TC1796
System Units (Vol. 1 of 2)
CPU Subsystem
User’s Manual
2-7
V2.0, 2007-07
CPU, V2.0
2.3
Implementation-specific Features
This section describes the implementation-specific features of the TC1796 CPU. For a
full description of the TriCore architecture refer to the TriCore 1 Architecture Manual.
2.3.1
Context Save Areas
In the TC1796, Context Save Areas (CSA) must be placed in LDRAM. CSAs should not
be located in the DPRAM (dual-ported RAM).
Refer to the TriCore 1 Architecture Manual Chapter 5 - Tasks and Functions.
2.3.2
Fast Context Switching
The TC1796 uses a uniform context-switching method for function calls, interrupts and
traps. In all cases, the Upper Context of the task is automatically saved and restored by
hardware. Saving and restoring of the Lower Context may be performed optionally by
software.
Fast context switching is enhanced by the unique memory subsystem design. When they
are not full, the shadow registers allow a complete Upper Context to be saved in as few
as two clock cycles. When the shadow registers are full, the upper context save takes
up to five cycles. On the average, an upper context save takes 2.7 cycles. Shadow
registers are automatically restored from memory when required.
2.3.3
Reset System
Several events can cause the TC1796 system to be reset. The CPU does not differ in its
behavior on reset. The status register RST_SR allows the CPU to determine which event
caused the reset. Refer to
of this TC1796 User’s Manual.
2.3.4
Program Counter Register - PC
The Program Counter (PC) holds the address of the instruction that is currently fetched
and forwarded to the CPU pipelines. The CPU handles updates of the PC automatically.
Software can use the current value of the PC for various tasks, such as performing code
address calculations. Reading the PC through software executed by the CPU must only
be done with an MFCR instruction. Explicit writes to the PC through an MTCR instruction
must not be done due to possible unexpected behavior of the CPU.
The CPU must not perform Load/Store instructions to the mapped address of the PC in
Segment 15. A MEM trap will be generated in such a case.
Bit 0 of the PC register is read-only and hard-wired to 0.
Refer to the TriCore 1 Architecture Manual - Core Registers.