trs80: implement a standalone RS-232 driver

No more relying on the TRS-DOS driver!

arch/z80/trs80/blk.fs

@@ -100,9 +100,10 @@ EXX, ( unprotect BC ) ;CODE
 : FD! ['] @WRSEC SWAP FD@! ;
 : FD$ ['] FD@ BLK@* ! ['] FD! BLK!* ! ;
 
-: _err LIT" *CLerr" ERR ;
-: *CL< 0 BEGIN DROP 0x0238 @GET UNTIL ;
-: *CL> 0x0238 @PUT NOT IF _err THEN ;
+: CL$ 0x02 0xe8 PC! ( UART RST ) 0xee 0xe9 PC! ( 9600 bauds )
+    0b01101100 0xea PC! ( word8 no parity RTS ) ;
+: CL> BEGIN 0xea PC@ 0x40 AND UNTIL 0xeb PC! ;
+: CL< BEGIN 0xea PC@ 0x80 AND UNTIL 0xeb PC@ ;
 ( ----- 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/z80/trs80.txt

@@ -257,8 +257,8 @@ And there we go! A Collapse OS launchable from floppy!
 # Sending blkfs to floppy
 
 As it is, your system fully supports reading and writing to
-floppy drive 1. It also had *CL< to read a char from *cl and
-*CL> to emit a char to *cl.
+floppy drive 1. It also had CL< to read a char from its RS-232
+port and CL> to emit to it.
 
 That's all you need to have a full Collapse OS with access to
 disk blocks.
@@ -267,16 +267,19 @@ First, make sure your floppies are formatted. Collapse OS is
 currently hardcoded to single side and single density, which
 means there's a limit of 100 blocks per disk.
 
-You'll need to send those blocks through RS-232. Begin by taking
-over the prompt:
+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:
 
-    ' *CL> ' EMIT **!
-    ' *CL< ' KEY **!
+    ' CL> ' EMIT **!
+    ' CL< ' KEY **!
 
-See B80 for details about those RAM offsets. Your serial link
-now has the prompt. You will also have to make your newlines
-CRLF. The TRS-80 wants CR only, but serial communications (and
-blkup) expect CRLF:
+See "Aliases" in usage.txt for details. Your serial link now has
+the prompt. You will also have to make your newlines CRLF. The
+TRS-80 wants CR only, but serial communications (and blkup)
+expect CRLF:
 
     ' CRLF ' NL **!