mirror of
https://github.com/AsahiLinux/u-boot
synced 2024-11-25 06:00:43 +00:00
28 lines
1.2 KiB
Text
28 lines
1.2 KiB
Text
|
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.
|