Re: [colorforth] Hello - and where to begin?
- Subject: Re: [colorforth] Hello - and where to begin?
- From: "Ray St. Marie" <ray.stmarie@xxxxxxxxx>
- Date: Mon, 10 Mar 2008 16:23:38 -0600
On Mon, Mar 10, 2008 at 2:58 AM, Nick Maroudas
<alice@xxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> Nick here: Dear Ray,
>
> Thanks for your interest, below are further details;
> rather long, but might be suitable for one of John
> Drake's tutorials.
>
> Caritas,
>
> NickM
>
> ***************************
>
> Timing and Music - Tutorial
>
> Howerd Oakford's CFDOS4 has three blocks which
> illustrate
> the use of PC timers. You can make a boot floppy from
> DOS
> by following the instructions on Howerd's website; or
> just copy his bootable image cfdos4.blk with Linux,
> dd if=cfdos4.blk of=/dev/fd0
>
> The PC has 3 timers. The newest and fastest is the 64
> bit
> RDTSC (Time Stamp Counter) which ticks at CPU rate, ns,
>
> and loads the time, in clock ticks, onto EAX lo & EDX
> hi.
> CF has a macro word "time" which calls RDTSC, with lo 32
>
> bits on stack, EAX. The first thing Howerd does is to
> bring
> this macro word "time" into his forth dictionary, block
> 20,
>
> forth : time time ; --u
>
> I find it useful to stack the higher 32 bits as well.
> This can
> be called by the the forth word "a", which stacks EDX.
> So my version of "time" is "clk",
>
> ( still in forth) : clk time a ; --ulo uhi
>
> Block 28 uses the fast 64 bit PC timer to make delays in
>
> msec "ms" and "secs". Howard uses the PC's second timer
>
> for calibration. Real Time Clock (RTC) at port 70h,
> ticks
> hi and lo every second. Howerd defines a variable
> "khz"
> to store the number of PC CPU ticks in one sec, divided
> by
> 1000 to bring it to ms. (I find "1ms" a useful memnonic
> for
> "khz"). The word "cal" ought to put your CPU's clock
> rate
> into the variable "khz".
>
> : cal hi lo time invert ( howerd's word to change
> sign)
> hi lo time + ( time diff, no of clks
> in 1 sec)
> 1000 / khz ! ; ( ditto, in 1 msec)
>
> But if the CPU is faster than 1GHz, a one sec
> calibration
> period will be too long, because the lower 32 bit
> register
> of the RDTS counter will overflow. Hence I call the
> higher
> 32 bit register as well, and scale the 2 numbers
> appropriately
> before adding them to make a 32 bit time scale.
>
> : clk time 10 shr a 31 and 22 shl + ; --u (
> hi+lo, scaled)
>
> : cal clk invert clk + 1000 / khz ! ;
>
> Having calibrated his time interval (for length of a
> note)
> Howerd then uses the PC's 3rd timer to set the
> frequency.
> The Programmable Interrupt Timers (PIT) tick microsec.
> See Mark Feldman's tutorial "Controlling the PC speaker"
>
> on the popular Australian website, "JollySWAGman"
>
> http://www.bsdg.org/SWAG/SOUND/0107.PAS.html
>
> The PC speaker is tied to the NMI status port 61h.
> There
> are caveats about writing to some other bits (see Intel
> doc
> ICH7) but, essentially, bit 0 will activate the speaker
> and
> bit 1 will tie it to the pulses from PIT 2. This timer
> is
> selected by writing a byte to port 43, and its
> oscillatory
> half-period is entered as hibyte lobyte-- to port 42h.
>
> Therefor Howerd introduces the macro word "swapbytes"
> and defines a forth word to "split" 16bits into 2 bytes,
>
> before moving on to make music.
>
> Block 68 is straightforward, and rather neat. It save a
> bit
> of repetitive naming by use of the CF facility where one
> word
> can elide into its successor if its ";" is omited.
>
> : tn ( this is the note length t, scaled to msec)
>
> : hz ( this is the PIT rate 1,193,000 ticks per sec,
> divided
> by the freq in Hz - actually, this is the
> pulse period)
>
> : tone ( the period is split and written to PIT2,
> which sets
> up oscillation freq; PIT2 output is tied
> to speaker
> by writing a 3 to port 61, then it is
> untied - after
> t msec - by replacing the 3 with a 1; this
> silences
> the tone, plus 20 ms delay before next
> tone) ;
>
>
> *************************
>
>
> ---------------------------------------------------------------------
> To unsubscribe, e-mail: colorforth-unsubscribe@xxxxxxxxxxxxxxxxxx
> For additional commands, e-mail: colorforth-help@xxxxxxxxxxxxxxxxxx
> Main web page - http://www.colorforth.com
>
>
Thank you for this, Nick!
Thank you, also, for the link to SWAG. It's been a long time since
I've been to that site. Great resource. Soon as I get done catching up
there, I'm going to load "Howerd" ( what I call any of his sources,
normally the very last otherwise I tend to add a digit as in Howerd2
or HowO-4 even ) and follow along with your tutorial here.
I've read Howerd's code in the past but unless you have used the
timers or have some frame of ref, the code is pretty but thats not
enough, sometimes. :-)
So again, Thanks!
Ray
--
Raymond St. Marie ii,
---------------------------------------------------------------------
To unsubscribe, e-mail: colorforth-unsubscribe@xxxxxxxxxxxxxxxxxx
For additional commands, e-mail: colorforth-help@xxxxxxxxxxxxxxxxxx
Main web page - http://www.colorforth.com
