I am working on a product based on MPC5668G which would require JTAG not to be accessible in order to protect the firmware. Would it be possible to disable the access to the debug port via firmware?
censorship can be enabled by modifying the content of shadow flash block. The memory address of the censorship control word is 0x00FF_FDE0. By default, the censorship control word is programmed to be 0x55AA_55AA. This results in a device that is not censored and uses a flash-based password for serial-boot mode. The password is at address 0xFF_FDD8. Take a look at reference manual, Table 8-2 on page 245 (8-3): http://www.freescale.com/files/32bit/doc/ref_manual/MPC5668xRM.pdf This table shows the state of flash, nexus and serial password for all modes. Important warning here: if you erase the flash and if you don’t restore the data or if you restore wrong data then the chip can be locked forever after power-down or reset. How to change the shadow flash – it depends on your tools. For example, you can use this procedure: 1. Download whole shadow block into s-record file. 2. Modify the s-record file accordingly. 3. Burn new s-record file into shadow flash. If you use tools from P&E micro then you can find nice example procedure described in this presentation on pages 21-30: http://www.freescale.com/files/ftf_2010/Americas/FTF10_AUT_F0403_PDF.pdf It talks about MPC5643L and switching some bits in shadow flash but the procedure is the same for MPC5668G and censorship modifying. There’s also application note available: http://www.freescale.com/files/32bit/doc/app_note/AN3787.pdf
Retrieving data ...