bootloader需要知道的 ：HEX格式 + 如何理解分散加载
如何理解分散加载？
怎么知道自己的函数是否真的分散加载成功了。就看那个map文件。就知道自己写的函数是否是真在ram中运行。
对于HEX格式的校验网上有软件可以算校验值。
Byte COUNT 字节个数 估计是可以换成别的值，比如0x20。这样做的目的可能是一次性向falsh烧写较多字节。但这么弄总感觉有点没有必要。
=========================================================================
http://www.cnblogs.com/imapla/archive/2013/03/16/2926133.html
什么是 Intel HEX 文件格式
Intel HEX 文件是遵循 Intel HEX 文件格式的 ASCII 文本文件。在 Intel HEX 文件的每一行都包含了一个 HEX 记录。这些记录是由一些代表机器语言代码和常量的16进制数据组成的。Intel HEX 文件常用来传输要存储在 ROM 或者 EPROM 中的程序和数据。大部分的 EPROM 编程器能使用 Intel HEX 文件。
Intel HEX由任意数量的十六进制记录组成。每个记录包含5个域，它们按以下格式排列：
Start Code 每个 Intel HEX 记录都由冒号开头
Byte count 是数据长度域，它代表记录当中数据字节的数量
Address 是地址域，它代表记录当中数据的起始地址
Record type 是代表HEX记录类型的域，它可能是以下数据当中的一个：
00-数据记录
01-文件结束记录
02-扩展段地址记录
03-开始段地址记录
04-扩展线性地址记录
05-开始线性地址记录
Data 是数据域，一个记录可以有许多数据字节.记录当中数据字节的数量必须和数据长度域中指定的数字相符
Checksum 是校验和域，它表示这个记录的校验和.校验和的计算是通过将记录当中所有十六进制编码数字对的值相加，以256为模进行以下补足。
详见：http://en.wikipedia.org/wiki/Intel_HEX
The format is a text file, with each line containing hexadecimal values encoding a sequence of data and their starting offset or absolute address.
Each line of Intel HEX file consists of six parts:
- Start code, one character, an ASCII colon ':'.
- Byte count, two hex digits, a number of bytes (hex digit pairs) in the data field. 16 (0x10) or 32 (0x20) bytes of data are the usual compromise values between line length and address overhead.
- Address, four hex digits, a 16-bit address of the beginning of the memory position for the data. Limited to 64 kilobytes, the limit is worked around by specifying higher bits via additional record types. This address is big endian.
- Record type, two hex digits, 00 to 05, defining the type of the data field.
- Data, a sequence of n bytes of the data themselves, represented by 2n hex digits.
- Checksum, two hex digits - the least significant byte of the two's complement of the sum of the values of all fields except fields 1 and 6 (Start code ":" byte and two hex digits of the Checksum). It is calculated by adding together the hex-encoded bytes (hex digit pairs), then leaving only the least significant byte of the result, and making a 2's complement (either by subtracting the byte from 0x100, or inverting it by XOR-ing with 0xFF and adding 0x01). If you are not working with 8-bit variables, you must suppress the overflow by AND-ing the result with 0xFF. The overflow may occur since both 0x100-0 and (0x00 XOR 0xFF)+1 equal 0x100. If the checksum is correctly calculated, adding all the bytes (the Byte count, both bytes in Address, the Record type, each Data byte and the Checksum) together will always result in a value wherein the least significant byte is zero (0x00).
For example, on :0300300002337A1E
03 + 00 + 30 + 00 + 02 + 33 + 7A = E2, 2's complement is 1E
There are six record types:
- 00, data record, contains data and 16-bit address. The format described above.
- 01, End Of File record. Must occur exactly once per file in the last line of the file. The byte count is 00 and the data field is empty. Usually the address field is also 0000, in which case the complete line is ':00000001FF'. Originally the End Of File record could contain a start address for the program being loaded, e.g. :00AB2F0125 would cause a jump to address AB2F. This was convenient when programs were loaded from punched paper tape.
- 02, Extended Segment Address Record, segment-base address (two hex digit pairs in big endian order). Used when 16 bits are not enough, identical to 80x86 real mode addressing. The address specified by the data field of the most recent 02 record is multiplied by 16 (shifted 4 bits left) and added to the subsequent data record addresses. This allows addressing of up to a megabyte of address space. The address field of this record has to be 0000, the byte count is 02 (the segment is 16-bit). The least significant hex digit of the segment address is always 0.
- 03, Start Segment Address Record. For 80x86 processors, it specifies the initial content of the CS:IP registers. The address field is 0000, the byte count is 04, the first two bytes are the CS value, the latter two are the IP value.
- 04, Extended Linear Address Record, allowing for fully 32 bit addressing (up to 4GiB). The address field is 0000, the byte count is 02. The two data bytes (two hex digit pairs in big endian order) represent the upper 16 bits of the 32 bit address for all subsequent 00 type records until the next 04 type record comes. If there is not a 04 type record, the upper 16 bits default to 0000. To get the absolute address for subsequent 00 type records, the address specified by the data field of the most recent 04 record is added to the 00 record addresses.
- 05, Start Linear Address Record. The address field is 0000, the byte count is 04. The 4 data bytes represent the 32-bit value loaded into the EIP register of the 80386 and higher CPU.