JTAG control
Note:
UM1250
the other signal sequences are transmitted (and in any future jtag command if not specified).
The initial levels of the TAP signals when switching to manual control of the TAP for the first
time are listed in
Table 105
.
Table 105.
Initial signal levels
Signal Initial level
asebrk ntrst nrst stmmx tck tdo tms triggerout
1
1
1
1
0
0
1
0
Comment
The debug emulation function of the ST40 UDI is activated when notASEBRK is 0.
The TAP is reset when notTRST is 0.
The target is reset when notRESET is 0.
The TAP of the ST MultiCore/MUX is selected when the stmmx signal is set to 0.
The clocking of TCK is assumed to generate a clock signal which first presents a rising-edge for TCK and then a falling-edge for TCK
(guaranteed when in singleshot and continuous modes).
The STMC’s TDO is connected to the target’s TDI.
The TAP is always guaranteed to return to the Test-Logic Reset state after 5 TCK clock cycles when TMS is set to 1.
The STMC’s TRIG_OUT is connected to the target’s TRIG_IN.
The initial signal levels have been chosen to ensure that the target is not affected when
switching to manual control of the TAP signals. When switching from manual mode to any
other mode the TCK signal is always reset to its initial level of 0. In singleshot and continuous
modes, TCK always returns to the initial level of 0 after every clock cycle. All other signals retain their levels when switching between modes.
The ST Micro Connect’s TDI signal from the TDO of the target TAP can be captured by the jtag
command by specifying the tdi subcommand with a GDB convenience variable name template into which the numerical representations of the TDI signal levels are saved.
A target application variable cannot be used directly for capturing the TDI signal as GDB has no access to the ST40 in order to save the captured signal while the TAP is under manual control. Instead a GDB convenience variable can be used to store the captured signal until the mode is returned to normal, at which point the GDB convenience variable can be used to set the target application variable.
The jtag command sets several variables derived from the GDB convenience variable name template, variable, specified by the tdi subcommand.
variable_n
This variable is set to the number of bits required to represent the
TDI signal levels captured by the jtag command. The number of bits indicates the number of 32-bit variables (see below) that were set by the jtag command in order to hold the numerical representation of the captured TDI signal.
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