STMicroelectronics SPC572L series Reference Manual page 1546

Boot Assist Flash (BAF)
The BAF extends the DCF record concept by implementing soft DCF clients. The 64-bit
DCF records include:
•
32-bits of data
•
15-bit chip select field (selects the module which implements the DCF clients)
•
15-bit address field (selects a specific DCF client within the selected module)
•
Parity bit (not used with UTEST DCF records)
•
Stop bit (to indicate the end of DCF record has been reached)
As part of its execution flow, BAF searches through the list of DCF records in UTEST flash
to determine if any of the records are to be processed by BAF.
The search starts at one of two addresses: either the start address of DCF records in
UTEST (DCF Start Record), or the address specified in UTEST (Soft DCF Record Start
Address). If either of the two least significant bits of the 32-bit address stored at the Soft
DCF Record Start Address is set, the default start address at the DCF Start Record is used.
If the two least significant bits are clear, this 32-bit value is assumed to be the start address
of the search.
The default setting of the two least significant bits is 11b (erased value of flash memory is
FFFF_FFFFh). A user may intentionally program a dummy address with the least two
significant bits set in order to disable the search for an alternate address (as the UTEST
block is OTP). Valid search start address must start on a 4-byte boundary.
The DCF record search finishes when a DCF record is read with a STOP bit set. The STOP
bit may be set because that memory location is not programmed yet (so the list can be
added to) or it can be intentionally programmed STOP record to indicate that no more
records are added to the list. BAF does not execute the DCF record with STOP bit set. BAF
parses the STOP bit before parsing the rest of the records.
BAF uses Chip Select 14 (CS14) for BAF DCF clients. For records with CS14 asserted, the
BAF uses the address field (address[14:0]) in DCF records to determine how to process the
32-bits of data. The soft DCF clients programmed by BAF is listed in
The DCF clients which are used for initialization of security watchdog are explained in
Section 52.2.4.2, Security watchdog
A group of four Soft DCF clients is used to provide a mechanism to write configuration
information to address locations. The first DCF client receive 32-bit address information.
The next three DCF Clients receive the data that is to be written to the address contained in
the first client. The three data clients allow 32-, 16- and 8-bit data to be written to the
address in the first client. These four clients can be accessed repeatedly to write whole
string of data to memory.
Another soft DCF client as stated in
DCF record data contains the start address of a subroutine that the BAF calls before it starts
searching for the host boot header and exits to customer application code. The callback
routine can reside anywhere in the CPU address space including the BAF code block or
UTEST. The callback DCF client can be accessed repeatedly in order to execute a callback
sequence.
The serial boot DCF client provides a mechanism using which application can inform BAF to
perform serial boot or boot from internal flash. Details can be viewed in
SER_BOOT_CBACK – BAF serial boot DCF
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configuration.
Table 876 provides a simple callback feature. The soft
client.
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Table 876.
Section 52.2.4.6,