kolibrios/kernel/branches/kolibri-cfg/bootloader/fat32/bootsect.txt
CleverMouse 7b2b309d03 kernel branch with configurable boot
git-svn-id: svn://kolibrios.org@1942 a494cfbc-eb01-0410-851d-a64ba20cac60
2011-05-30 10:27:45 +00:00

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×èòàé ìåæäó ñòðîê - òàì íèêîãäà íå áûâàåò îïå÷àòîê.
Áóòñåêòîð äëÿ FAT32-òîìà íà íîñèòåëå ñ ðàçìåðîì ñåêòîðà 0x200 = 512 áàéò.
=====================================================================
Åñòü äâå âåðñèè â çàâèñèìîñòè îò òîãî, ïîääåðæèâàåò ëè íîñèòåëü LBA,
âûáîð îñóùåñòâëÿåòñÿ óñòàíîâêîé êîíñòàíòû use_lba â ïåðâîé ñòðîêå èñõîäíèêà.
Òðåáîâàíèÿ äëÿ ðàáîòû:
1) Ñàì áóòñåêòîð, ïåðâàÿ êîïèÿ FAT è âñå èñïîëüçóåìûå ôàéëû
äîëæíû áûòü ÷èòàáåëüíû. (Åñëè äåëî ïðîèñõîäèò íà íîñèòåëå ñ ðàçáèåíèåì íà
ðàçäåëû è çàãðóçî÷íûé êîä â MBR äîñòàòî÷íî óìíûé, òî ÷èòàáåëüíîñòè ðåçåðâíîé
êîïèè áóòñåêòîðà (ñåêòîð íîìåð 6 íà òîìå) äîñòàòî÷íî âìåñòî ÷èòàáåëüíîñòè
ñàìîãî áóòñåêòîðà).
2) Ìèíèìàëüíûé ïðîöåññîð - 80386.
3) Â ñèñòåìå äîëæíî áûòü êàê ìèíèìóì 584K ñâîáîäíîé áàçîâîé ïàìÿòè.
=====================================================================
Äîêóìåíòàöèÿ â òåìó (ññûëêè ïðîâåðÿëèñü íà âàëèäíîñòü 15.05.2008):
îôèöèàëüíàÿ ñïåöèôèêàöèÿ FAT: http://www.microsoft.com/whdc/system/platform/firmware/fatgen.mspx
â ôîðìàòå PDF: http://staff.washington.edu/dittrich/misc/fatgen103.pdf
ðóññêèé ïåðåâîä: http://wasm.ru/docs/11/fatgen103-rus.zip
îôèöèàëüíàÿ ñïåöèôèêàöèÿ ðàñøèðåíèÿ EDD BIOS 3.0: http://www.phoenix.com/NR/rdonlyres/19FEBD17-DB40-413C-A0B1-1F3F560E222F/0/specsedd30.pdf
òî æå, âåðñèÿ 1.1: http://www.phoenix.com/NR/rdonlyres/9BEDED98-6B3F-4DAC-BBB7-FA89FA5C30F0/0/specsedd11.pdf
îïèñàíèå ôóíêöèé BIOS: Interrupt List by Ralf Brown: http://www.cs.cmu.edu/~ralf/files.html
îôèöèàëüíàÿ ñïåöèôèêàöèÿ Boot BIOS: http://www.phoenix.com/NR/rdonlyres/56E38DE2-3E6F-4743-835F-B4A53726ABED/0/specsbbs101.pdf
=====================================================================
Ñõåìà èñïîëüçóåìîé ïàìÿòè:
...-7C00 ñòåê
7C00-7E00 êîä áóòñåêòîðà
7E00-8200 âñïîìîãàòåëüíûé ôàéë çàãðóç÷èêà (kordldr.f32)
8400-8C00 èíôîðìàöèÿ î êýøå äëÿ òàáëèöû FAT: 100h âõîäîâ ïî 8
áàéò: 4 áàéòà (äâå ññûëêè - âïåð¸ä è íàçàä) äëÿ
îðãàíèçàöèè L2-ñïèñêà âñåõ ïðî÷èòàííûõ ñåêòîðîâ â
ïîðÿäêå âîçðàñòàíèÿ ïîñëåäíåãî âðåìåíè èñïîëüçîâàíèÿ
+ 4 áàéòà äëÿ íîìåðà ñåêòîðà; ïðè ïåðåïîëíåíèè êýøà
âûêèäûâàåòñÿ ýëåìåíò èç ãîëîâû ñïèñêà, òî åñòü òîò,
ê êîòîðîìó äîëüøå âñåõ íå áûëî îáðàùåíèé
60000-80000 êýø äëÿ òàáëèöû FAT (100h ñåêòîðîâ)
80000-90000 òåêóùèé êëàñòåð òåêóùåé ðàññìàòðèâàåìîé ïàïêè
90000-... êýø äëÿ ñîäåðæèìîãî ïàïîê (êàæäîé ïàïêå îòâîäèòñÿ
2000h áàéò = 100h âõîäîâ, îäíîâðåìåííî â êýøå
ìîæåò íàõîäèòüñÿ íå áîëåå 8 ïàïîê;
òî÷íûé ðàçìåð îïðåäåëÿåòñÿ ðàçìåðîì äîñòóïíîé
ôèçè÷åñêîé ïàìÿòè - êàê ïðàâèëî, íåïîñðåäñòâåííî
ïåðåä A0000 ðàçìåùàåòñÿ EBDA, Extended BIOS Data Area)
=====================================================================
Îñíîâíîé ïðîöåññ çàãðóçêè.
