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TMS320C6421
Fixed-Point Digital Signal Processor
SPRS346C–JANUARY 2007–REVISED NOVEMBER 2007
As shown in
Table 3-4
and
Table 3-5
, at device reset the Boot Controller defaults the DSPBOOTADDR to
one of two values based on the boot mode selected. In all boot modes, the C64x+ is immediately released
from reset and begins executing from address location indicated in DSPBOOTADDR.
Internal Bootloader ROM (0x0010 0000):
For most boot modes, the DSPBOOTADDR defaults to the
internal Bootloader ROM so that the DSP can immediately execute the bootloader code in the internal
ROM. The bootloader code decodes the captured BOOTMODE, FASTBOOT, and PLLMS information
(in the BOOTCFG register) to determine the proper boot operation.
Note:
For all boot modes that default to DSPBOOTADDR = 0x0010 0000, the bootloader code
disables all C64x+ cache (L2, L1P, and L1D) so that upon exit from the bootloader code, all C64x+
memories are configured as all RAM. If cache use is required, the application code must explicitly
enable the cache. For more information on boot modes, see
Section 3.4.1
,
Boot Modes
. For more
information on the bootloader, see the
Using the TMS320C642x Bootloader
Application Report
(literature number SPRAAK5).
EMIFA Chip Select Space 2 (0x4200 0000):
The EMIFA ROM Direct Boot in PLL Bypass Mode
(BOOTCFG settings BOOTMODE[3:0] = 0100b, FASTBOOT = 0) is the
only
exception where the
DSPBOOTADDR defaults to the EMIFA Chip Select Space 2. The DSP begins execution directly from
the external ROM at this EMIFA space.
For more information how the bootloader code handles each boot mode, see the
Using the TMS320C642x
Bootloader
Application Report (literature number SPRAAK5).
3.4.1.1
FASTBOOT
When C6421 exits pin reset (RESET or POR released), the PLL Controllers (PLLC1 and PLLC2) default
to PLL Bypass Mode. This means the PLLs are disabled, and the MXI/CLKIN clock input is driving the
chip. All the clock domain divider ratios discussed in
Section 6.3.4
,
C6421 Power and Clock Domains
, still
apply. For example, assume an MXI/CLKIN frequency of 25 MHz—meaning the internal clock source for
EMIFA is at CLKDIV3 domain = 25 MHz/3 = 8.3 MHz, a very slow clock. In addition, the EMIFA registers
are reset to the slowest configuration which translates to very slow peripheral operation/boot.
To optimize boot time, the user should reprogram clock settings via the PLLC as early as possible during
the boot process. The FASTBOOT pin facilitates this operation by allowing the device to boot at a faster
clock rate.
Except for the EMIFA ROM Direct Boot in PLL Bypass Mode (BOOTCFG settings BOOTMODE[3:0] =
0100b, FASTBOOT = 0), all other boot modes default to executing from the Internal Bootloader ROM. The
first action that the bootloader code takes is to decode the boot mode. If the FASTBOOT option is
selected (BOOTCFG.FASTBOOT = 1), the bootloader software begins by programming the PLLC1
(System PLLC) to PLL Mode to give the device a slightly faster operation before fetching code from
external devices. The exact PLL multiplier that the bootloader uses is determined by the PLLMS[2:0]
settings, as shown in
Table 3-5
and
Table 3-6
.
Some boot modes
must
be accompanied with FASTBOOT = 1 so that the corresponding peripheral can
run at a reasonable rate to communicate to the external device(s).
Note:
PLLC2 still stays in PLL Bypass Mode, the bootloader
does not
reconfigure it.
3.4.1.2
Selecting FASTBOOT PLL Multiplier
Table 3-5
and
Table 3-6
show the PLL multipliers used by the bootloader code during fastboot
(FASTBOOT = 1) and the resulting device frequency. The user is responsible for selecting the bootmode
with the appropriate PLL multiplier for their MXI/CLKIN clock source so that the device speed and PLL
frequency range requirements are met. For the PLLC1 Clock Frequency Ranges, see
Table 6-15
,
PLLC1
Clock Frequency Ranges
in
Section 6.7.1
,
PLL1 and PLL2
.
The following are guidelines for PLL output frequency and device speed (frequency):
Device Configurations
72
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