Writing Drivers

NWCCTV · 2013-01-21 17:12

Where would be a good place to start if I want to learn how to write drivers for various hardware devices and what piece of hardware would be an easy item to start with?

kwinn · 2013-01-21 17:25

Drivers for the Propeller, Windows, or some other CPU?

If it's for the propeller I would suggest starting with some simple hardware like the '595 chip.

NWCCTV · 2013-01-21 17:34

I was just pondering drivers in general. I think the propeller would be a good start. What is the 595 chip and where would I start?

Duane C. Johnson · 2013-01-21 18:23

Wow, what a coincidence!!!

I have been writing a driver for the 74HC595, 74HC4094, and 74HC4021 shift registers.
The 595 and 4094 are serial in to 8 bit parallel out, and the 4021 is 8 bit parallel in to serial out.

I'm adding a pair of instructions to Mike Greens FemtoBasic. These code snippets are written in spin:

204: ' SROUT [<expr>] = <expr>
                 ' SROUT [<Pin#>] = <Value>
               a := getAddress(dot)
               outa[a..a+3] := %0000
               dira[a..a+3] := %1110
               b := specialExpr
               repeat 32
                  outa[a+2] := b & 1             ' Send   a    Bit  To The Registers
                  b <-= 1                        ' Rotate Left Bits In The Variable
                  outa[a]~~                      ' Shift  Left Bits In The Registers
                  outa[a]~
               outa[a+1]~~                       ' Strobe The Output Registers
               outa[a+1]~

205: ' SRIN [ <expr> ]
         t := getAddress(dot)
         outa[t..t+3] := %0000
         dira[t..t+3] := %1110
         i := 0
            outa[t+1]~~      ' Strobe The Registers
            outa[t+1]~
            repeat 32
               i += ina[t+3] ' Put    a     Bit  In The Variable
               i <-= 1       ' Rotate Left  Bits In The Variable
               outa[t]~~     ' Shift  Left  Bits In The Registers
               outa[t]~ 
            i += ina[t+3]    ' Put Last Bit      In The Variable
         return i

This simple example expects the there are 4 chips strung in series for a total of 32 bits;
Any combination of output or input devices can be used.
This consumes 4 Prop pins which must be in sequence.
1 = Shift Clock
1+1 = Register Clock
1+2 = Serial Bits Out
1+3 = Serial Bits In

Ok these examples are specific to FemtoBasic but the concept is sound.

Enhancements:
Allow from 1 to 4 or more chips on a set of 4 Prop pins.

I am looking for a code snippet that will be the equivalent of a "ROL", Rotate Left, spin instruction that can rotate 2 to 31 bits instead of the standard 32 bits.

Duane J

NWCCTV · 2013-01-21 20:31

OK, You lost me at Wow!!!!

frank freedman · 2013-01-21 20:57

Pick something in the OBEX that is not too complex and pick it apart, check out some stuff JonnyMac has posted both for methods and style.

kwinn · 2013-01-21 21:50

NWCCTV wrote: »

OK, You lost me at Wow!!!!

It really is a simple chip to start with. Only needs 3 signals to start with (plus power and ground of course), SER, SCK, and RCK. Download the data sheet and buy a '595 locally along with 8 hi efficiency leds and 8 180 to 220 ohm resistors. Connect the leds and resistors to the output pins of the '595, its SER, SCK, AND RCK pins to 2 free pins on the micro, ground the /G pin, put a pullup on the SRCLR pin and you are off to the races. I can post a block diagram if you want.

Writing Drivers

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