From: ian <ian>
Date: Tue, 22 Nov 2005 22:57:28 +0000 (+0000)
Subject: change timings to 18wpm morse; clever "waiting2 bsr waiting // waiting ..." trick... 
X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ijackson/git?a=commitdiff_plain;h=f23f5a5ac94e609a59869ab9b44da9c4d3721051;p=trains.git

change timings to 18wpm morse; clever "waiting2 bsr waiting // waiting ..." trick (and must therefore reset stack pointer)
---

diff --git a/detpic/panic.asm b/detpic/panic.asm
index 7e724fb..3678ac1 100644
--- a/detpic/panic.asm
+++ b/detpic/panic.asm
@@ -42,15 +42,14 @@ panic_routine
 ;  panicing which would be bad because we might forget to panic).
 
         mov_wf   panic_address
-
+	clr_f	 STKPTR		; avoids stack overruns
 
 ; re-initialise timer0 config
-        bc_f     T0CON,6       ; p107 Timer0 -> 16bit mode
-        bc_f     T0CON,5       ; timer0 use internal clock
-        bc_f     T0CON,3       ; use prescaler
-        bc_f     T0CON,2       ; }
-        bs_f     T0CON,1       ; } prescale value 1:8 (13ms x 8)
-        bc_f     T0CON,0       ; }
+	mov_lw	(1<<TMR0ON) | 011b ; Enable, 16-bit, timer, prescaler 1:16
+	mov_wf	T0CON	; => PSout is 312.5kHz or 3.2us per period  (DS p108)
+ ; We want to wait 66ms (morse at 18wpm according to the PARIS standard
+ ; is a unit time of 66ms), or 20,833 PSout cycles:
+waiting_t0cycles equ 20833 ; see by `waiting', below
 
 ; get # bytes of morse msg, # registers in panic readout, message start addr.
 ; back from condensed message start addr. stored in panic_address
@@ -78,22 +77,14 @@ panic_loop
 	swap_f	panic_regs	; panic_regs now contains # registers to read
 
 	call	led_black
-	call	waiting
-	call	waiting
-	call	waiting
-	call	waiting
-	call	waiting
-	call	waiting
-	call	waiting
-	call	waiting
+	call	waiting16
 	call	morsemsg	; transmit morse in red
 	call	led_black
-	call	waiting
-	call	waiting
-	call	waiting
-	call	waiting
+	call	waiting8
+	call	waiting4
 	call	registermsg	; transmit contents of registers in 
 				; red(=low) and blue(=high)
+	call	waiting16
         goto    panic_loop
 
 ;****************************************************************************
@@ -184,8 +175,7 @@ register_loop
 
 	inc_f		register_counter	;increment loop counter
 
-	call		waiting
-	call		waiting
+	call		waiting8
 	goto		register_loop
 
 ;--------------------------
@@ -217,7 +207,7 @@ register_readout_loop
         cmp_fw_ifne	bit_counter	; if loop counter !=4 (nybble length), 
 					; skip insertion of extra black space
 	goto		not_nybble_boundary
-	call		waiting
+	call		waiting4
 
 not_nybble_boundary
         rl_f	   	flash_pattern           ; top bit goes into N flag, 
@@ -243,13 +233,20 @@ register_readout_endif_led
 ; GENERAL SUBROUTINES
 
 ;----------------------------------------
+waiting16	rcall	waiting8
+waiting8	rcall	waiting4
+waiting4	rcall	waiting2
+waiting2	rcall	waiting
 waiting
 ; waits for a fixed interval, depending on the configuration of TMR0
 
         bc_f   	INTCON,2      	; clear timer0 interrupt bit (p109)
-        clr_f  	TMR0H         	; p107 set high byte of timer0 to 0 (buffered,
+; Interrupt happens on overflow.  So start at 65535-waiting_t0cycles:
+	mov_lw	(65535-waiting_t0cycles) / 256
+	mov_wf	TMR0H		; p107 set high byte of timer0 (buffered,
                                 ; only actually set when write to tmr0l occurs)
-        clr_f  	TMR0L         	; set timer0 low byte - timer now set to 0000h
+	mov_lw	(65535-waiting_t0cycles) & 0xff
+        mov_wf 	TMR0L         	; set timer0 low byte - timer now set
 waiting_loop
         bt_f_if0 INTCON,TMR0IF    	
         bra     waiting_loop	; wait for timer0 interrupt