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

diff --git a/detpic/nmra-stream.asm b/detpic/nmra-stream.asm
index 7d010362cbddb60fb45a2f82019bfb63b9fc6573..f88fbf4f2738308648f761bf3eddfa6919acf832 100644 (file)
--- 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
 
 ;****************************************************************************