Datasheet

412
SAM4S Series [DATASHEET]
11100F–ATARM–29-Jan-14
24. SAM4S Boot Program
24.1 Description
The SAM-BA Boot Program integrates an array of programs permitting download and/or upload into the different
memories of the product.
24.2 Hardware and Software Constraints
 SAM-BA Boot uses the first 2048 bytes of the SRAM for variables and stacks. The remaining available size can be
used for user's code.
 USB Requirements:
 External Crystal or External Clock
(1)
with frequency of:
 11,289 MHz
 12,000 MHz
 16,000 MHz
 18,432 MHz
 UART0 requirements: None
Note: 1. Must be 2500 ppm and 1.2V Square Wave Signal.
24.3 Flow Diagram
The Boot Program implements the algorithm in Figure 24-1.
Figure 24-1. Boot Program Algorithm Flow Diagram
The SAM-BA Boot program seeks to detect a source clock either from the embedded main oscillator with external crystal
(main oscillator enabled) or from a supported frequency signal applied to the XIN pin (Main oscillator in bypass mode).
If a clock is found from the two possible sources above, the boot program checks to verify that the frequency is one of the
supported external frequencies. If the frequency is one of the supported external frequencies, USB activation is allowed,
else (no clock or frequency other than one of the supported external frequencies), the internal 12 MHz RC oscillator is
used as main clock and USB clock is not allowed due to frequency drift of the 12 MHz RC oscillator.
Table 24-1. Pins Driven during Boot Program Execution
Peripheral Pin PIO Line
UART0 URXD0 PA9
UART0 UTXD0 PA10
Device
Setup
Character # received
from UART0?
Run SAM-BA Monitor
USB Enumeration
Successful ?
Ye s
Run SAM-BA Monitor
Ye s
No
No