters, see the appropriate device data sheets.
Assumptions:
t
su(TTMS)
Target TMS/TDI setup to TCK high
10 ns
t
d(TTDO)
Target TDO delay from TCK low
15 ns
t
d(bufmax)
Target buffer delay, maximum
10 ns
t
d(bufmin)
Target buffer delay, minimum
1 ns
t
(bufskew)
Target buffer skew between two devices
in the same package:
[t
d(bufmax)
– t
d(bufmin)
]
×
0.15
1.35 ns
t
(TCKfactor)
Assume a 40/60 duty cycle clock
0.4
(40%)
Given in Table 15–2 ( on page 15-5):
t
d(TMSmax)
Emulator TMS/TDI delay from TCK_RET
low, maximum
20 ns
t
su(TDOmin)
TDO setup time to emulator TCK_RET
high, minimum
3 ns
There are two key timing paths to consider in the emulation design:
-
The TCK_RET-to-TMS/TDI path, called t
pd(TCK_RET–TMS/TDI)
, and
-
The TCK_RET-to-TDO path, called t
pd(TCK_RET–TDO)
.
Of the following two cases, the worst-case path delay is calculated to deter-
mine the maximum system test clock frequency.
Case 1:
Single processor, direct connection, TMS/TDI timed from TCK_RET low.
t
pd
ǒ
TCK_RET–TMS
ń
TDI
Ǔ
+
ƪ
t
d
ǒ
TMSmax
Ǔ
)
t
su
ǒ
TTMS
Ǔ
ƫ
t
ǒ
TCKfactor
Ǔ
+
[20ns
)
10ns]
0.4
+
75ns (13.3 MHz)
t
pd
ǒ
TCK_RET–TDO
Ǔ
+
ƪ
t
d
ǒ
TTDO
Ǔ
)
t
su
ǒ
TDOmin
Ǔ
ƫ
t
ǒ
TCKfactor
Ǔ
+
[15ns
)
3ns]
0.4
+
45ns (22.2 MHz)
In this case, the TCK_RET-to-TMS/TDI path is the limiting factor.