From: ian <ian>
Date: Wed, 21 Dec 2005 12:45:57 +0000 (+0000)
Subject: make fromserial update to go to next buffer interrupt-safe; have only one invocation... 
X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ijackson/git?a=commitdiff_plain;h=654ea9e4508abeb9112c27f4bfd595519382162c;p=trains.git

make fromserial update to go to next buffer interrupt-safe; have only one invocation of intrl_handled_nostack
---

diff --git a/detpic/nmra-stream.asm b/detpic/nmra-stream.asm
index 7d01036..f88fbf4 100644
--- a/detpic/nmra-stream.asm
+++ b/detpic/nmra-stream.asm
@@ -39,7 +39,8 @@ totrackbit	res	1	; bit location of pointer within byte
  ; data provided by the host; this means that (fromserial & 0xf0) is
  ; the first buffer which fails to contain a complete nmra message.
  ; fromserial is updated only by the (low priority) serial receive
- ; interrupt handler.
+ ; interrupt handler.  Furthermore, it always maintains a correct
+ ; and valid value for use by the high-priority nmra readout ISR.
  ;
  ; totrack points to the first remaining full byte, which is currently
  ; being transmitted; if nothing is currently being transmitted
@@ -217,7 +218,7 @@ fixme need to check both interrupt handlers here and look for refies too
 	mov_lw	0x0f
 	and_wfw	fromserial
 	bra_z	receive_message_too_long
-
+serial_receive_done
 	intrl_handled_nostack
 
 receive_message_too_long
@@ -231,32 +232,30 @@ end_message
 ; so what's the first byte then ?
 	mov_lw	0xf0
 	and_wff	FSR0L
-	and_wff	fromserial
-	com_fw	INDF0
+	and_wff	fromserial		; fromserial := 00BB0000
+	com_fw	INDF0			;  where BB is this buffer
 	bra_nz	not_nmra_message
 
 ; so, first byte is FF (since complement of it is zero)
 ; so, move to next buffer
 advance_write_buffer
 
-; clear low 4 bits of fromserial and increment top 4 bits
-; aaaabbbb -> bbbbaaaa -> bbbb(aaaa+1) -> 0000(aaaa+1) -> (aaaa+1)0000
+; increment top 4 bits of fromserial (already cleared low 4 bits)
 	debug 	'5'
-	swap_fa	fromserial    
-	inc_fa	fromserial    
-	mov_lw	0xF
-	and_wffa fromserial    
-	swap_fa	fromserial    
+	mov_fw	fromserial		; W =		00BB0000
+	add_lw	0x10			; W =		0?CC0000
+	bc_w	6			; W =		00CC0000
+	mov_wf	fromserial		;  where BB is this buffer
+					;   and CC is next buffer
+ fixme check for overruns ie if we caught up with totrack
 
-; clear bit 6 (will set back to buffer 0 if has overflowed to 4)
-	debug 	'6'
-	bc_fa	fromserial,6  
-	
-	return
+	bra	serial_receive_done
 
 not_nmra_message
+	; we've already set FSR0 and fromserial to point
+	;  back to beginning of the same buffer
 	call	serialrx_generalmsg
-	intrl_handled_nostack
+	bra	serial_receive_done
 
 ;****************************************************************************