##### Syntax

-H section,...=method

##### Description

This option generates checksums of the sections in the section list into the CHECKSUM segment. Only the used content of the section is checksummed, not any of the unused part.

The method can be one of:

- sum A simple sum of all the data items.
- lrc or xor A longitudinal redundancy check of the data bytes, that is all bytes are exclusive-ored together.
- crc16 A CRC16 of the data using the generating polynomial 0x11021.
- crc32 A CRC32 of the data using the generating polynomial 0x104C11DB7.

##### Setting this in CrossStudio

- Select the project in the Project Explorer.
- In the Linker Options group edit the Checksum Sections property.

The Checksum Sections property is a list of comma-separated sections followed by '=' followed by the checksum method. If the method is omitted, CRC16 is assumed.

##### Example

To checksum the CODE and CONST sections using CRC16:

    -HCODE,CONST=crc16

The CHECKSUM section generated by the linker for this will be as if the following assembly code had been written:

            .PSECT "CHECKSUM"

    ___begin_CHECKSUM:

    ; CODE secion range and checksum
            DW      ___begin_CODE
            DW      ___end_CODE
    ___checksum_CODE::
            DW      crc-of-CODE-section

    ; CONST section range and checksum
            DW      ___begin_CONST
            DW      ___end_CONST
    ___checksum_CONST::
            DW      crc-of-CONST-section

    ; Sentinel
            DW      0
            DW      0
    ___end_CHECKSUM:

Note that the order of the checksums in the CHECKSUM section is undefined, so do not assume the order chosen by the linker will remain fixed. Always access the checksums using the public labels provided.

You can verify the individual checksums of the CODE and CONST sections checksummed above by using code along the following lines:

    // External, provided as source code in the "src" directory
    unsigned int __checksum_crc16(unsigned char *begin, unsigned char *end);

    // Symbols generated by the linker to delimit the CODE and CONST sections
    extern unsigned char __start_CODE[], __end_CODE[];
    extern unsigned char __start_CONST[], __end_CONST[];

    // Symbols generated by the linker for the CODE and CONST checksums
    extern unsigned int __checksum_CODE, __checksum_CONST;

    void main(void)
    {
      assert(__checksum_crc16(__start_CODE, __end_CODE) == __checksum_CODE);
      assert(__checksum_crc16(__start_CONST, __end_CONST) == __checksum_CONST);
    }

However, because the linker generates a table that has the addresses of the ranges checksummed and the expected checksum, you can check all the checksummed regions very simply:

    // External, provided as source code in the "src" directory
    unsigned int __checksum_crc16(unsigned char *begin, unsigned char *end);

    typedef struct {
      unsigned char *begin;
      unsigned char *end;
      unsigned int checksum;
    } checksum_info;

    // Symbols generated by the linker for the CHECKSUM section
    extern checksum_info __begin_CHECKSUM[];

    void main(void)
    {
      checksum_info *p;
      for (p = __begin_CHECKSUM; p->begin || p->end; ++p)
        assert(__checksum_crc16(p->begin, p->end) == p->checksum);
    }