
11-2
ColdFire CF4e Core User’s Manual
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Overview
Real-time debug support: BDM requires the processor to be halted, which many
real-time embedded applications cannot do. Debug interrupts let real-time systems
execute a unique service routine that can quickly save key register and variable
contents and return the system to normal operation without halting. External
development systems can access saved data because the hardware supports
concurrent operation of the processor and BDM-initiated commands. In addition,
the option is provided to allow interrupts to occur. See Section 11.6, “Real-Time
Debug Support.”
The Version 2 ColdFire core implemented the original debug architecture, now called
Revision A. Based on feedback from customers and third-party developers, enhancements
have been added to succeeding generations of ColdFire cores. For Revision A, CSR[HRL]
is 0. See Section 11.4.5, “Configuration/Status Register (CSR).”
The Version 3 core implements Revision B of the debug architecture, offering more
flexibility for configuring the hardware breakpoint trigger registers and removing the
restrictions involving concurrent BDM processing while hardware breakpoint registers are
active. For Revision B, CSR[HRL] is 1.
Revision C of the debug architecture more than doubles the on-chip breakpoint registers
and provides an ability to interrupt debug service routines. For Revision C, CSR[HRL] is
2.
Differences between Revision B and C are summarized as follows:
Debug Revision B has separate PST[3:0] and DDATA[3:0] signals.
Debug Revision C adds breakpoint registers and supports normal interrupt request
service during debug. It combines debug signals into PSTDDATA[7:0]
The addition of the memory management unit (MMU) to the baseline architecture requires
corresponding enhancements to the ColdFire debug functionality, resulting in Revision D.
For Revision D, the revision level bit, CSR[HRL], is 3.
With software support, the MMU can provide a demand-paged, virtual address
environment. To support debugging in this virtual environment, the debug enhancements
are primarily related to the expansion of the virtual address to include the 8-bit address
space identifier (ASID). Conceptually, the virtual address is expanded to a 40-bit value:
the 8-bit ASID plus the 32-bit address.
The expansion of the virtual address affects two major debug functions:
The ASID is optionally included in the specification of the hardware breakpoint
registers. As an example, the four PC breakpoint registers are each expanded by 8
bits, so that a specific ASID value may be programmed as part of the breakpoint
instruction address. Likewise, each operand address/data breakpoint register is
expanded to include an ASID value. Finally, new control registers define if and how
the ASID is to be included in the breakpoint comparison trigger logic.
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