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Boot Assist Module (BAM)
MPC5644A Microcontroller Reference Manual, Rev. 6
630
Freescale Semiconductor
The steps to enable the debug port on a censored device are as follows:
1. After the RSTOUT pin has is negated, hold the device in system reset state using a debugger or
other tool.
2. While the device is being held in system reset state shift the 64-bit password into the
Section 36.4.1.4, CENSOR_CTRL Register
) via the JTAG port
using the JTAG ENABLE_CENSOR_CTRL instruction. The JTAG serial password is compared
against the serial boot flash password from the flash shadow block.
3. If there is a match the Nexus client TAP controller enters normal operation mode and the flag
SIU_CCR[DISNEX] is negated, indicating Nexus is enabled. Upon negation of reset the debug /
calibration tool is able to access the device via NEXUS port and JTAG. If the JTAG serial password
does not match the serial boot flash password or the serial boot flash password is an illegal
password then the debug / calibration tool is not able to access the device.
After the debug port is enabled, the tool can access the censored device and can erase and
reprogram the shadow flash block in order to uncensor the device.
NOTE
If the shadow flash block is erased without reprogramming a new valid
password before a reset it will contain an illegal password and the debug
port will be inaccessible.
4. Subsequent resets will clear the JTAG censor password register and the Nexus client TAP
controller will hold in reset again. Therefore, the tool must resend the JTAG serial password, as
described above, in order to enable the Nexus client TAP controller again.
21.5.5
Serial boot mode
When the BAM program transitions to the Serial Boot mode, unused message buffers in CAN_A are used
for the BAM program stack and variables and the SWT watchdog is reprogrammed with timeperiod
greater than the default value.
The MMU setup depends on the way BAM enters the serial boot mode. If EBI boot mode is taken, the
MMU is set up for that mode (see
). The serial boot mode can run in either of two modes of
operation:
•
Standard serial boot mode using fixed baud rates derived from the crystal oscillator used
•
Baud Rate Detection serial boot mode, which allows communication with adaptable speed, based
on measured input signal
The Fixed Baud Rate mode or Baud Rate Detection mode are selected based on the state of the EVTO pin,
recorded in the SIU_RSR[ABR] bit. If the bit is set, the Baud Rate Detection mode is selected if the bit is
cleared, the Fixed Baud Rate is selected.
SIU_RSR[ABR] bit reflects the inverted state of the EVTO pin, thus to select Baud Rate Detection mode,
the EVTO pin needs to be driven low.
Содержание MPC5644A
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