dsp56800eerm Freescale Semiconductor, Inc, dsp56800eerm Datasheet - Page 124

• Manufacturer Part Number: dsp56800eerm
• Description: 16-bit Digital Signal Controllers
• Manufacturer: Freescale Semiconductor, Inc

7.2 Flash Access Blocking Mechanisms
The 56F8357/56F8157 have several operating functional and test modes. Effective Flash security must
address operating mode selection and anticipate modes in which the on-chip Flash can be compromised
and read without explicit user permission. Methods to block these are outlined in the next subsections.
7.2.1
At boot time, the SIM determines in which functional modes the device will operate. These are:
When Flash security is enabled as described in the Flash Memory module specification, the device will
boot in internal boot mode, disable all access to external P-space, and start executing code from the Boot
Flash at address 0x02_0000.
This security affords protection only to applications in which the device operates in internal Flash security
mode. Therefore, the security feature cannot be used unless all executing code resides on-chip.
When security is enabled, any attempt to override the default internal operating mode by asserting the
EXTBOOT pin in conjunction with reset will be ignored.
7.2.2
On-chip Flash can be read by issuing commands across the EOnCE port, which is the debug interface for
the 56800E core. The TRST, TCLK, TMS, TDO, and TDI pins comprise a JTAG interface onto which the
EOnCE port functionality is mapped. When the device boots, the chip-level JTAG TAP (Test Access Port)
is active and provides the chip’s boundary scan capability and access to the ID register.
Proper implementation of Flash security requires that no access to the EOnCE port is provided when
security is enabled. The 56800E core has an input which disables reading of internal memory via the
JTAG/EOnCE. The FM sets this input at reset to a value determined by the contents of the FM security
bytes.
7.2.3
If a user inadvertently enables Flash security on the device, a built-in lockout recovery mechanism can be
used to reenable access to the device. This mechanism completely reases all on-chip Flash, thus disabling
Flash security. Access to this recovery mechanism is built into CodeWarrior via an instruction in memory
configuration (.cfg) files. Add, or uncomment the following configuration command:
unlock_flash_on_connect 1
For more information, please see CodeWarrior MC56F83xx/DSP5685x Family Targeting Manual.
The LOCKOUT_RECOVERY instruction will have an associated 7-bit Data Register (DR) that is used to
control the clock divider circuit within the FM module. This divider, FM_CLKDIV[6:0], is used to control
the period of the clock used for timed events in the FM erase algorithm. This register must be set with
appropriate values before the lockout sequence can begin. Refer to the JTAG section of the 56F8300
Peripheral User Manual for more details on setting this register value.
124
•
•
•
Internal Boot Mode
External Boot Mode
Secure Mode
Forced Operating Mode Selection
Disabling EOnCE Access
Flash Lockout Recovery
56F8357 Technical Data, Rev. 15
Freescale Semiconductor
Preliminary