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Bootloader Features
181
SPRUI07–March 2020
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Boot ROM
Example 2-3. Data Stream Structure 16-bit
10AA ; 0x10AA 16-bit key value
0000 0000 0000 0000 ; 8 reserved words
0000 0000 0000 0000
003F 8000 ; 0x003F8000 EntryAddr, starting point after boot load completes
0005 ; 0x0005 - First block consists of 5 16-bit words
003F 9010 ; 0x003F9010 - First block will be loaded starting at 0x3F9010
0001 0002 0003 0004 ; Data loaded = 0x0001 0x0002 0x0003 0x0004 0x0005
0005
0002 ; 0x0002 - 2nd block consists of 2 16-bit words
003F 8000 ; 0x003F8000 - 2nd block will be loaded starting at 0x3F8000
7700 7625 ; Data loaded = 0x7700 0x7625
0000 ; 0x0000 - Size of 0 indicates end of data stream
After load has completed the following memory values will have been initialized as follows:
Location Value
0x3F9010 0x0001
0x3F9011 0x0002
0x3F9012 0x0003
0x3F9013 0x0004
0x3F9014 0x0005
0x3F8000 0x7700
0x3F8001 0x7625
PC Begins execution at 0x3F8000
In 8-bit mode, the least significant byte (LSB) of the word is sent first followed by the most significant byte
(MSB). For 32-bit values, such as a destination address, the most significant word (MSW) is loaded first,
followed by the least significant word (LSW). The bootloaders take this into account when loading an 8-bit
data stream. Table 2-5 and Example 2-4 show the structure of the incoming data stream to the bootloader.
Table 2-5. LSB/MSB Loading Sequence in 8-bit Data Stream
Byte
Contents
LSB (First Byte of 2) MSB (Second Byte of 2)
1 2 LSB: AA (KeyValue for memory width = 8 bits) MSB: 08h (KeyValue for memory width = 8 bits)
3 4 LSB: Register initialization value or reserved MSB: Register initialization value or reserved
5 6 LSB: Register initialization value or reserved MSB: Register initialization value or reserved
7 8 LSB: Register initialization value or reserved MSB: Register initialization value or reserved
...
...
...
...
...
...
...
...
17 18 LSB: Register initialization value or reserved MSB: Register initialization value or reserved
19 20 LSB: Upper half of Entry point PC[23:16] MSB: Upper half of entry point PC[31:24] (Always 0x00)
21 22 LSB: Lower half of Entry point PC[7:0] MSB: Lower half of Entry point PC[15:8]
23 24 LSB: Block size in words of the first block to load. If the
block size is 0, this indicates the end of the source
program. Otherwise another block follows. For example, a
block size of 0x000A would indicate 10 words or 20 bytes
in the block.
MSB: block size
25 26 LSB: MSW destination address, first block Addr[23:16] MSB: MSW destination address, first block Addr[31:24]
27 28 LSB: LSW destination address, first block Addr[7:0] MSB: LSW destination address, first block Addr[15:8]
29 30 LSB: First word of the first block being loaded MSB: First word of the first block being loaded
...
...
...
...
...
...
...
...
. . LSB: Last word of the first block to load MSB: Last word of the first block to load
. . LSB: Block size of the second block MSB: Block size of the second block
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