podule.html

关于ARM汇编的非常好的教程

    ENDIF
  ENDIF
NEXT

REM Once we know our base address, we can set up some offsets.
REM The down conversion changes our podule access methods.
visionheader% = visionbase% - &180000 : REM Base, slow access
visionctrl% = visionheader% + &102800 : REM Control, fast access
visiondata% = visionheader% + &103800 : REM Data, fast access
visionstat% = visionheader% + &100080 : REM Status, fast access
visionrst%  = visionheader% + &2000   : REM Reset, slow access

REM Code to reset, check, and fetch image removed
REM not necessary for this example

END

DEFPROCassemble
  DIM code% 76
  FOR loop% = 0 TO 2 STEP 2
    P% = code%
    [ OPT     loop%

      \ On entry, R1 = base address
      \ On exit,  R2 = 1 if Vision, else 0
    .find_podule%
      ; Stash R14 and enter SVC mode.
      STMFD   R13!, {R14}
      SWI     "OS_EnterOS"

      ; Set flag to TRUE. If a test fails, flag will be FALSified. <g>
      MOV     R0, #1

      ; Is +12 &AF?
      LDRB    R2, [R1, #12]
      CMP     R2, #&AF
      MOVNE   R0, #0

      ; Is +16 &00?
      LDRB    R2, [R1, #16]
      CMP     R2, #&00
      MOVNE   R0, #0

      ; Is +20 &2D?
      LDRB    R2, [R1, #20]
      CMP     R2, #&2D
      MOVNE   R0, #0

      ; Is +24 &00?
      LDRB    R2, [R1, #24]
      CMP     R2, #&00
      MOVNE   R0, #0

      TEQP    PC, #0
      MOV     R0, R0

      LDMFD   R13!, {PC}
    ]
  NEXT
ENDPROC
</pre>

For an interesting look at the Vision digitiser in use, you can either see the Willow (Alyson
Hannigan) area of my website at
<a href="http://www.heyrick.co.uk/willow/">http://www.heyrick.co.uk/willow/</a> <font color = "red" size = "-1">[EXTERNAL LINK]</font>, or, maybe even
more interesting, a person has taken pictures of the moon with a video camera and digitised them
with a monochrome Vision, at <a href="http://www.newtownbreda.demon.co.uk/ruadhan/asmoon.html">http://www.newtownbreda.demon.co.uk/ruadhan/asmoon.html</a> <font color = "red" size = "-1">[EXTERNAL LINK]</font>.
<p>&nbsp;<p>


<h2>SMC37C665</h2>

<img src = "../images/assembler/37c665.jpeg" width=209 height=314 alt="JPEG; 16K" align="right" border="0" vspace="2">

The name may not make much sense to you, but if you are using a RiscPC then it is a very
important name. The 37C665 (pictured) is the device that handles your parallel port, serial port,
floppy disc, IDE bus...<br>
The original Archimedes machines used seperate integrated circuits for these facilities; the A310
having no harddisc as standard, the A3000 having no harddisc or serial port as standard.<br>
The A5000 / A4 machines were the first to utilise an off-the-shelf 'combo chip' for the standard
interfacing. The chip was the 82C710.<br>
The RiscPC decided to alter the combo chip to be a 37C665. My personal suspicion is that the
37C665 was preferred because it features on-chip protection circuitry so your serial and parallel
ports can be wired without additional filters. It is clean, it is simple. Both devices conform
to the ISA specification for memory locations in a PC (ie, where COM1 and LPT1 live), so both
will be memory-mapped kinda similar.<br>
What I don't get, for what it's worth, is why Acorn didn't bother to fit a second serial port?
If you've ever opened your RiscPC (who hasn't?), you'll notice the serial hardware is really
quite simple (see the serial port, see the little chip just below it - that's the 37C665). The
37C665 supports TWO serial ports, right there in the hardware. Or maybe 1 serial port and one
MIDI port (differing configurations). It's just a shame Acorn didn't take advantage of this!<br>
Later machines (Mico, RiscStation, Bush internet box, etc) appear to use a 37C669 which allows
for the I/O addresses to be altered in software.
<p>

In order to read the configuration of the 37C665, we need to write &amp;55 (85) to port &amp;3F0.
However, we don't yet know where in memory the device is located. There are two ways to determine
the location of the device:
<ul>
  <li> The easy way - ask somebody that knows. Theo Markettos told me to poke around
       &amp;03010000+(ISAaddress&lt;&lt;2) for the devices.<br>
       (thanks Theo!)
       <br>&nbsp;<br>

  <li> We've already seen the &quot;Parallel_HardwareAddress&quot; SWI. This returns the value
       <code>&amp;30109E0</code>.<br>
       We know (from the 37C665 datasheet or just know-how about PCs) that LPT1 is located at
       &amp;278 (remember - the 37C665 is an ISA bus chip, so that junk that AMIBIOS shows you
       at boot time is suddenly looking like it might be useful!).<br>
       Because the bottom two bits are zero in the hardware access (ie, word addressing) then we
       need to shift the LPT1 address left twice. This gives us <code>&amp;278 &lt;&lt; 2</code>
       which is <code>&amp;9E0</code>.<br>
       Subtract &amp;9E0 from the parallel address, we have our device based at &amp;3010000.
</ul>
<p>

