From: ian <ian>
Date: Sun, 25 Dec 2005 13:04:49 +0000 (+0000)
Subject: getwritebyte_polarity, etc.
X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ijackson/git?a=commitdiff_plain;h=0726c5fcb7d3184e4ababa78dd2367f00eed794c;p=trains.git

getwritebyte_polarity, etc.
---

diff --git a/detpic/reverse.asm b/detpic/reverse.asm
index abe7eb0..1e57c37 100644
--- a/detpic/reverse.asm
+++ b/detpic/reverse.asm
@@ -173,12 +173,18 @@ board_next_none
 board_next_none_more_message
 	panic	morse_RL
 
+;----------------------------------------------------------------------
+polarity_master_init
+	panic	morse_URM
+	; need to set up polarity_cmds
+
 ;----------------------------------------------------------------------
 needwrite_polarity
-;  <something>_needwrite will see if we need to talk to a slave
+;  needwrite_<something> will see if we need to talk to a slave
 ;    if not it will simply return
 ;    if we _do_, it will store the slave no. in needwrite_slave
-;    and then pop and return
+;     and then pop and return.  In this case getwritebyte_polarity
+;     on this slave must provide a byte next time it is called.
 ;  nb register usage may need to be adjusted for wiring into mascan i2cm_...
 	mov_lfsr polarity_cmds, 0
 polarity_needwrite_loop
@@ -197,10 +203,23 @@ polarity_needwrite_loop
 	pop
 	return
 
+near_getwritebyteyes code
 ;----------------------------------------------------------------------
-polarity_master_init
-	panic	morse_URM
-	; need to set up polarity_cmds
+getwritebyte_polarity
+;  getwritebyte_<something> finds a byte to write to a particular
+;   slave.  If we have something to write, puts the byte in W
+;   and does `goto getwritebyte_yes'.  Otherwise simply returns.
+;
+;		on entry		return, `no'	branch-away, `yes'
+;  cwslave	slave number		preserved	preserved
+;  W		undefined		trashed		byte for slave
+;
+	mov_lfsr polarity_cmds, 0
+	add_wf	FSR0L
+	mov_fw	INDF0
+	bra_n	getwritebyte_yes
+	; no:
+	return
 
 ;======================================================================
  include final.inc