When RVI is configured in adaptive clocking mode, it uses a 50MHz internal clock to sample RTCK. RVI toggles TCK when it detects a change in RTCK, which happens approximately 60ns after RTCK changes. TDO is generated by a synthesizable ARM processor after the falling edge of RTCK, and is sampled by RVI at the rising edge of TCK. 
The figure shows how TDO and TCK change after the falling edge of RTCK. tTDO is the time from the falling edge of RTCK to the change in TDO, and it depends on the speed of the target. tTCK is the time from the falling edge of RTCK to the rising edge of TCK, and it depends on the RVI internal sampling rate. If the target is slow (tTDO long) and the RVI internal sampling clock is fast (tTCK short), it is possible that RVI cannot sample TDO correctly because the setup time of TDO before the rising edge of TCK is violated. This can be a problem when connecting to very slow targets such as hardware emulators. The only way to avoid this problem is to reduce the frequency of the RVI internal clock. In RVI v1.1, the frequency of the RVI internal sampling clock is set at 50MHz by RV-Config. This information is written into the file rvi.rvc every time the configuration is saved in RV-Config. It is possible to change this frequency by manually editing rvi.rvc before connecting to the target. The relevant lines are: <?xml version="1.0"?> <?RVConfigUtility MajorVersion = '0' MinorVersion = '0' PatchVersion =
'0'?>
<RVConfigUtility>
<RVConfigModule>
.......
.......
<DataList Type = 'Branch'>
<DataListUID Type = 'User'>0x00000002</DataListUID>
<ClockType Type = 'Int32'>0</ClockType>
<ClockSpeed Type = 'Str'>50000000A</ClockSpeed>
<OtherSpeed Type = 'Str'>10.000 MHz</OtherSpeed>
<Tap_Count Type = 'UInt32'>3</Tap_Count>
........ For example, changing the line <ClockSpeed Type = 'Str'>50000000A</ClockSpeed> into <ClockSpeed Type = 'Str'>100000A</ClockSpeed> sets the internal clock at 100KHz instead of 50MHz.
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