Freescale Semiconductor MCF54455 Reference Manual page 888

0x80B
0x80E
0x80F
0xC05
1
If an RGPIO module is available on this device.
34.4.1.5.12 BDM Accesses of the Stack Pointer Registers (A7: SSP and USP)
The ColdFire core supports two unique stack pointer (A7) registers: the supervisor stack pointer (SSP) and
the user stack pointer (USP). The hardware implementation of these two programmable-visible 32-bit
registers does not uniquely identify one as the SSP and the other as the USP. Rather, the hardware uses one
32-bit register as the currently-active A7; the other is named the OTHER_A7. Therefore, the contents of
the two hardware registers is a function of the operating mode of the processor:
if SR[S] = 1
then A7 = Supervisor Stack Pointer
OTHER_A7 = User Stack Pointer
else A7 = User Stack Pointer
OTHER_A7 = Supervisor Stack Pointer
The BDM programming model supports reads and writes to A7 and OTHER_A7 directly. It is the
responsibility of the external development system to determine the mapping of A7 and OTHER_A7 to the
two program-visible definitions (supervisor and user stack pointers), based on the SR[S] bit.
34.4.1.5.13 BDM Accesses of the EMAC Registers
The presence of rounding logic in the output datapath of the EMAC requires special care for
BDM-initiated reads and writes of its programming model. In particular, any result rounding modes must
be disabled during the read/write process so the exact bit-wise EMAC register contents are accessed.
For example, a BDM read of an accumulator (ACCx) must be preceded by two commands accessing the
MAC status register, as shown in the following sequence:
BdmReadACCx (
rcreg macsr;
wcreg #0,macsr;
rcreg ACCx;
wcreg #saved_data,macsr;// restore the original macsr
)
Likewise, to write an accumulator register, the following BDM sequence is needed:
BdmWriteACCx (
rcreg macsr;
wcreg #0,macsr;
wcreg #data,ACCx;
wcreg #saved_data,macsr;// restore the original macsr
)
Freescale Semiconductor
Table 34-26. Control Register Map (continued)
Rc
RAM Base Address Register (RAMBAR)
// read current macsr contents and
// disable all rounding modes
// read the desired accumulator
// read current macsr contents and
// disable all rounding modes
// write the desired accumulator
Register Definition
MAC Accumulator 3 (ACC3)
Status Register (SR)
Program Register (PC)
Debug Module
save
save
34-46