| 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. |
