TC1796
System Units (Vol. 1 of 2)
Reset and Boot Operation
User’s Manual
4-14
V2.0, 2007-07
Reset, V2.0
4.2.7.1
Normal Boot Options
The normal boot options are invoked when BRKIN is inactive (at high level). The TC1796
has three options for booting into normal operation:
•
Starting code execution from external memory
•
Starting code execution from internal PFLASH
•
Starting code execution from internal SPRAM after a bootstrap loader program has
downloaded a program via a serial interface (ASC0 or CAN).
If a reserved boot selection is detected for HWCFG[3:0] with BRKIN = 1, the TC1796
stops further Boot ROM control operations and enters into an endless loop by executing
a jump instruction to itself (can be aborted by a WDT reset).
Serial Boot via Bootstrap Loader
The bootstrap loader (BSL) is a software part of the Boot ROM which provides a
mechanism to load a program code into the scratchpad RAM (SPRAM) of the PMI. The
program code to be loaded is received serially either via the ASC0 or CAN interfaces.
After loading of the code, the bootstrap loader program jumps directly to address
D400 0000
H
(start address of the PMI scratchpad RAM) and begins executing the
program code that has been loaded. Further details about the BSL are described in
.
External Boot
In external boot modes, code execution is started in external memory via the EBU at a
fixed address (A100 0000
H
). In Alternate Boot Modes, the code start address is defined
by one of the two ABM headers (see
).
In order to access external memory after reset, the EBU must have information about the
type and access mechanism of the external memory. For this purpose, a special external
bus access is executed by the EBU in order to retrieve information about the external
code memory. This access is performed to address offset 0000 0004
H
of the memory
connected to CS0, using access parameters such that regardless of the type and
characteristics of the external memory, configuration information can be read from the
memory into the EBU. By examining this information, the EBU determines the exact
requirements for accesses to the external memory. It then configures the control
registers accordingly, and performs the first instruction fetch from address A100 0000
H
.
All further accesses to external memory during external boot will activate CS0 (until the
EBU becomes reprogrammed for example by a user program).