| ??? 04/06/05 06:30 Read: times |
#91083 - Not relevant to 8051 Responding to: ???'s previous message |
Kuldeep Singh said:
it is a bit offline question do not know wheather should be posted on this forum or not It is off-topic for this forum, as it is not relevant to an 8051 - because it's an 8-bit processor. It is only relevant to processors with larger word sizes - 16, 32, 64 bit, etc. eg, on a 16-bit system, each memory location is effectively 16 bits wide: 1st 16-bit location is at address 0x0000; 2nd 16-bit location is at address 0x0002; 3rd 16-bit location is at address 0x0004; etc Clearly you will cause such a processor a problem if you locate, say, a 16-bit 'int' on an odd address - because one byte will be in one half of one 16-bit location, and the other byte will be in one half of the next 16-bit location! Such processors will have ways & means to cope with this, but it will involve such things as reading the bytes individually & then reconstructing the proper-sized data object. Clearly this gives a major performance hit! for example a code of line "int x_attribute((aligned((16))=0" causes the compiler to allocate the global variable x on a 16byte boundary. It just means that the address must be an integer multiple of 16; ie, 0x0000, 0x0010, 0x0020, 0x0030, etc - in fact any address in which the four least-significant bits are all zero (ie, the least significant hex digit is zero). I think Intel refer to this as a "Paragraph" in relation to the x86? i know for fastest operation variables are aligned according to their size See above. |
| Topic | Author | Date |
| alignment of variable in c | 01/01/70 00:00 | |
| Modulo 16 | 01/01/70 00:00 | |
| thanks smith | 01/01/70 00:00 | |
| Addressing | 01/01/70 00:00 | |
| Not relevant to 8051 | 01/01/70 00:00 | |
| re not relevant | 01/01/70 00:00 | |
| This subject could be relevant.... | 01/01/70 00:00 | |
| yeah right | 01/01/70 00:00 | |
| External Influences | 01/01/70 00:00 | |
| Alignment/byte ordering matters a lot! | 01/01/70 00:00 | |
| you can not align when ... | 01/01/70 00:00 | |
| good references | 01/01/70 00:00 | |
RTFM! | 01/01/70 00:00 |