Òî÷êà âõîäà (start): ïîëó÷àåò óïðàâëåíèå îò BIOS ïðè çàãðóçêå, ïðè ýòîì
dl ñîäåðæèò èäåíòèôèêàòîð äèñêà, ñ êîòîðîãî èä¸ò çàãðóçêà
1. Íàñòðàèâàåò ñòåê ss:sp = 0:7C00 (ñòåê ðàñïîëàãàåòñÿ íåïîñðåäñòâåííî ïåðåä
êîäîì), ñåãìåíò äàííûõ ds = 0, è óñòàíàâëèâàåò ss:bp íà íà÷àëî
áóòñåêòîðà (â äàëüíåéøåì äàííûå áóäóò àäðåñîâàòüñÿ ÷åðåç [bp+N] -
ýòî îñâîáîæäàåò ds è ýêîíîìèò íà ðàçìåðå êîäà). Ñîõðàíÿåò â ñòåêå
èäåíòèôèêàòîð çàãðóçî÷íîãî äèñêà äëÿ ïîñëåäóþùåãî îáðàùåíèÿ
÷åðåç byte [bp-2].
2. LBA-âåðñèÿ: ïðîâåðÿåò, ïîääåðæèâàåò ëè íîñèòåëü LBA, âûçîâîì ôóíêöèè 41h
ïðåðûâàíèÿ 13h. Åñëè íåò, ïåðåõîäèò íà êîä îáðàáîòêè îøèáîê ñ
ñîîáùåíèåì îá îòñóòñòâèè LBA.
CHS-âåðñèÿ: îïðåäåëÿåò ãåîìåòðèþ íîñèòåëÿ âûçîâîì ôóíêöèè 8 ïðåðûâàíèÿ 13h è
çàïèñûâàåò ïîëó÷åííûå äàííûå ïîâåðõ BPB. Åñëè âûçîâ çàâåðøèëñÿ îøèáêîé,
ïðåäïîëàãàåò óæå ñóùåñòâóþùèå äàííûå êîððåêòíûìè.
3. Âû÷èñëÿåò íà÷àëî äàííûõ FAT-òîìà, ñîõðàíÿåò åãî â ñòåê äëÿ ïîñëåäóþùåãî
îáðàùåíèÿ ÷åðåç dword [bp-10].  ïðîöåññå âû÷èñëåíèÿ óçíà¸ò íà÷àëî
ïåðâîé FAT, ñîõðàíÿåò è åãî â ñòåê äëÿ ïîñëåäóþùåãî îáðàùåíèÿ ÷åðåç
dword [bp-6].
4. (Çàêàí÷èâàÿ òåìó ïàðàìåòðîâ â ñòåêå) Ïîìåùàåò â ñòåê dword-çíà÷åíèå -1
äëÿ ïîñëåäóþùåãî îáðàùåíèÿ ÷åðåç dword [bp-14] - èíèöèàëèçàöèÿ
ïåðåìåííîé, ñîäåðæàùåé òåêóùèé ñåêòîð, íàõîäÿùèéñÿ â êýøå FAT
(-1 íå ÿâëÿåòñÿ âàëèäíûì çíà÷åíèåì äëÿ íîìåðà ñåêòîðà FAT).
5. Èùåò â êîðíåâîé ïàïêå ýëåìåíò kordldr.f32. Åñëè íå íàõîäèò - ïåðåõîäèò íà
êîä îáðàáîòêè îøèáîê ñ ñîîáùåíèåì î íåíàéäåííîì çàãðóç÷èêå.
Çàìå÷àíèå: íà ýòîì ýòàïå çàãðóçêè èñêàòü ìîæíî òîëüêî â êîðíåâîé
ïàïêå è òîëüêî èìåíà, çàäàííûå â ôîðìàòå ôàéëîâîé ñèñòåìå FAT
(8+3 - 8 áàéò íà èìÿ, 3 áàéòà íà ðàñøèðåíèå, âñå áóêâû äîëæíû
áûòü çàãëàâíûìè, ïðè íåîáõîäèìîñòè èìÿ è ðàñøèðåíèå äîïîëíÿþòñÿ
ïðîáåëàìè, ðàçäåëÿþùåé òî÷êè íåò, çàâåðøàþùåãî íóëÿ íåò).
