The JTAG chain is configured by the CSU BootROM during boot based on the security state of the boot. The values for the JTAG chain configuration registers for each boot mode are shown in Table: POR Boot State and Secure Boot Mode to Table: Non-secure Boot Mode. The state immediately after a POR is a secure state, but the state changes for non-secure device and PJTAG boot modes.
Table 39-1: POR Boot State and Secure Boot Mode
|
Register
|
Value
|
Description
|
|
JTAG_CHAIN_STATUS
|
0x0
|
Arm DAP and PL TAP are disabled.
|
|
JTAG_DAP_CFG
|
0x0
|
DAP debug disabled.
|
|
JTAG_SEC
|
0x0
|
Security gates enabled.
|
Table 39-2: PJTAG Boot Mode
|
Register
|
Value
|
Description
|
|
JTAG_CHAIN_STATUS (ro)
|
0x1
|
Arm DAP is disabled.
PL TAP is enabled.
|
|
JTAG_DAP_CFG (r/w)
|
0xFF
|
DAP debug enabled (invasive and non-invasive).
|
|
JTAG_SEC (r/w)
|
0x3F
|
Security gates disabled.
|
Table 39-3: Non-secure Boot Mode
|
Register
|
Value
|
Description
|
|
JTAG_CHAIN_STATUS
|
0x3
|
Arm DAP and PL TAP are enabled.
|
|
JTAG_DAP_CFG
|
0x3F
|
DAP debug enabled (invasive and non-invasive).
|
|
JTAG_SEC
|
0x3F
|
Security gates disabled.
|