PC912XDP512F0MPVR datasheet(783/1348 Pages) FREESCALE

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Chapter 20 S12X Debug (S12XDBGV3) Module

MC9S12XDP512 Data Sheet, Rev. 2.21

Freescale Semiconductor

785

20.4.7.4

Breakpoints Via TAGHI Or TAGLO Pin Taghits

Tagging using the external TAGHI/TAGLO pins always ends the session immediately at the tag hit. It is

always end aligned, independent of internal channel trigger alignment conﬁguration.

20.4.7.5

Auxilliary Breakpoint Input

When this signal asserts tracing is terminated and an immediate forced breakpoints are generated,

depending on the conﬁguration of DBGBRK bits.

20.4.7.6

S12XDBG Breakpoint Priorities

XGATE software breakpoints have the highest priority. Active tracing sessions are terminated

immediately.

If a TRIG trigger occurs after Begin or Mid aligned tracing has already been triggered by a comparator

instigated transition to Final State, then TRIG no longer has an effect. When the associated tracing session

is complete, the breakpoint occurs. Similarly if a TRIG is followed by a subsequent trigger from a

comparator channel whose BRK = 0, it has no effect, since tracing has already started.

If a comparator tag hit occurs simultaneously with an external TAGHI/TAGLO hit, the state sequencer

enters state0. TAGHI/TAGLO triggers are always end aligned, to end tracing immediately, independent of

the tracing trigger alignment bits TALIGN[1:0].

If a forced and tagged breakpoint coincide, the forced breakpoint occurs too late to prevent the tagged

instruction being loaded into the execution unit. Conversely the taghit is too late to prevent the breakpoint

request in the DBG module. Thus the S12XCPU suppresses the taghit although the tagged instruction is

executed.

Considering the code example below the forced breakpoint is requested when the location COUNTER is

accessed. This is signalled to the S12XCPU when the next (tagged) instruction (NOP) is already in the

execution stage, thus the tagged instruction is carried out but the tagged breakpoint is suppressed. Reading

the PC with BDM READ_PC returns $C008

c000 cf ff 00

START

LDS

#$FF00

c003 a7

NOP

c004 72 70 08

INC

COUNTER ; Forced breakpoint location = COUNTER

c007 a7

MARK

NOP

; Tagged opcode location = MARK

BGND

[BDM firmware commands]

c008 20 01

BRA

END ; 1st instruction on return from BDM

20.4.7.6.1

S12XDBG Breakpoint Priorities And BDM Interfacing

Breakpoint operation is dependent on the state of the S12XBDM module. If the S12XBDM module is

active, the S12XCPU is executing out of BDM ﬁrmware and S12X breakpoints are disabled. In addition,

while executing a BDM TRACE command, tagging into BDM is disabled. If BDM is not active, the

breakpoint will give priority to BDM requests over SWI requests if the breakpoint happens to coincide

with a SWI instruction in the user’s code. On returning from BDM, the SWI from user code gets executed.

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