6. Çàãðóæàåò ïåðâûé êëàñòåð ôàéëà kordldr.f32 ïî àäðåñó 0:7E00 è ïåðåäà¸ò
åìó óïðàâëåíèå. Ïðè ýòîì â ðåãèñòðå eax îêàçûâàåòñÿ àáñîëþòíûé
íîìåð ïåðâîãî ñåêòîðà kordldr.f32, à â cx - ÷èñëî ñ÷èòàííûõ ñåêòîðîâ
(ðàâíîå ðàçìåðó êëàñòåðà).
Âñïîìîãàòåëüíûå ïðîöåäóðû áóòñåêòîðà.
Êîä îáðàáîòêè îøèáîê (err):
1. Âûâîäèò ñòðîêó ñ ñîîáùåíèåì îá îøèáêå.
2. Âûâîäèò ñòðîêó "Press any key...".
3. Æä¸ò íàæàòèÿ any key.
4. Âûçûâàåò int 18h, äàâàÿ øàíñ BIOSó ïîïûòàòüñÿ çàãðóçèòüñÿ îòêóäà-íèáóäü åù¸.
5. Äëÿ ïîäñòðàõîâêè çàöèêëèâàåòñÿ.
Ïðîöåäóðà ÷òåíèÿ êëàñòåðà (read_cluster):
íà âõîäå äîëæíî áûòü óñòàíîâëåíî:
ss:bp = 0:7C00
es:bx = óêàçàòåëü íà íà÷àëî áóôåðà, êóäà áóäóò ïðî÷èòàíû äàííûå
eax = íîìåð êëàñòåðà
íà âûõîäå: ecx = ÷èñëî ïðî÷èòàííûõ ñåêòîðîâ (ðàçìåð êëàñòåðà),
es:bx óêàçûâàåò íà êîíåö áóôåðà, â êîòîðûé áûëè ïðî÷èòàíû äàííûå,
eax è ñòàðøèå ñëîâà äðóãèõ 32-áèòíûõ ðåãèñòðîâ ðàçðóøàþòñÿ
Çàãðóæàåò â ecx ðàçìåð êëàñòåðà, ïåðåêîäèðóåò íîìåð êëàñòåðà â íîìåð ñåêòîðà
è ïåðåõîäèò ê ñëåäóþùåé ïðîöåäóðå.
Ïðîöåäóðà ÷òåíèÿ ñåêòîðîâ (read_sectors32 è read_sectors2):
íà âõîäå äîëæíî áûòü óñòàíîâëåíî:
ss:bp = 0:7C00
es:bx = óêàçàòåëü íà íà÷àëî áóôåðà, êóäà áóäóò ïðî÷èòàíû äàííûå
eax = ñòàðòîâûé ñåêòîð (îòíîñèòåëüíî íà÷àëà ëîãè÷åñêîãî äèñêà
äëÿ read_sectors32, îòíîñèòåëüíî íà÷àëà äàííûõ
äëÿ read_sectors2)
cx = ÷èñëî ñåêòîðîâ (äîëæíî áûòü áîëüøå íóëÿ)
íà âûõîäå: es:bx óêàçûâàåò íà êîíåö áóôåðà, â êîòîðûé áûëè ïðî÷èòàíû äàííûå
ñòàðøèå ñëîâà 32-áèòíûõ ðåãèñòðîâ ìîãóò ðàçðóøèòüñÿ
0. Åñëè âûçûâàåòñÿ read_sectors2, îíà ïåðåâîäèò óêàçàííûé åé íîìåð ñåêòîðà
â íîìåð îòíîñèòåëüíî íà÷àëà ëîãè÷åñêîãî äèñêà, ïðèáàâëÿÿ íîìåð ñåêòîðà
íà÷àëà äàííûõ, õðàíÿùèéñÿ â ñòåêå êàê [bp-10].
1. Ïåðåâîäèò ñòàðòîâûé ñåêòîð (îòñ÷èòûâàåìûé îò íà÷àëà òîìà) â ñåêòîð íà
óñòðîéñòâå, ïðèáàâëÿÿ çíà÷åíèå ñîîòâåòñòâóþùåãî ïîëÿ èç BPB.
2.  öèêëå (øàãè 3-6) ÷èòàåò ñåêòîðû, ñëåäèò çà òåì, ÷òîáû íà êàæäîé èòåðàöèè
CHS-âåðñèÿ: âñå ÷èòàåìûå ñåêòîðû áûëè íà îäíîé äîðîæêå.
LBA-âåðñèÿ: ÷èñëî ÷èòàåìûõ ñåêòîðîâ íå ïðåâîñõîäèëî 7Fh (òðåáîâàíèå
ñïåöèôèêàöèè EDD BIOS).
