Albatron Technology ARM11/Cortex-A8 user manual Low level Jtag scan chain configuration

bdiGDB for GNU Debugger, BDI2000 (ARM11/Cortex-A8) User Manual 31

Low level JTAG scan chain configuration:

Sometimes it is necessary to configure the test access port (TAP) of the target before the ARM debug interface is visible and accessible in the usual way. The BDI supports this configuration in a very ge- neric way via the SCANINIT and SCANPOST configuration commands. Both accept a string that de- fines the JTAG sequences to execute. The following example shows how to use these commands:

; Configure	ICEPick module to make	ARM926 TAP visible
SCANINIT	t1:w1000:t0:w1000:	;toggle TRST
SCANINIT	i6=07:d8=89:i6=02:	;connect and select router
SCANINIT	d32=81000082:	;set IP control
SCANINIT	d32=a018206f:	;configure TAP0
SCANINIT	d32=a018216f:cl5:	;enable TAP0, clock 5 times in RTI
SCANINIT	i10=ffff	;scan bypass
;

;Between SCANINIT and SCANPOST the ARM ICEBreaker is configured

;and the DBGRQ bit in the ARM debug control register is set.

;
SCANPOST	i10=002f:	;IP(router) - ARM(bypass)
SCANPOST	d33=0102000106:	;IP control = SysReset
SCANPOST	i10=ffff	;scan bypass

The following low level JTAG commands are supported in the string. Use ":" between commands.

I<n>=<...	b2b1b0>	write IR, b0 is first scanned
D<n>=<...	b2b1b0>	write DR, b0 is first scanned
		n : the number of bits 1..256
		bx : a data byte, two hex digits
W<n>		wait for n (decimal) micro seconds
T1		assert TRST
T0		release TRST
R1		assert RESET
R0		release RESET
CH<n>		clock TCK n (decimal) times with TMS high
CL<n>		clock TCK n (decimal) times with TMS low

The following diagram shows the parts of the standard reset sequence that are replaced with the SCAN string. Only the appropriate part of the reset sequence is replaced. If only a SCANINIT string is defined, then the standard "post" sequence is still executed.

If (reset mode == hard) Assert reset

Toggle TRST

If (reset mode == hard) Delay for reset time

Execute SCANINIT string

Check if Bypass register(s) present

Read and display ID code

Check if debug module is accessible

If (startup == reset) catch reset exception

If (reset mode == hard) Release reset

Wait until reset is really release

Delay for wake-up time

Execute SCANPOST string

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