BushSTB serial0 ppp link <-> unix success

[Matt Evans]

Dear Ladies & Gents,

Further to our last discussion on the first (unused) serial port on
the Bush STB, I have moved forwards a little.

I managed to get the STB talking PPP at 115200bps to my BSD box, under
RISC OS/NC OS, such that the desktop/NCFresco work transparently over
the serial link as if it were a modem link.

*phew*

The problem last time was that devices:$.Serial1 exists and you can
open it, but it does nothing.  On closer examination (read: "getting
stung in the arse trying to find why serial IRQs in linux wouldn't
work) it is an IRQ problem.  The SMSC 37C669 SuperIO chip goes through
a configuration mode when the OS boots, and is told what IO addresses
and IRQs it should respond to & generate.  The NCOS sets up the
SuperIO chip so that UART0 IRQs go out of pin IRQ_D, and UART1 IRQs go
through IRQ_C.  But, IRQ_D isn't connected to anything (!) whereas
IRQ_C goes through an inverter(ish) to nIRQ6 of the 7500FE... as the
serial IRQ that works.

The solution's simple - you reconfigure the SuperIO so that it
generates IRQs from both UARTs sharing the same pin IRQ_C.

The following BASIC program performs this (it's a little longer than
needs be, I can't remember where the config registers are; they aren't
arbitrary on the STB).

-------8<------8<------ izipfs:$.SIO --------8<----------

   10 REM>SIO
   15 REM Re-configure the STB's superio so both serial ports share 1 IRQ
   17 REM (*not* as the NCOS ROM configures it!)  8/8/02 Matt Evans
   20 DIM c% 2048
   30 FOR p%=0 TO 2 STEP 2
   40 P%=c%
   50 [opt p%
   60 .start
   70 SWI "OS_EnterOS"
   80 ; in SVC mode now, should be able to access SuperIO
   90 .probe
  100 ldr   r10,superiobase
  110 add   r1,r10,#&3f0<<2
  120 mov   r0,#&55
  130 strb  r0,[r1]
  140 strb  r0,[r1]
  150 mov   r0,#&d
  160 strb  r0,[r1]
  170 ldrb  r0,[r1,#4]
  180 cmp   r0,#3
  190 beq   smsc_config
  200 ;else try 370
  210 add   r1,r10,#&370<<2
  220 mov   r0,#&55
  230 strb  r0,[r1]
  240 strb  r0,[r1]
  250 mov   r0,#&d
  260 strb  r0,[r1]
  270 ldrb  r0,[r1,#4]
  280 cmp   r0,#3
  290 beq   smsc_config
  300 ; else not found =(  return -1
  310 mvn   r0,#0
  320 movs  pc,r14
  330 .smsc_config
  340 ; Chip config is at [r1]
  350 mov   r0,#&28
  360 strb  r0,[r1]
  370 mov   r0,#&3f   ; serial0 out IRQ_C, serial1 shares serial0
  380 strb  r0,[r1,#4]
  390 mov   r0,#&aa
  400 strb  r0,[r1]   ; end config
  410 mov   R1,PC
  420 teqp  R1,#3
  430 mov   R0,R0
  440 mov   r0,#0
  450 mov   pc,r14
  460 .superiobase  EQUD &03010000
  470 ]:NEXT
  480 PRINT "Reprogramming superio...";
  490 A%=USR(start)
  500 PRINT "..done, result = ";A%;"."

-----------------------
(sorry, no binary yet; paste it into BASIC in a task window?)


OK, so having built your MAX232 cable onto the UART0 pins, you can now
do:

*pppconnect devices:serial1 115200 defaultroute

and the box will connect to a unix box that you've done something like
this on:
/usr/sbin/pppd /dev/ttyS1 115200 10.10.10.1:10.10.10.2 noauth nocrtscts

(where 10.10.10.1 is the unix box's IP (or another network) and 10.10.10.2
is the STB)

I put this on my Zip disc, together with the 'SIO' program above:

------8<-------- izipfs:$.Auto ---------

izipfs:$.SIO  
pppconnect devices:serial1 115200 defaultroute   
set inet$resolvers 10.10.10.10    
resolverconfig    

----------------------------------------

(10.10.10.10 is my box running named)

Unfortunately a Zip disc is still needed, but hey.  You can turn it
off when it boots.  The only probs I've found so far is that my
FreeBSD kernel can't cope with >1 ppp interface.

I hope this helps people avoid stringing two modems together with a
PABX or something -- viva digitale all the way!


Cheers,

Matt

ps: now that I actually have a use for the thing... does anyone have a
spare they'd sell me?  Mine's a bit too hacked-about-with to live under
the TV now. :)