CHS-âåðñèÿ:
3. Ïåðåâîäèò àáñîëþòíûé íîìåð ñåêòîðà â CHS-ñèñòåìó: ñåêòîð ðàññ÷èòûâàåòñÿ êàê
åäèíèöà ïëþñ îñòàòîê îò äåëåíèÿ àáñîëþòíîãî íîìåðà íà ÷èñëî ñåêòîðîâ
íà äîðîæêå; äîðîæêà ðàññ÷èòûâàåòñÿ êàê îñòàòîê îò äåëåíèÿ ÷àñòíîãî,
ïîëó÷åííîãî íà ïðåäûäóùåì øàãå, íà ÷èñëî äîðîæåê, à öèëèíäð - êàê
÷àñòíîå îò ýòîãî æå äåëåíèÿ. Åñëè ÷èñëî ñåêòîðîâ äëÿ ÷òåíèÿ áîëüøå,
÷åì ÷èñëî ñåêòîðîâ äî êîíöà äîðîæêè, óìåíüøàåò ÷èñëî ñåêòîðîâ äëÿ
÷òåíèÿ.
4. Ôîðìèðóåò äàííûå äëÿ âûçîâà int 13h (ah=2 - ÷òåíèå, al=÷èñëî ñåêòîðîâ,
dh=ãîëîâêà, (ìëàäøèå 6 áèò cl)=ñåêòîð,
(ñòàðøèå 2 áèòà cl è âåñü ch)=äîðîæêà, dl=äèñê, es:bx->áóôåð).
5. Âûçûâàåò BIOS. Åñëè BIOS ðàïîðòóåò îá îøèáêå, âûïîëíÿåò ñáðîñ äèñêà
è ïîâòîðÿåò ïîïûòêó ÷òåíèÿ, âñåãî äåëàåòñÿ íå áîëåå òð¸õ ïîïûòîê
(íåñêîëüêî ïîïûòîê íóæíî â ñëó÷àå äèñêåòû äëÿ ãàðàíòèè òîãî, ÷òî
ìîòîð ðàñêðóòèëñÿ). Åñëè âñå òðè ðàçà ïðîèñõîäèò îøèáêà ÷òåíèÿ,
ïåðåõîäèò íà êîä îáðàáîòêè îøèáîê ñ ñîîáùåíèåì "Read error".
6.  ñîîòâåòñòâèè ñ ÷èñëîì ïðî÷èòàííûõ íà òåêóùåé èòåðàöèè ñåêòîðîâ
êîððåêòèðóåò òåêóùèé ñåêòîð, ÷èñëî îñòàâøèõñÿ ñåêòîðîâ è óêàçàòåëü íà
áóôåð (â ïàðå es:bx êîððåêòèðóåòñÿ es). Åñëè âñ¸ ïðî÷èòàíî, çàêàí÷èâàåò
ðàáîòó, èíà÷å âîçâðàùàåòñÿ íà øàã 3.
LBA-âåðñèÿ:
3. Åñëè ÷èñëî ñåêòîðîâ äëÿ ÷òåíèÿ áîëüøå 7Fh, óìåíüøàåò åãî (äëÿ òåêóùåé
èòåðàöèè) äî 7Fh.
4. Ôîðìèðóåò â ñòåêå ïàêåò äëÿ int 13h (êëàä¸ò âñå íóæíûå äàííûå êîìàíäàìè
push, ïðè÷¸ì â îáðàòíîì ïîðÿäêå: ñòåê - ñòðóêòóðà LIFO, è äàííûå â
ñòåêå õðàíÿòñÿ â îáðàòíîì ïîðÿäêå ïî îòíîøåíèþ ê òîìó, êàê èõ òóäà
êëàëè).
5. Âûçûâàåò BIOS. Åñëè BIOS ðàïîðòóåò îá îøèáêå, ïåðåõîäèò íà êîä îáðàáîòêè
îøèáîê ñ ñîîáùåíèåì "Read error". Î÷èùàåò ñòåê îò ïàêåòà,
ñôîðìèðîâàííîãî íà ïðåäûäóùåì øàãå.
6.  ñîîòâåòñòâèè ñ ÷èñëîì ïðî÷èòàííûõ íà òåêóùåé èòåðàöèè ñåêòîðîâ
êîððåêòèðóåò òåêóùèé ñåêòîð, ÷èñëî îñòàâøèõñÿ ñåêòîðîâ è óêàçàòåëü íà
áóôåð (â ïàðå es:bx êîððåêòèðóåòñÿ es). Åñëè âñ¸ ïðî÷èòàíî, çàêàí÷èâàåò
ðàáîòó, èíà÷å âîçâðàùàåòñÿ íà øàã 3.
