[colorforth] rtl8139b driver

[Mark Slicker <maslicke@xxxxxxxxxxx>]

Please take a look a the following code which comes from the colorForth 
rtl8139b network driver:

: tx ( -b ) [ $2000 block 4 * ] ;
: rx ( -b ) [ tx 1536 + ] ; variable ds 1 variable fr 42
: n ( -a ) [ ds ] @ [ $10 r ] + ;
: send ( an ) [ fr ] @ [ tx ] + swap dup [ fr ] +! move ;
: first ( an ) n @ $2000 and drop if [ ds ] dup @ 1 + 3 and swap ! 0 [ fr 
] ! send ; then first ;
: last ( an ) send tx [ ds ] @ [ $20 r ] + ! [ fr ] @ 60 max n ! ;

If you are not familer with this code, the word 'r' returns the address of 
a register on the rtl8139b given a register offset. The word 'n' returns 
the address of one of four "transmit status register"s. Please see the rtl 
documentation for more information on these registers[1].

'first' checks whether the DMA operation on the previous packet is 
completed with the sequence "n @ 2000 and drop". If this true the transmit 
buffer is free for assembling the next packet, otherwise 'first' is 
repeated.

It seems the way this driver is programmed, all four "transmit status 
register"s are not needed and actually one would suffice. I believe this 
is true because the next packet must wait for the previous packet to be 
transfered by the rtl8139b, therefore the previous "transmit status 
register" can be reused for the next packet.

From my reading of the rtl8139b documentation the following code would 
be equivalent:

: tx ( -b ) [ $2000 block 4 * ] ;
: rx ( -b ) [ tx 1536 + ] ; variable fr 42
: n ( -a ) [ $10 r ] ;
: send ( an ) [ fr ] @ [ tx ] + swap dup [ fr ] +! move ;
: first ( an ) n @ $2000 and drop if 0 [ fr ] ! send ; then first ;
: last ( an ) send tx [ $20 r ] ! [ fr ] @ 60 max n ! ;

The difference is in the elimination of the 'ds' variable and related 
code. I don't have an rtl8139b, so I would be interested if anyone using 
this code could test my modifcation. Part of my interest in this code is 
documenting the existing colorForth networking and extending its 
capability.

Mark

[1] http://personalwebs.oakland.edu/~maslicke/colorforth/networking/rt8139b.pdf

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