Cteni portu ISA

Slavomir Skopalik skopalik
Středa Březen 17 11:49:11 CET 2004


Ono taky zalezi na HW, co je na te ISE, zkuste cist napriklad z portu casovace (integrovane priferie),
potom z portu ISA video karty a pak s pararelniho portu (o ten Vam asi jde).
jinak jsem zkousel EPP a dostal jsem se na cca 0.5 - 1 MB/sec podle delky kabelu
a schopnostem druheho konce (zarizeni). On totiz EPP (a asi i ECP) port ceka dokud
zarizeni nepotvrdi prijem (nebo na time out).

	Slaek

> 
> Nevite nekdo, proc nedokazu cist z portu na ISA smernici rychleji nez 500kHz
> ?
> Stejne je to z Windows i z DOSu (nabootovano do DOSu), na dvou ruznych
> pocitacich (Pentium 100MHz a Duron 700MHz).
> Podle nize uvedeneho by to melo jit rychlosti 2,7MHz (v 16-bit. rezimu - ten
> moje karta pouziva).
> Nameril jsem v 16-ti bitovem rezimu asi 500kHz a v 8-mi bitovem asi 330kHz.
> Pouzivam nasledujici rutinu a merim cas, za jaky se to provede:
>         mov dx,PortNaISA
>         mov bx,1000
>         cli
> sm1: mov cx,10000
> sm2: in ax,dx
>         loop sm2
>         dec bx
>         jnz sm1
>         sti
> Netusite nekdo, co delam spatne ? Jak to zrychlit ?
> Jirka Netopil
> 
> Speed:
> Q: How can Parallel Port ISA card support quoted rates of data transfer in
> excess of 1MB/sec ? As far a I know every in/out command for an ISA bus
> address takes at least 1 microsecond to perform REGARDLESS of processor
> speed ?
> A: A simple parallel-port read or write does take one ISA-bus cycle, and on
> most systems, the bus speed is around 1.3 Mhz, so one cycle is a little
> under 1 microsecond. A complete data transfer on the original parallel port
> usually takes at least 4 cycles, however: check the Busy status, write the
> data, bring Strobe low, then high. On ports that support EPP and ECP modes,
> in these modes the port hardware does the handshake, and a complete transfer
> can take place in 1 bus cycle.
> There are at least two ways of getting faster data transfers: Some ports
> support a "fast mode" that uses the ISA bus's NOWS (no wait state) signal to
> cause the CPU to skip 3 wait states. This mode is twice as fast, or around
> 2.7 Mhz. ECPs also include hardware support for data decompressing (&
> sometimes compressing, though that's often left for software), so the
> effective rate of data transmission can be much faster than the number of
> bytes written or read per second. Also, ECPs may be able to transfer data
> between the host's and peripheral's ECP buffers at rates greater than 1 Mhz,
> though the buffers are typically just 8 bytes.
> 






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