Ïðîöåäóðà ïîèñêà ýëåìåíòà â ïàïêå (lookup_in_dir):
íà âõîäå äîëæíî áûòü óñòàíîâëåíî:
ss:bp = 0:7C00
ds:si = óêàçàòåëü íà èìÿ ôàéëà â ôîðìàòå FAT (ñì. âûøå)
eax = íà÷àëüíûé êëàñòåð ïàïêè
bx = 0
íà âûõîäå: ôëàã CF îïðåäåëÿåò, óäàëîñü ëè íàéòè ôàéë; åñëè óäàëîñü, òî
CF ñáðîøåí è es:di óêàçûâàåò íà ýëåìåíò ïàïêè
 öèêëå ñ÷èòûâàåò êëàñòåðû ïàïêè è èùåò çàïðîøåííûé ýëåìåíò â ïðî÷èòàííûõ
äàííûõ. Äëÿ ÷òåíèÿ êëàñòåðà èñïîëüçóåò óæå îïèñàííóþ ïðîöåäóðó read_clusters,
äëÿ ïðîäâèæåíèÿ ïî öåïî÷êå êëàñòåðîâ - îïèñàííóþ äàëåå ïðîöåäóðó
get_next_clusters. Äàííûå ÷èòàþòñÿ â îáëàñòü ïàìÿòè, íà÷èíàþùóþñÿ ñ àäðåñà
8000:0000, ïðè ýòîì ïåðâûå 2000h áàéò èç äàííûõ ïàïêè (ìîæåò áûòü, ìåíüøå,
åñëè ÷òåíèå ïðåðâ¸òñÿ ðàíüøå) íå ïåðåêðûâàþòñÿ ïîñëåäóþùèìè ÷òåíèÿìè
(ýòî áóäåò èñïîëüçîâàíî ïîçäíåå, â ñèñòåìå êýøèðîâàíèÿ èç kordldr.f32).
Âûõîä îñóùåñòâëÿåòñÿ â ëþáîì èç ñëåäóþùèõ ñëó÷àåâ: íàéäåí çàïðîøåííûé ýëåìåíò;
êîí÷èëèñü ýëåìåíòû â ïàïêå (ïåðâûé áàéò î÷åðåäíîãî ýëåìåíòà íóëåâîé);
êîí÷èëèñü äàííûå ïàïêè â ñîîòâåòñòâèè ñ öåïî÷êîé êëàñòåðîâ èç FAT.
Ïðîöåäóðà âûâîäà íà ýêðàí ASCIIZ-ñòðîêè (out_string):
íà âõîäå: ds:si -> ñòðîêà
 öèêëå, ïîêà íå äîñòèãíóò çàâåðøàþùèé íîëü, âûçûâàåò ôóíêöèþ int 10h/ah=0Eh.
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Ðàáîòà âñïîìîãàòåëüíîãî çàãðóç÷èêà kordldr.f32:
1. Îïðåäåëÿåò, áûë ëè îí çàãðóæåí CHS- èëè LBA-âåðñèåé áóòñåêòîðà.
 çàâèñèìîñòè îò ýòîãî óñòàíàâëèâàåò ñìåùåíèÿ èñïîëüçóåìûõ ïðîöåäóð
áóòñåêòîðà. Êðèòåðèé ïðîâåðêè: â CHS-âåðñèè ïî àäðåñó err íàõîäèòñÿ
áàéò 0xE8 (ìàøèííàÿ êîìàíäà call), â LBA-âåðñèè ïî òîìó æå àäðåñó
íàõîäèòñÿ áàéò 0x14, à àäðåñ ïðîöåäóðû err äðóãîé.
2. Óçíà¸ò ðàçìåð ñâîáîäíîé áàçîâîé ïàìÿòè (ò.å. ñâîáîäíîãî íåïðåðûâíîãî êóñêà
àäðåñîâ ïàìÿòè, íà÷èíàþùåãîñÿ ñ 0) âûçîâîì int 12h.  ñîîòâåòñòâèè ñ
íèì âû÷èñëÿåò ÷èñëî ýëåìåíòîâ â êýøå ïàïîê. Õîòÿ áû äëÿ îäíîãî ýëåìåíòà
ìåñòî äîëæíî áûòü, îòñþäà îãðàíè÷åíèå â 592 Kb (94000h áàéò).
Çàìå÷àíèå: ýòîò ðàçìåð íå ìîæåò ïðåâîñõîäèòü 0A0000h áàéò è
íà ïðàêòèêå îêàçûâàåòñÿ íåìíîãî (íà 1-2 êèëîáàéòà) ìåíüøèì èç-çà
íàëè÷èÿ äîïîëíèòåëüíîé îáëàñòè äàííûõ BIOS "ââåðõó" áàçîâîé ïàìÿòè.
3. Èíèöèàëèçèðóåò êýøèðîâàíèå ïàïîê. Áóòñåêòîð óæå çàãðóçèë êàêóþ-òî ÷àñòü
äàííûõ êîðíåâîé ïàïêè; êîïèðóåò çàãðóæåííûå äàííûå â êýø è çàïîìèíàåò,
÷òî â êýøå åñòü êîðíåâàÿ ïàïêà.
