Peri hardware (was Re: Hi)

[Alexios Chouchoulas]

On Wed, 4 Feb 1998, Tasos Bassoukos wrote:

> Se merika systhmata (merika RISC kai o palios kalos 68000) yparxei bus
> error me thn morfh tou la8os alignment, px. an pas na diavaseis/grapseis
> 2/4-byte word se perrith (odd , (x&1)==1) diay8ynsh.
> Se megalytera 680x0 to dior8osan ayto to feature :(

  Genikws einai xrhsimh dynatothta na mporeis na spas ta alignment rules
an to exeis apolyth anagkh. Arkei oi poines apodoshs na einai poly faneres
pantou sthn tekmhriwsh...

  Ti ennoeis *PALIOS* kalos 68000? Afth th stigmh exw s'afto to dwmatio enan
68000 (nai, to megalo platy xthnos sto DIL64 paketo) mesa s'ena X Terminal
kai dyo (syntoma treis) 68020 (enan/dyo sta 16.67 MHz, enan sta 25). Malista
sthn defterh periptwsh (Sun 3/160 me mpolikes kartes CPU gia antallaktika),
yparxei ston SCSI controller (3rd party) enas Intel 80186 ws I/O CPU. Etsi
prepei, h swsth ierarxia. :-)


> > antistoixo exception me to SIGSEGV einai to GPF [2] kai einai exception 13
> > [3]. SIGBUS den exoume stous i386). Oi platformes allazoun, alla orismena
> > pragmata menoun.
> 
> Ti, den mporeis na prokalesei mia e3wterikh syskeyh/controller ena bus
> error ? Hm... tou x86 tou leipoun perissotera pragmata ap' oti nomiza
> ... :-)

  Ap'oti kserw den mporei. Ta exceptions sthn x86 arxitektonikh einai
software interrupts, oxi hardware (h mallon einai hardware, alla
prokalountai mono eswterika apo ton epeksergasth kai katalambanoun ta
interrupts 0x10 ws 0x18 h 0x20(?)). Tha mporouses dynhtika na
xrhsimopoihseis ena apo ta dyo (!) interrupt lines tou epeksergasth (h mhpws
exei panw apo IRQ kai NMI twra?) gia na prokaleseis device exceptions (oxi
device interrupts -- px NMI gia exceptions, IRQ gia interrupts). Alla sthn
arxitektonikh twn IBM 5150 kai symbatwn, afto den exei ylopoiithei (na
xairomaste pou eixan ylopoiithei kai ta 8 multiplexed interrupts pou eixe to
5150, kai 16 pou exoume emeis oi foberoi sygxronoi PCades).

  To interrupt handling sta 5150 symbata (tromara mas) einai to ena kludge
panw apo to allo: CPU xwris arketa hardware interrupt lines, enas PIC gia
IRQ multiplexing, meta allos enas cascaded PIC gia parapanw interrupts
[opote kai emfanizetai ekeinh h blakeia me ta IRQ2/IRQ9] klp. Akoma, to
swthrio etos 1998 (mX) doulevoume me dyo hardware emulated, cascaded 8257
Programmable Interrupt Controllers).


> > [1] Ta PDP-11 kai oi apogonoi tous kanoun memory-mapped I/O.
> 
> Opws ola ta swsta systhmata :)

  E, afto paizetai. Opws to 50% twn systhmatwn. :-)  Metaksy mas, ektimw thn
dynatothta na exei kaneis aneksarthto I/O. Krataei th mnhmh gia pio swsta
pragmata (opws mnhmh), alla einai kai poly pio periploko na xtiseis buses
gia tetoies arxitektonikes. Apo thn allh, armozei pio poly se unixokouta to
MM I/O, giati dinei ena hardware abstraction se epipedo hardwarei (oles oi
syskeves leitourgoun me ena aplo tropo, me I/O sth mnhmh -- aplopoioume kai
to instruction set). Den einai tyxaio pou oloi oi RISC kanoun MM I/O.


> > [2] General Protection Fault
> 
> Alh8eia, pote den katalava akrivws ti shmainei to 'General'. Yparxei se
> antidiastolh me kapoio 'Specific Protection Fault' ?

  Nai, peripou... Ta exceptions tou x86 exoun mia apistefta eksypnh analogia
xtyphmatwn. GPF barame mia fora ana trilepto (katw apo Luse95). Floating
Point Faults fevgoun pote pote. Spania pairneis kai kanena Stack Fault. Ta
alla den ta exw dei pote mou, den kserw ti kanoun, poios eiste eseis kyrie,
klp. E, profanws den einai "Specific Protection Fault" to GPF. Pws na einai,
afou kalyptei to 95% twn lathwn pou mporoun na ginoun ston epeksergasth,
mazi me Bus faults, alignment errors klp klp klp pragmata pou tha'prepe
genika na einai xwria.

  Toulaxiston yparxei ENA elpidoforo pragma gia tis arxitektonikes ths
Intel. Twra pou agorase ton Alpha apo thn (makaritisa se ligo) Digital, h
epomenh platforma ths Intel mporei na einai safws kalyterh ap'oti exei
paragei monh ths edw kai, xm, 23 xronia.


> > [4] Alithinh core memory. Siderenioi daktylioi me tria kalwdia na pernane
> >     apo to kentro tous. Kathe daktylios = 1 bit. As mhn syzhthsoume gia
> >     access times, ok?
> 
> Na mantepsw: tis metras kalytera me hliako roloi h me radioxronologhseis

  As poume oti otan ena block mhnhms phrynwn exei designation "-95" h
"-950", *DEN* ennoei 950 nsec.

  Bebaia to core memory exei merika megala kala. To basikotero einai oti
einai non-volatile. Kleineis to PDP-8 sou oso doulevei. To anabeis meta apo
kana mhna otan to thymitheis kai synexizei apo kei pou eixe stamathsei
akribws. Malista, h DEC, gia na mhn dwsei meionekthmata sthn solid-state
mnhmh otan prwtoebgale tetoies kartes gia ta PDP, tous ebale kai battery
back-up, opote oles ths oi kartes htan non-volatile. Ypothetw oti oi
xeiristes tha tromazan tis prwtes fores otan anakalyptan oti h kainouria,
omorfh, grhgorh MOS RAM tous den kratouse ta dedomena ths "after dark". :-)

  BTW, to core memory einai h monh mnhmh pou pairnei xrono t gia grapsimo
kai xrono 2t gia diabasma, oxi o antitheto (otan diabazeis xanontai ta
dedomena kai o memory controller kanei allo ena kyklo gia na ta
ksanagrapsei).

  Ola afta einai teleiws asxeta me to Linux, fysika, mia kai den trexei se
PDP (h se Sun 3/160).

  A.

-------------------------- ,o88,o888o,,o888o. --------------------------------
Alexios Chouchoulas         '88    ,88'   ,88'   http://www.vennea.demon.co.uk 
The Unpronounceable One    ,o88oooo88ooooo88oo,     alexios at vennea.demon.co.uk

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