Specifications

CHAPTER 6. REQUIREMENTS VERIFICATION 61
The second test series was performed measuring the time intervals for ACPI buttons.
Figure 6.3 shows the results of the passes for the ACPI button driver. At low system load, the
minimum of t
2
was t
min
= 1ms and the maximum was t
max
= 8ms. The average time interval
is t
avg
= 2.33ms. The corresponding values for t
2
at high system load are: t
min
= 2ms and
t
max
= 17ms. The average time interval is t
avg
= 6.51ms.
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49
0
2
4
6
8
10
12
14
16
18
Pass
High Load
Low Load
/ ms
2
t
Figure 6.3: ACPI Button Event Time Interval
At last, the time intervals for events reported by the Toshiba ACPI driver have been
determined. When running at low system load, the minimum of t
2
was t
min
= 0ms and
the maximum was t
max
= 5ms. The result of the 12
th
pass—which is the minimum—is a
measurement error since it equals 0ms. This would indicate that there has been no delay
between the kernel driver and the user space application. At high system load the results for
the Toshiba ACPI driver are: t
min
= 1ms and t
max
= 16ms. The average time interval is
t
avg
= 7.57ms. Figure 6.4 shows the results.
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49
0
2
4
6
8
10
12
14
16
18
Pass
/ ms
High Load
Low Load
2
t
Figure 6.4: Toshiba ACPI Event Time Interval
The performance requirements (Chapter 3, §3.3) specify that the time between a user action
and the arrival of the input event at the user space application should not exceed the limit
of 25 milliseconds. To verify this requirement, t
total
has to be calculated. For the keyboard
driver and the ACPI button driver—they are both interrupt-driven—a worst case assumption
t
1
= 2ms is made. The Toshiba ACPI driver uses polling. Hence, t
1
depends on the polling
frequency and no general assumption for t
1
can be made. Together with the values for t
2
determined by the measurement series, t
total
can b e calculated. To determine whether the