28 lines
1.2 KiB
Plaintext
28 lines
1.2 KiB
Plaintext
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If you are experiencing hangups/data-aborts when trying to display a BMP image,
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the following might be relevant to your situation...
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Some architectures cannot handle unaligned memory accesses, and an attempt to
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perform one will lead to a data abort. On such architectures it is necessary to
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make sure all data is properly aligned, and in many situations simply choosing
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a 32 bit aligned address is enough to ensure proper alignment. This is not
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always the case when dealing with data that has an internal layout such as a
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BMP image:
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BMP images have a header that starts with 2 byte-size fields followed by mostly
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32 bit fields. The packed struct that represents this header can be seen below:
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typedef struct bmp_header {
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/* Header */
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char signature[2];
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__u32 file_size;
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__u32 reserved;
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__u32 data_offset;
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... etc
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} __attribute__ ((packed)) bmp_header_t;
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When placed in an aligned address such as 0x80a00000, char signature offsets
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the __u32 fields into unaligned addresses (in our example 0x80a00002,
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0x80a00006, and so on...). When these fields are accessed by U-Boot, a 32 bit
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access is generated at a non-32-bit-aligned address, causing a data abort.
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The proper alignment for BMP images is therefore: 32-bit-aligned-address + 2.
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