4. Èíèöèàëèçèðóåò êýøèðîâàíèå FAT. Áóòñåêòîð èìååò äåëî ñ FAT â òîì è òîëüêî
òîì ñëó÷àå, êîãäà åìó ïðèõîäèòñÿ çàãðóæàòü äàííûå êîðíåâîé ïàïêè,
íå ïîìåñòèâøèåñÿ â îäèí êëàñòåð.  ýòîì ñëó÷àå â ïàìÿòè ïðèñóòñòâóåò
îäèí ñåêòîð FAT (åñëè áûëî íåñêîëüêî îáðàùåíèé - ïîñëåäíèé èç
èñïîëüçîâàííûõ).
5. Åñëè êëàñòåð ðàâåí ñåêòîðó, òî áóòñåêòîð çàãðóçèë òîëüêî ÷àñòü ôàéëà
kordldr.f32, è çàãðóç÷èê ïîäãðóæàåò âòîðóþ ñâîþ ÷àñòü, èñïîëüçóÿ
çíà÷åíèÿ ðåãèñòðîâ íà âõîäå â kordldr.f32.
6. Çàãðóæàåò âòîðè÷íûé çàãðóç÷èê kord/loader ïî àäðåñó 1000:0000. Åñëè ôàéë íå
íàéäåí, èëè îêàçàëñÿ ïàïêîé, èëè îêàçàëñÿ ñëèøêîì áîëüøèì, òî ïåðåõîäèò
íà êîä îáðàáîòêè îøèáîê èç áóòñåêòîðà ñ ñîîáùåíèåì
"Fatal error: cannot load the secondary loader".
Çàìå÷àíèå: íà ýòîì ýòàïå èìÿ ôàéëà óæå ìîæíî óêàçûâàòü âìåñòå ñ ïóò¸ì
è â ôîðìàòå ASCIIZ, õîòÿ ïîääåðæêè äëèííûõ èì¸í è íåàíãëèéñêèõ ñèìâîëîâ
ïî-ïðåæíåìó íåò.
7. Èçìåíÿåò êîä îáðàáîòêè îøèáîê áóòñåêòîðà íà ïåðåõîä íà ìåòêó hooked_err.
Ýòî íóæíî, ÷òîáû ïîñëåäóþùèå îáðàùåíèÿ ê êîäó áóòñåêòîðà â ñëó÷àå
îøèáîê ÷òåíèÿ íå âûâîäèë ñîîòâåòñòâóþùåå ñîîáùåíèå ñ ïîñëåäóþùåé
ïåðåçàãðóçêîé, à ðàïîðòîâàë îá îøèáêå ÷òåíèÿ, êîòîðóþ ìîãëî áû
êàê-íèáóäü îáðàáîòàòü ÿäðî.
8. Åñëè çàãðóçî÷íûé äèñê èìååò èäåíòèôèêàòîð ìåíüøå 0x80,
òî óñòàíàâëèâàåò al='f' ("floppy"), ah=èäåíòèôèêàòîð äèñêà,
èíà÷å al='h' ("hard"), ah=èäåíòèôèêàòîð äèñêà-0x80 (íîìåð äèñêà).
(Ãîâîðèòå, äèñêåòîê ñ FAT32 íå áûâàåò?  ÷¸ì-òî Âû ïðàâû... íî
óâåðåíû ëè Âû, ÷òî íåò çàãðóçî÷íûõ óñòðîéñòâ, ïîäîáíûõ äèñêåòàì,
íî áîëüøåãî ðàçìåðà, è äëÿ êîòîðûõ BIOS-èäåíòèôèêàòîð ìåíüøå 0x80?)
Óñòàíàâëèâàåò bx='32' (òèï ôàéëîâîé ñèñòåìû - FAT32).
Óñòàíàâëèâàåò si=ñìåùåíèå ôóíêöèè îáðàòíîãî âûçîâà. Ïîñêîëüêó â ýòîò
ìîìåíò ds=0, òî ds:si îáðàçóþò ïîëíûé àäðåñ.
9. Ïåðåäà¸ò óïðàâëåíèå ïî àäðåñó 1000:0000.
Ôóíêöèÿ îáðàòíîãî âûçîâà äëÿ âòîðè÷íîãî çàãðóç÷èêà:
ïðåäîñòàâëÿåò âîçìîæíîñòü ÷òåíèÿ ôàéëà.
Âõîä è âûõîä îïèñàíû â ñïåöèôèêàöèè íà çàãðóç÷èê.
1. Ñîõðàíÿåò ñòåê âûçûâàþùåãî êîäà è óñòàíàâëèâàåò ñâîé ñòåê:
ss:sp = 0:(7C00-10), bp=7C00: ïàðà ss:bp ïðè ðàáîòå ñ îñòàëüíûì
êîäîì äîëæíà óêàçûâàòü íà 0:7C00, à -10 áåð¸òñÿ îò òîãî, ÷òî
èíèöèàëèçèðóþùèé êîä áóòñåêòîðà óæå ïîìåñòèë â ñòåê 10 áàéò ïàðàìåòðîâ,
è îíè äîëæíû ñîõðàíÿòüñÿ â íåèçìåííîñòè. (Çíà÷åíèå [ebp-14],
"òåêóùèé ñåêòîð, íàõîäÿùèéñÿ â êýøå FAT", íå èñïîëüçóåòñÿ ïîñëå
èíèöèàëèçàöèè êýøèðîâàíèÿ â kordldr.f32.)
