trs80: Improve RS-232 driver

I could drive my RC2014 from my TRS-80 4P (using the Remote Shell
coming in the next commit)! A challenge I faced was that the RC2014
spits characters too fast and the CTS line of its ACIA modules
(both the 6850 and SIO/2 ones) are hard-wired to ground, making
flow control difficult. I solved this, for now, by lowering comm
speed.

This driver improvement makes CL<? faster and makes baud rate
configurable in CL$.

arch/z80/trs80/blk.fs

@@ -9,7 +9,7 @@ Load with "602 LOAD".
 
 There is also the RECV program at B612.
 ( ----- 602 )
-1 8 LOADR+
+1 9 LOADR+
 ( ----- 603 )
 CODE (key?) ( -- c? f )
     A 0x08 LDri, ( @KBD )
@@ -100,10 +100,19 @@ EXX, ( unprotect BC ) ;CODE
 : FD! ['] @WRSEC SWAP FD@! ;
 : FD$ ['] FD@ ['] BLK@* **! ['] FD! ['] BLK!* **! ;
 
-: CL$ 0x02 0xe8 PC! ( UART RST ) 0xee 0xe9 PC! ( 9600 bauds )
-    0b01101100 0xea PC! ( word8 no parity RTS ) ;
+( ----- 611 )
+: CL$ ( baudcode -- )
+0x02 0xe8 PC! ( UART RST ) DUP 4 LSHIFT OR 0xe9 PC! ( bauds )
+    0b01101101 0xea PC! ( word8 no parity no-RTS ) ;
 : CL> BEGIN 0xea PC@ 0x40 AND UNTIL 0xeb PC! ;
-: CL< BEGIN 0xea PC@ 0x80 AND UNTIL 0xeb PC@ ;
+CODE _
+    0xea INAi, 0x80 ANDi, IFZ, PUSH0, ELSE,
+    0xeb INAi, PUSHA, PUSH1, THEN,
+;CODE
+: CL<? _ IF 1 EXIT THEN
+    0b01101100 0xea PC! ( RTS )
+    1 TICKS ( 100 us ) _
+    0b01101101 0xea PC! ( no-RTS ) ;
 ( ----- 612 )
 ( We process the 0x20 exception by pre-putting a mask in the
   (HL) we're going to write to. If it wasn't a 0x20, we put a

doc/hw/acia.txt

@@ -28,3 +28,16 @@ can be raised) very much. We have to take extra care, when
 communicating from modern system, not to send too much data too
 fast. But for COS-to-COS communication, this simple system
 works.
+
+# Broken hardware
+
+Some designs are broken with this scheme. For example, the
+RS2014 SIO module hard-wires CTS to GND because the FTDI
+connector doesn't have such a pin (modern computers can always
+handle the load).
+
+In these cases, a solution would be to use Break signals as a
+workaround, but I prefer avoiding complexity for now. So when
+you deal with broken design, you'll have to sidestep it either
+by implementing your own Break handling or by lowering com-
+munication speed.

doc/hw/z80/trs80.txt

@@ -270,8 +270,15 @@ means there's a limit of 100 blocks per disk.
 You'll need to send those blocks through RS-232. First, let's
 initialize the driver with CL$. This driver does not require
 the TRS-DOS driver to be loaded. Also, it is hardcoded to
-"no parity, 8 bit words, 9600 bauds". Now, let's have the CL
-take over the prompt:
+"no parity, 8 bit words". And takes a "baud code" as an argu-
+ment. It's a 0-15 value with these meanings:
+
+00 50          01 75           02 110          03 134.5 
+04 150         05 300          06 600          07 1200 
+08 1800        09 2000         0a 2400         0b 3800 
+0c 4800        0d 7200         0e 9600         0f 19200
+
+After CL$ is called, let's have the CL take over the prompt:
 
     ' CL> ' EMIT **!
     ' CL< ' KEY **!