From: ian <ian>
Date: Sun, 25 Dec 2005 13:03:06 +0000 (+0000)
Subject: lasttelldone documented but not implemented
X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ijackson/git?a=commitdiff_plain;h=1f088bee39dac2508c8512b0c651bee0500197ca;p=trains.git

lasttelldone documented but not implemented
---

diff --git a/detpic/nmra-stream.asm b/detpic/nmra-stream.asm
index 213d5ac..9d816cb 100644
--- a/detpic/nmra-stream.asm
+++ b/detpic/nmra-stream.asm
@@ -29,6 +29,7 @@ nextaction	equ	6	; bit 6: change polarity on next interrupt y/n
 fromserial	res	1	; from-serial buffer location (in buffer bank)
 totrack		equ	FSR2L	; to-track buffer location (in buffer bank)
 totrackbit	res	1	; bit location of pointer within byte
+lasttelldone	res	1	; last nmra msg we've told host we've finished
  ;
  ; buffers are each 16 bytes (this is hardwired)
  ; and there are four of them starting at 0x500, 0x510, 0x520, 0x530.
@@ -46,6 +47,20 @@ totrackbit	res	1	; bit location of pointer within byte
  ; being transmitted; if nothing is currently being transmitted
  ; because there is no nmra data at all then totrack points to the
  ; start of the same buffer as fromserial
+ ;
+ ; lasttelldone points to the last buffer whose complete transmission
+ ; we've reported to the host.
+ ;
+ ; We maintain the following properties, notionally:
+ ;
+ ;  lasttelldone <= totrack <= fromserial < lasttelldone
+ ;                           
+ ;              /             \
+ ;             '               `- equal if we have nothing but
+ ;  equal if we have               idle to trasmit
+ ;  told the host about our
+ ;  current buffer state
+ ;
 
 bufferpage	equ	5