So, port &amp;3F0 (which becomes &amp;FC0 when shifted) is where we write &amp;55 to set the
device into configuration mode. Two consecutive writes must be made, so it is worth switching
off interrupts.<br>
<b><i>This will only work on the RiscPC, and you <u>MUST</u> release yourself from configuration
mode before attempting to use your computer. It goes without saying that you ONLY read the
configuration registers, never write to them!</i></b>
<p>

Once we are in configuration mode, we write a register number (0-15) to &amp;3F0 and we can then
read the value of that register from &amp;3F1. It is simple to whizz through the registers,
dumping the contents to memory as we go.
<p>

To leave configuration mode, we write &amp;AA to &amp;3F0. This must be done or your computer's
I/O will just cease to function.
<p>

This code will <i>ONLY</i> work on the 37C665 fitted into the RiscPC. It is worth noting that the
37C666 (basically a 665 but uses hardware links to configure it, the sort of thing you'd find on
a cheap ISA combo-card) uses the magic value &amp;66 to enter configuration mode. If your machine
has a different I/O chip, like the RiscStation or A7000, you might like to try a different
machine value if &amp;55 doesn't work. Maybe &amp;99? This is speculation though, as my data
sheet doesn't cover the 37C669. Please email me if you discover a sequence that works.
<p>

<i>November 2001:<br>
A friend has got a Bush Internet box for me, Toy-R-Us are apparently selling them for TWENTY
POUNDS!!! Anyway, when I've paid him and taken delivery of it, I'll play around, see what is
inside it. If you have a Bush internet box, then you might like to know that it should be
possible to boot the thing into the command line (or BASIC?) by holding down the Shift key while
booting.</i>
<p>&nbsp;<p>


This takes place in SVC mode, with interrupts disabled. The code is pretty basic really. I rather
suspect that the final <code>TEQP</code> could be combined into the <code>MOVS PC, R14</code> to
restore the flags <i>and</i> interrupt state. But doing it this way makes sure... The code is not
32bit compliant.
<p>

<pre>ON ERROR PRINT REPORT$+&quot; at line &quot;+STR$(ERL/10) : END

DIM code% 128

FOR l% = 0 TO 2 STEP 2
  P% = code%
  [ OPT     l%

    STR     R14, [R13, #-4]!

    SWI     &quot;OS_EnterOS&quot;
    TEQP    PC, #&amp;0C000003     ; interrupts disabled

    LDR     R0, base_address
    MOV     R1, #&amp;55
    STRB    R1, [R0, #&amp;FC0]    ; port &amp;3F0
    STRB    R1, [R0, #&amp;FC0]
    ; Now in 37C665 software configuration mode

    ADR     R2, registers      ; Where to store registers
    MOV     R3, #0             ; Register number (&amp; offset)

  .read_loop
    ; Write desired register number to address &amp;3F0
    STRB    R3, [R0, #&amp;FC0]
    ; Now read register contents from address &amp;3F1
    LDRB    R1, [R0, #&amp;FC4]
    ; Store it in our register block
    STRB    R1, [R2, R3]

    ADD     R3, R3, #1
    CMP     R3, #16
    BLT     read_loop

    MOV     R1, #&amp;AA
    STRB    R1, [R0, #&amp;FC0]
    ; Now out of software configuration mode

    TEQP    PC, #&amp;08000000     ; interrupts enabled, USR mode
    MOV     R0, R0

    LDR     R14, [R13], #4
    MOVS    PC, R14


  .base_address
    EQUD    &amp;03010000

  .registers
    EQUD    0
    EQUD    0
    EQUD    0
    EQUD    0
  ]
NEXT

PRINT &quot;Examining multi-I/O chip configuration...&quot;;
CALL code%
PRINT &quot;done.&quot;''

PRINT &quot;Device identification &quot;;
CASE registers?13 OF
  WHEN &amp;65 : PRINT &quot;FDC37C665GT&quot;;
  WHEN &amp;66 : PRINT &quot;FDC37C666GT&quot;; : REM Different magic value, so should not happen!
OTHERWISE  : PRINT &quot;Error! Device ID &quot;+STR$~(registers?13)+&quot; unrecognised!&quot; : END
ENDCASE
PRINT &quot;, revision &quot;+STR$(registers?14)

END
</pre>
<p>

Briefly, the registers are:
<ol start = "0">
  <li> IDE status, floppy status, oscillator status
  <li> Parallel status, COM 3 &amp; 4 status
  <li> Primary and secondary serial status
  <li> Floppy mode
  <li> Parallel mode / prim/sec serial clock (for MIDI)
  <li> IDE mode, floppy
  <li> Floppy drive types
  <li> Floppy boot / media ID
  <li> ADRx address decoder (lower eight bits)
  <li> ADRx address decoder (upper three bits)
  <li> ECP FIFO threshold
  <li> (reserved)
  <li> (reserved)
  <li> Device ID (should be &amp;65)
  <li> Device revision (should be &amp;02)
  <li> (reserved - sets up test modes)
</ol>

You'll need the <a href="http://www.smsc.com/main/datasheets/37c665gt.pdf">SMC37C665 device
datasheet</a> <font color = "red" size = "-1">[EXTERNAL LINK]</font> if you care to fiddle around with the registers, find out what is where...<br>
<p>&nbsp;<p>


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<address>Copyright &copy; 2001 Richard Murray</address>
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