2. Ðàçáèðàåò ïåðåäàííûå ïàðàìåòðû è âûçûâàåò íóæíóþ èç âñïîìîãàòåëüíûõ
ïðîöåäóð (çàãðóçêè ôàéëà ëèáî ïðîäîëæåíèÿ çàãðóçêè ôàéëà).
3. Âîññòàíàâëèâàåò ñòåê âûçûâàþùåãî êîäà è âîçâðàùàåò óïðàâëåíèå.
Âñïîìîãàòåëüíûå ïðîöåäóðû kordldr.f32.
Ïðîöåäóðà ïîëó÷åíèÿ ñëåäóþùåãî êëàñòåðà â FAT (get_next_cluster):
1. Âû÷èñëÿåò íîìåð ñåêòîðà â FAT, â êîòîðîì íàõîäèòñÿ çàïðîøåííûé ýëåìåíò.
(Â ñåêòîðå 0x200 áàéò, êàæäûé âõîä çàíèìàåò 4 áàéòà.)
2. Ïðîâåðÿåò, åñòü ëè ñåêòîð â êýøå. Åñëè åñòü, ïðîïóñêàåò øàãè 3 è 4.
3. Åñëè íåò, òî â êýø íóæíî âñòàâèòü íîâûé ýëåìåíò. Åñëè êýø åù¸ íå çàïîëíåí,
âûäåëÿåò î÷åðåäíîé ýëåìåíò â êîíöå êýøà. Åñëè çàïîëíåí, óäàëÿåò
ñàìûé ñòàðûé ýëåìåíò (òîò, ê êîòîðîìó äîëüøå âñåãî íå áûëî îáðàùåíèé);
äëÿ òîãî, ÷òîáû îòñëåæèâàòü ïîðÿäîê ýëåìåíòîâ ïî âðåìåíè ïîñëåäíåãî
îáðàùåíèÿ, âñå (âûäåëåííûå) ýëåìåíòû êýøà ñâÿçàíû â äâóñâÿçíûé ñïèñîê,
â êîòîðîì ïåðâûì ýëåìåíòîì ÿâëÿåòñÿ ñàìûé ñòàðûé, à ññûëêè âïåð¸ä
óêàçûâàþò íà ñëåäóþùèé ïî âðåìåíè ïîñëåäíåãî îáðàùåíèÿ.
4. ×èòàåò ñîîòâåòñòâóþùèé ñåêòîð FAT ñ äèñêà.
5. Êîððåêòèðóåò ñïèñîê: òåêóùèé îáðàáàòûâàåìûé ýëåìåíò óäàëÿåòñÿ ñ òîé ïîçèöèè,
ãäå îí íàõîäèòñÿ, è äîáàâëÿåòñÿ â êîíåö. ( ñëó÷àå ñî ñâåæåäîáàâëåííûìè
â êýø ýëåìåíòàìè óäàëåíèÿ íå äåëàåòñÿ, ïîñêîëüêó èõ â ñïèñêå åù¸ íåò.)
6. Ñ÷èòûâàåò íóæíûé âõîä â FAT, ñáðàñûâàÿ ñòàðøèå 4 áèòà.
7. Ñðàâíèâàåò ïðî÷èòàííîå çíà÷åíèå ñ ïðåäåëîì: åñëè îíî ñòðîãî ìåíüøå
0x0FFFFFF7, òî îíî çàäà¸ò íîìåð ñëåäóþùåãî êëàñòåðà â öåïî÷êå;
â ïðîòèâíîì ñëó÷àå öåïî÷êà çàêîí÷èëàñü.
Ïðîöåäóðà çàãðóçêè ôàéëà (load_file):
1. Òåêóùàÿ ðàññìàòðèâàåìàÿ ïàïêà - êîðíåâàÿ. Â öèêëå âûïîëíÿåò øàãè 2-4.
2. Êîíâåðòèðóåò èìÿ òåêóùåãî ðàññìàòðèâàåìîãî êîìïîíåíòà èìåíè (êîìïîíåíòû
ðàçäåëÿþòñÿ ñèìâîëîì '/') â FAT-ôîðìàò 8+3. Åñëè ýòî íåâîçìîæíî
(áîëüøå 8 ñèìâîëîâ â èìåíè, áîëüøå 3 ñèìâîëîâ â ðàñøèðåíèè èëè
áîëüøå îäíîé òî÷êè), âîçâðàùàåòñÿ ñ îøèáêîé.
3. Èùåò ýëåìåíò ñ òàêèì èìåíåì â òåêóùåé ðàññìàòðèâàåìîé ïàïêå.
