Freescale Semiconductor PXR4030, Reference Manual

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Boot Assist Module (BAM)
Freescale Semiconductor 9-7
PXR40 Microcontroller Reference Manual, Rev. 1
When enabled by RCHW[SWT, WTE] bits, the watchdog timeout periods are as shown in the Table 9-5 .
Note the following:
• The core WD timeout for 20 and 40 MHz crystal is the same because the PLLCFG[2] pin should
be set for 40 MHz crystal, which has the effect of doubling the PLL input divider.
• The SWT clock source is directly from the crystal oscillator. The core WD is clocked by the PLL.
• The core WD timeouts reported here correspond to the PLL settings after reset. Core WD timeouts
will change as soon as the PLL is programmed with different multipliers.
Table 9-4. RCHW Field Descriptions
Field Description
0–3 Reserved. These bit values are ignored when the halfword is read. Program to 0 for future compatibility.
4
SWT
Software watchdog timer enable. This bit determines if the software watchdog timer is enabled after passing
control to the user application code.
0 Disable software watchdog timer
1 Enable software watchdog timer after reset. The timeout period is 392400 clock cycles (the default SWT
clock is the crystal oscillator).
5
WTE
MCU core watchdog timer enable. This bit determines if the core software watchdog timer is enabled.after
passing control to the user application code.
0 Disable core software watchdog timer
1 Enable core watchdog timer after reset. The timeout period is 2.5*2
17
system clocks.
6
PS0
Port size. Defines the width of the data bus connected to the memory on D_CS0. After system reset, the BAM
changes D_CS0 to a 16-bit port to fetch the RCHW from either 16- or 32-bit external memories. Then the BAM
reconfigures the EBI as a 16- or 32-bit port, depending on this bit.
0 32-bit D_CS0 port size
1 16-bit D_CS0 port size
Note: Used in development bus boot modes only (not available on all packages). Do not clear this bit if the
device only has a 16-bit data bus.
7
VLE
VLE Code Indicator. This bit configures the MMU entries 1-3 coded as Classic Book E instructions or as
Freescale VLE instructions.
0 User code executes as classic Book E code
1 User code executes as Freescale VLE code
8–15
BOOTID
Boot identifier. This field serves two functions:
• Indicates which block in flash memory contains the boot program
• Indicates if the flash memory is programmed (BOOTID=0x5A) or invalid
Table 9-5. Watchdog Timeout vs. Crystal Frequency
1
1
With the PLL in normal mode and crystal oscillator as a reference clock source.
Crystal Frequency (MHz) Core WD Timeout (ms) SWT Timeout (ms)
8 27.3 49
12 18.3 32.7
16 13.7 24.5
20 11 19.6
40 9.8