X-Git-Url: http://git.mutantstargoat.com/user/nuclear/?a=blobdiff_plain;f=src%2Fboot%2Fboot.s;h=4ab605c7f43be867016e38bf749537ab4695f41e;hb=201a6c7cbc9a6fc7f7d4126cd4e41eff658818a3;hp=e3fd206ba416396c23b0df24bb4e83772437d19c;hpb=e5b5905eb3134a409638a5a20462000ef159e1e6;p=bootcensus diff --git a/src/boot/boot.s b/src/boot/boot.s index e3fd206..4ab605c 100644 --- a/src/boot/boot.s +++ b/src/boot/boot.s @@ -1,37 +1,338 @@ .code16 .section .boot,"a" - mov $0x13, %ax - int $0x10 - - mov $1, %al - mov $0x3c8, %dx - outb %al, %dx - mov $0x3c9, %dx - mov $63, %al - outb %al, %dx - xor %al, %al - outb %al, %dx - outb %al, %dx - - mov $200, %ebx - mov $0x00000101, %eax - pushl $0xa000 - popl %es - xor %di, %di -fill: - mov %ebx, %ecx - and $1, %ecx - jnz 0f - rol $16, %eax -0: mov $80, %ecx - rep stosl - dec %ebx - jnz fill + .set scratchbuf, 0x7b00 +boot: cli + cld + # move stack to just below the code + xor %ax, %ax + mov %ax, %ss + mov $0x7b00, %sp + # use the code segment for data access + mov %cs, %ax + mov %ax, %ds + mov %ax, %es + + mov %dl, drive_number + + call setup_serial + + # load the second stage boot loader and jump to it + mov $_boot2_size, %eax + mov %eax, %ebx + shr $9, %eax + and $0x1ff, %ebx + jz 0f + inc %ax +0: pushw %ax + pushw $1 + # set es to the start of the destination buffer to allow reading in + # full 64k chunks + mov $boot2_addr, %bx + shr $4, %bx + mov %bx, %es + xor %bx, %bx + call read_sectors + jmp boot2_addr + + .set SECT_PER_TRACK, 18 + + .set ARG_NSECT, 6 + .set ARG_SIDX, 4 + +# read_sectors(first, num) +read_sectors: + push %bp + mov %sp, %bp + + mov ARG_SIDX(%bp), %ax + xor %cx, %cx + + jmp 1f +0: push %ax + call read_sector + pop %ax + inc %ax + inc %cx +1: cmp ARG_NSECT(%bp), %cx + jnz 0b + + pop %bp + ret + + .set VAR_ATTEMPTS, -2 +str_rdsec_msg: .asciz "rdsec: " +str_cyl_msg: .asciz " C " +str_head_msg: .asciz " H " +str_sec_msg: .asciz " S " + +# read_sector(sidx) +read_sector: + push %bp + mov %sp, %bp + sub $2, %sp + push %cx + push %dx + + movw $3, VAR_ATTEMPTS(%bp) + +.Lread_try: + # calculate the track (sidx / sectors_per_track) + mov 4(%bp), %ax + mov $str_rdsec_msg, %si + call print_str_num16 + + xor %dx, %dx + mov $SECT_PER_TRACK, %cx + div %cx + mov %ax, %cx + # save the remainder in ax + mov %dx, %ax + # head in dh + mov %cl, %dh + and $1, %dh + # cylinder (track/2) in ch [0-7] and cl[6,7]<-[8,9] + rol $7, %cx + ror $2, %cl + and $0xc0, %cl + # sector num cl[0-5] is sidx % sectors_per_track (saved in ax) + inc %al + or %al, %cl + + mov $str_cyl_msg, %si + mov %cx, %ax + rol $2, %al + and $3, %al + ror $8, %ax + call print_str_num16 + + mov $str_head_msg, %si + xor %ax, %ax + mov %dh, %al + call print_str_num16 + + mov $str_sec_msg, %si + mov %cl, %al + and $0x3f, %ax + call print_str_num16 + + # ah = 2 (read), al = 1 sectors + mov $0x0201, %ax + movb drive_number, %dl + int $0x13 + jnc .Lread_ok + + # abort after 3 attempts + decw VAR_ATTEMPTS(%bp) + jz .Lread_fail + + # error detected, reset controller and retry + xor %ah, %ah + int $0x13 + jmp .Lread_try + +.Lread_fail: + mov 4(%bp), %ax + jmp abort_read + +.Lread_ok: + # DBG print first dword + mov $str_read_error + 4, %si + mov %es:(%bx), %eax + call print_str_num + + # increment es:bx accordingly (advance es if bx overflows) + add $512, %bx + jno 0f + mov %es, %ax + add $4096, %ax + mov %ax, %es + +0: pop %dx + pop %cx + add $2, %sp + pop %bp + ret + +str_read_error: .asciz "err read sect: " + +abort_read: + mov $str_read_error, %si + call print_str_num16 hlt +cursor_x: .byte 0 + + # prints a string (ds:si) followed by a number (eax) +print_str_num: + push %eax + call print_str + pop %eax + call print_num + mov $13, %al + call ser_putchar + mov $10, %al + call ser_putchar + ret + +print_str_num16: + push %eax + and $0xffff, %eax + call print_str_num + pop %eax + ret + + # expects string pointer in ds:si +print_str: + push %es + pusha + + pushw $0xb800 + pop %es + xor %di, %di + movb $0, cursor_x + + push %si + +0: mov (%si), %al + mov %al, %es:(%di) + movb $7, %es:1(%di) + inc %si + add $2, %di + incb cursor_x + cmp $0, %al + jnz 0b + + pop %si + call ser_putstr + + popa + pop %es + ret + + # expects number in eax +print_num: + # save registers + push %es + pusha + + xor %cx, %cx + movw $scratchbuf, %si + mov $10, %ebx + +0: xor %edx, %edx + div %ebx + add $48, %dl + mov %dl, (%si) + inc %si + inc %cx + cmp $0, %eax + jnz 0b + + # print the backwards string + pushw $0xb800 + pop %es + movb cursor_x, %al + xor %ah, %ah + shl $1, %ax + mov %ax, %di + +0: dec %si + mov (%si), %al + movb %al, %es:(%di) + call ser_putchar + inc %di + mov $7, %al + movb %al, %es:(%di) + inc %di + dec %cx + jnz 0b + + # restore regs + popa + pop %es + ret + + .set UART_DATA, 0x3f8 + .set UART_DIVLO, 0x3f8 + .set UART_DIVHI, 0x3f9 + .set UART_FIFO, 0x3fa + .set UART_LCTL, 0x3fb + .set UART_MCTL, 0x3fc + .set UART_LSTAT, 0x3fd + .set DIV_9600, 115200 / 9600 + .set LCTL_8N1, 0x03 + .set LCTL_DLAB, 0x80 + .set FIFO_ENABLE, 0x01 + .set FIFO_SEND_CLEAR, 0x04 + .set FIFO_RECV_CLEAR, 0x02 + .set MCTL_DTR, 0x01 + .set MCTL_RTS, 0x02 + .set MCTL_OUT2, 0x08 + .set LST_TREG_EMPTY, 0x20 + +setup_serial: + # set clock divisor + mov $LCTL_DLAB, %al + mov $UART_LCTL, %dx + out %al, %dx + mov $DIV_9600, %ax + mov $UART_DIVLO, %dx + out %al, %dx + shr $8, %ax + mov $UART_DIVHI, %dx + out %al, %dx + # set format 8n1 + mov $LCTL_8N1, %al + mov $UART_LCTL, %dx + out %al, %dx + # clear and enable fifo + mov $FIFO_ENABLE, %al + or $FIFO_SEND_CLEAR, %al + or $FIFO_RECV_CLEAR, %al + mov $UART_FIFO, %dx + out %al, %dx + # assert RTS and DTR + mov $MCTL_DTR, %al + or $MCTL_RTS, %al + or $MCTL_OUT2, %al + mov $UART_MCTL, %dx + out %al, %dx + ret + + # expects a character in al +ser_putchar: + push %dx + + mov %al, %ah + # wait until the transmit register is empty + mov $UART_LSTAT, %dx +0: in %dx, %al + and $LST_TREG_EMPTY, %al + jz 0b + mov $UART_DATA, %dx + mov %ah, %al + out %al, %dx + + pop %dx + ret + + # expects a string in ds:si +ser_putstr: + mov (%si), %al + cmp $0, %al + jz 0f + call ser_putchar + inc %si + jmp ser_putstr +0: ret + + +drive_number: .byte 0 .org 510 .byte 0x55 .byte 0xaa + +boot2_addr: