I need to bringup a custom i.MX6Q board. The only available boot device is SPI-NOR, so I want to use JTAG to do the initial DDR configuration and to load u-boot.
I am using a J-Link with OpenOCD, and this is successfully talking to the JTAG DAP, including the AHP-AP and the APB-AP. I can read the on-chip ROM and RAM using either AP:
> dap apsel 0
ap 0 selected, identification register 0x44770001
> mdw 0
0x00000000: e59ff01c
> mww 0x907000 0x12345678
> mdw 0x907000
0x00907000: 12345678
>
> dap apsel 1
ap 1 selected, identification register 0x24770002
> mdw 0
0x00000000: e59ff01c
> mww 0x907000 0x87654321
> mdw 0x907000
0x00907000: 87654321
However, there are problems accessing other registers, such as the MMDC:
> dap apsel 0
ap 0 selected, identification register 0x44770001
> mdw 0x21b0000
JTAG-DP STICKY ERROR
MEM_AP_CSW 0x2800052, MEM_AP_TAR 0x21b0000
JTAG-DP STICKY ERROR
MEM_AP_CSW 0x2800052, MEM_AP_TAR 0x21b0000
Block read error address 0x21b0000
in procedure 'mdw'
>
> dap apsel 1
ap 1 selected, identification register 0x24770002
> mdw 0x21b0000
0x021b0000: 03110000
The above shows that access works using the APB-AP, but fails using the AHB-AP.
According to the CoreSight Components TRM (DDI0314H), section 2.7.5, the CSW has Sprot = 0, SPIStatus = 1, DbgStatus = 1, which means "Secure transfer produced an error response".
What are the possible reasons for this error response? Is the processor booting up in some secure state that I need to disable before the AHB-AP is allowed access to the MMDC registers?
Note that I am currently unable to halt the processor immediately after reset, so it is running some of the boot ROM code already.