à) Ïðîâåðÿåò, åñòü ëè òàêàÿ ïàïêà â êýøå ïàïîê. (Èäåíòèôèêàöèÿ ïàïîê
îñóùåñòâëÿåòñÿ ïî íîìåðó íà÷àëüíîãî êëàñòåðà.) Åñëè òàêîé ïàïêè åù¸
íåò, äîáàâëÿåò å¸ â êýø; åñëè òîò ïåðåïîëíÿåòñÿ, âûêèäûâàåò ïàïêó,
ê êîòîðîé äîëüøå âñåãî íå áûëî îáðàùåíèé. (Äëÿ êàæäîãî ýëåìåíòà êýøà
õðàíèòñÿ ìåòêà îò 0 äî (ðàçìåð êýøà)-1, îïðåäåëÿþùàÿ åãî íîìåð ïðè
ñîðòèðîâêå ïî äàâíîñòè ïîñëåäíåãî îáðàùåíèÿ. Ïðè îáðàùåíèè ê êàêîìó-òî
ýëåìåíòó åãî ìåòêà ñòàíîâèòñÿ íóëåâîé, à òå ìåòêè, êîòîðûå ìåíüøå
ñòàðîãî çíà÷åíèÿ, óâåëè÷èâàþòñÿ íà åäèíèöó.)
á) Ïðîñìàòðèâàåò â ïîèñêàõ çàïðîøåííîãî èìåíè âñå ýëåìåíòû èç êýøà,
èñïîëüçóÿ ïðîöåäóðó èç áóòñåêòîðà. Åñëè îáíàðóæèâàåò èñêîìûé ýëåìåíò,
ïåðåõîäèò ê øàãó 4. Åñëè îáíàðóæèâàåò êîíåö ïàïêè, âîçâðàùàåòñÿ èç
ïðîöåäóðû ñ îøèáêîé.
â)  öèêëå ñ÷èòûâàåò ïàïêó ïîñåêòîðíî. Ïðè ýòîì ïðîïóñêàåò íà÷àëüíûå
ñåêòîðû, êîòîðûå óæå íàõîäÿòñÿ â êýøå è óæå áûëè ïðîñìîòðåíû. Êàæäûé
ïðî÷èòàííûé ñåêòîð êîïèðóåò â êýø, åñëè òàì åù¸ îñòà¸òñÿ ìåñòî,
è ïðîñìàòðèâàåò â í¸ì âñå ýëåìåíòû. Ðàáîòàåò, ïîêà íå ñëó÷èòñÿ îäíî èç
òð¸õ ñîáûòèé: íàéäåí èñêîìûé ýëåìåíò; êîí÷èëèñü êëàñòåðû (ñóäÿ ïî
öåïî÷êå êëàñòåðîâ â FAT); î÷åðåäíîé ýëåìåíò ïàïêè ñèãíàëèçèðóåò î êîíöå
(ïåðâûé áàéò íóëåâîé).  äâóõ ïîñëåäíèõ ñëó÷àÿõ âîçâðàùàåòñÿ ñ îøèáêîé.
4. Ïðîâåðÿåò òèï íàéäåííîãî ýëåìåíòà (ôàéë/ïàïêà): ïîñëåäíèé ýëåìåíò â
çàïðîøåííîì èìåíè äîëæåí áûòü ôàéëîì, âñå ïðîìåæóòî÷íûå - ïàïêàìè.
Åñëè òåêóùèé êîìïîíåíò èìåíè - ïðîìåæóòî÷íûé, ïðîäâèãàåò òåêóùóþ
ðàññìàòðèâàåìóþ ïàïêó è âîçâðàùàåòñÿ ê ïóíêòó 2.
5. Ïðîõîäèò ïî öåïî÷êå êëàñòåðîâ â FAT è ñ÷èòûâàåò âñå êëàñòåðû â óêàçàííûé
ïðè âûçîâå áóôåð ïîñëåäîâàòåëüíûìè âûçîâàìè ôóíêöèè áóòñåêòîðà;
ïðè ýòîì åñëè íåñêîëüêî êëàñòåðîâ ôàéëà ðàñïîëîæåíû íà äèñêå
ïîñëåäîâàòåëüíî, òî èõ ÷òåíèå îáúåäèíÿåòñÿ â îäíó îïåðàöèþ.
Ñëåäèò çà òåì, ÷òîáû íå ïðåâûñèòü óêàçàííûé ïðè âûçîâå ïðîöåäóðû
ëèìèò ÷èñëà ñåêòîðîâ äëÿ ÷òåíèÿ.
Ïðîöåäóðà ïðîäîëæåíèÿ çàãðóçêè ôàéëà (continue_load_file): âñòðîåíà
âíóòðü øàãà 5 load_file; çàãðóæàåò â ðåãèñòðû íóæíûå çíà÷åíèÿ (ðàíåå
ñîõðàí¸ííûå èç load_file) è ïðîäîëæàåò øàã 5.