Debug Test Access Port
ARM DDI 0301H Copyright © 2004-2009 ARM Limited. All rights reserved. 14-31
ID012310 Non-Confidential, Unrestricted Access
RTI
1. Go through Run-Test/Idle DBGTAPSM state. This forces the execution of the instruction
currently loaded into the ITR, provided the execute ARM instruction enable bit,
DSCR[13], is set, the Ready flag was captured as set, and the sticky precise Data Abort
flag is cleared.
14.8.2 General setup
You must setup the following control bits before DBGTAP debugging can take place:
• DSCR[14] Debug-mode select bit must be set to 1.
• DSCR[6] sticky precise Data Abort flag must be cleared down, so that aborts are not
detected incorrectly immediately after startup.
The DSCR must be read, the DSCR[14] bit set, and the new value written back. The action of
reading the DSCR automatically clears the DSCR[6] sticky precise Data Abort flag. All
individual breakpoints, watchpoints, and vector catches reset disabled on power-up.
14.8.3 Forcing the processor to halt
Scan the Halt instruction into the DBGTAP controller IR and go through Run-Test/Idle.
14.8.4 Entering Debug state
To enter Debug state you must:
1. Check whether the core has entered Debug state, as follows:
SCAN_N 1 ; select DSCR
INTEST
LOOP
DATAOUT readDSCR
UNTIL readDSCR[0]==1 ; until Core Halted bit is set
2. Save DSCR, as follows:
DATAOUT readDSCR
Save value in readDSCR
3. Save wDTR, in case it contains some data, as follows:
SCAN_N 5 ; select DTR
INTEST
DATA 0x00000000 Valid wDTR
If Valid==1 then Save value in wDTR
4. Set the DSCR[13] execute ARM instruction enable bit, so instructions can be issued to the
core from now:
SCAN_N 1 ; select DSCR
EXTEST
DATA modifiedDSCR ; modifiedDSCR equals readDSCR with bit
; DSCR[13] set
5. Before executing any instruction in Debug state you have to drain the write buffer. This
ensures that no imprecise Data Aborts can return at a later point:
SCAN_N 4 ; select ITR
INST MCR p15,0,Rd,c7,c10,4 ; Data Synchronization Barrier
LOOP
LOOP
SCAN_N 4 ; select DTR
To Next Page
Loading...
Need help?
General
