avr gcc - Page 53 - Developer IT

What is required to use LODSB in assembly?

- by Harvey

What is the minimum set of steps required to use LODSB to load a relative address to a string in my code? I have the following test program that I'm using PXE to boot. I boot it two ways: via pxelinux.0 and directly. If I boot it directly, my program prints both strings. If I boot via pxelinux.0, it only prints the first string. Why? Working technique (for both): Set the direction flag to increment, cld Set ds to cs Put the address (from start) of string in si Add the starting offset to si Non-working technique (just for pxelinux): Calculate a new segment address based on (((cs << 4) + offset) >> 4) Set ds to that. (either A000 or 07C0) text here to fix bug in markdown // Note: If you try this code, don't forget to set // the "#if 0" below appropriately! .text .globl start, _start start: _start: _start1: .code16 jmp real_start . = _start1 + 0x1fe .byte 0x55, 0xAA // Next sector . = _start1 + 0x200 jmp real_start test1_str: .asciz "\r\nTest: 9020:fe00" test2_str: .asciz "\r\nTest: a000:0000" real_start: cld // Make sure %si gets incremented. #if 0 // When loaded by pxelinux, we're here: // 9020:fe00 ==> a000:0000 // This works. movw $0x9020, %bx movw %bx, %ds movw $(test1_str - _start1), %si addw $0xfe00, %si call print_message // This does not. movw $0xA000, %bx movw %bx, %ds movw $(test2_str - _start1), %si call print_message #else // If we are loaded directly without pxelinux, we're here: // 0000:7c00 ==> 07c0:0000 // This works. movw $0x0000, %bx movw %bx, %ds movw $(test1_str - _start1), %si addw $0x7c00, %si call print_message // This does, too. movw $0x07c0, %bx movw %bx, %ds movw $(test2_str - _start1), %si call print_message #endif // Hang the computer sti 1: jmp 1b // Prints string DS:SI (modifies AX BX SI) print_message: pushw %ax jmp 2f 3: movb $0x0e, %ah /* print char in AL */ int $0x10 /* via TTY mode */ 2: lodsb (%si), %al /* get token */ cmpb $0, %al /* end of string? */ jne 3b popw %ax ret .balign 0x200 Here's the compilation: /usr/bin/ccache gcc -Os -fno-stack-protector -fno-builtin -nostdinc -DSUPPORT_SERIAL=1 -DSUPPORT_HERCULES=1 -DSUPPORT_GRAPHICS=1 -DHAVE_CONFIG_H -I. -Wall -ggdb3 -Wmissing-prototypes -Wunused -Wshadow -Wpointer-arith -falign-jumps=1 -falign-loops=1 -falign-functions=1 -Wundef -g -c -o ds_teststart_exec-ds_teststart.o ds_test.S /usr/bin/ccache gcc -g -o ds_teststart.exec -nostdlib -Wl,-N -Wl,-Ttext -Wl,8000 ds_teststart_exec-ds_teststart.o objcopy -O binary ds_teststart.exec ds_teststart

Search Results

Search found 2264 results on 91 pages for 'avr gcc'.

Page 53/91 | < Previous Page | 49 50 51 52 53 54 55 56 57 58 59 60 | Next Page >

- by Harvey

- by Jake Stevenson

- by Pierre Bourdon

- by robUK

- by Chris

- by glutz78

- by kranthikumar

- by IIIOXIII

- by Alex Farber

- by pythonic metaphor

- by Ockonal

- by wgpubs

- by Nathan

- by khronos666

- by Ockonal

- by Daziplqa

- by lhw

- by wrongusername

- by Julian Kessel

- by prosseek

- by user255403

- by balraj

- by Peter Lee

- by AruniRC

- by mathan

< Previous Page | 49 50 51 52 53 54 55 56 57 58 59 60 | Next Page >