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Improve oSCAN1 documentation 

Signed-off-by: mrv96 <mrv96@users.noreply.github.com>
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mrv96 2022-09-19 23:47:50 +02:00
parent c96a24a307
commit 4b0379fa16
1 changed files with 16 additions and 3 deletions
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19
doc/openocd.texi
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@ -2583,10 +2583,23 @@ and initially asserted reset signals.
@end deffn
@deffn {Command} {ftdi oscan1_mode} on|off
Enable or disable OSCAN1 mode. This mode is intended for use with an adapter,
Enable or disable OScan1 mode. This mode is intended for use with an adapter,
such as the ARM-JTAG-SWD by Olimex, that sits in between the FTDI chip and the
target. The adapter uses the normal JTAG signals to control TCKC and TMSC
(bidirectional) signals used in 2-wire cJTAG.
target. The cJTAG prococol is composed of two wires: TCKC (clock) and TMSC (data).
TMSC is a bidirectional signal which is time-multiplexed alternating TDI, TMS and
TDO. The multiplexing is achieved by a tri-state buffer which puts TMSC in Hi-Z
when the device is supposed to take the control of the line (TDO phase).
The ARM-JTAG-SWD adapter uses standard TRST and TMS signals to control TMSC
direction. TRST is used by the adapter as selector for the multiplexers which set
the JTAG probe in 2-wire mode. Whatever signal is used for this purpose, it must
be defined with the name JTAG_SEL using @command{ftdi layout_signal}. JTAG_SEL is
set to 0 during OScan1 initialization.
Some JTAG probes like the Digilent JTAG-HS2, support cJTAG by using a
separate pin to control when TMS is driven onto TMSC. You can use such
probes by defining the signal TMSC_EN using
@command{ftdi layout_signal TMSC_EN -data <mask>}.
@end deffn
@deffn {Command} {ftdi layout_signal} name [@option{-data}|@option{-ndata} data_mask] [@option{-input}|@option{-ninput} input_mask] [@option{-oe}|@option{-noe} oe_mask] [@option{-alias}|@option{-nalias} name]