blob: 331154166d906b54d0eeb8f685803ef789b1e1c9 [file] [log] [blame]
If you are experiencing hangups/data-aborts when trying to display a BMP image,
the following might be relevant to your situation...
Some architectures cannot handle unaligned memory accesses, and an attempt to
perform one will lead to a data abort. On such architectures it is necessary to
make sure all data is properly aligned, and in many situations simply choosing
a 32 bit aligned address is enough to ensure proper alignment. This is not
always the case when dealing with data that has an internal layout such as a
BMP image:
BMP images have a header that starts with 2 byte-size fields followed by mostly
32 bit fields. The packed struct that represents this header can be seen below:
typedef struct bmp_header {
/* Header */
char signature[2];
__u32 file_size;
__u32 reserved;
__u32 data_offset;
... etc
} __attribute__ ((packed)) bmp_header_t;
When placed in an aligned address such as 0x80a00000, char signature offsets
the __u32 fields into unaligned addresses (in our example 0x80a00002,
0x80a00006, and so on...). When these fields are accessed by U-Boot, a 32 bit
access is generated at a non-32-bit-aligned address, causing a data abort.
The proper alignment for BMP images is therefore: 32-bit-aligned-address + 2.