Albatron Technology ARM11/Cortex-A8

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