Serout code space

[Art]

Hi Guys,
I thought it should be possible to save space if bit banging serial manually.
Maybe just if one speed, or one direction is needed, which is transmit only in this case,
and the byte value is destroyed by the send each time.
That’s what the code is. The delay of course depends on the baud rate you want, and the pic’s clock speed.

Now I’m thinking on the receive side, a fast enough pic should be able to determine the received baud rate
with the very first received byte, by measuring the duration of the start to stop bit,
rather then sending a known byte value and trying to receive at each baud rate until it’s interpreted properly.

‘ PBP software serial out 8N1
delay var word ‘ set baud rate delay
txbyte var byte ‘ byte to send
count var byte ‘ counter

delay = 0’ set serial delay here

main:
txbyte = “H"
GOSUB serialout
txbyte = “E"
GOSUB serialout
txbyte = “L"
GOSUB serialout
txbyte = “L"
GOSUB serialout
txbyte = “O"
GOSUB serialout
txbyte = $20 ‘ space
GOSUB serialout
goto main


serialout:
‘ start bit
PORTB.1 = 0’ tx clear
PAUSEUS delay ‘ start bit delay

‘ send byte
FOR count = 0 TO 7
IF txbyte.bit0 = 1 THEN
PORTB.1 = 1
ELSE
PORTB.1 = 0
ENDIF
txbyte = txbyte >> 1
PAUSEUS delay ‘ data bit delay
NEXT count
PORTB.1 = 1
PAUSEUS delay ‘ stop bit delay
RETURN

[HenrikOlsson]

Hi Art,
Interesting. I suppose you've verified that it actually is "better"? By how much? I think it's not really fair to compare against SEROUT. Instead, you should compare against DEBUG since it, just like your routine, handles the baudrate calculation at compile time - unlike SEROUT/SEROUT2.

Like compare your code with

DEFINE DEBUG_REG PORTB
DEFINE DEBUG_BIT 1
DEFINE DEBUG_BAUD 2400

Main:
DEBUG "Hello", $20
Goto Main

I might be missing something but as far as I can see the problem with doint autobaud detect on an unknown byte is you don't know what the first databit after the startbit actually is so you don't really KNOW if the next edge is the end of the startbit or the end of any arbitrary databit. I believe a common byte is either $55 or $AA because every bit changes.

In any case, please keep posting about your findings!

/Henrik.

[Art]

Haha, you’re right there. I can’t even measure the start bit alone because the next bit could be either value.
I didn’t consider that!

IIRC, 2400 baud timing is 417uS, so you’d maybe subtract a little from that to make up for the instruction time of the serial code itself.
No, it’s not fair to compare with Serout, and Debug didn’t even occur to me.

So long as I could use asm like PBP compiler does in the end, it could be smaller.
When I did decompile PBP in the past, all bytes were sent to functions like this via it’s intermediate system variables,
so that’s an extra copy for nothing:

Your PBP var -> system var -> serial routine

Unless that has been changed in further PBP revisions, it’s still one up
It also occurred to me since last night that serial input code may, or may not be included in a PBP program if only output code is used.

Ps. It probably goes without saying, the main loop in that example was verbose for readability, and should be replaced by reading the data out of an array!

[Art]

and:

IF txbyte.bit0 = 1 THEN
PORTB.1 = 1
ELSE
PORTB.1 = 0
ENDIF

should be replaced with:

PORTB.1 =  txbyte.bit0

While still in BASIC.

[richard]

IT MAY NOT BE WORTH THE EFFORT ,tried this on a 12f683

90 words

#CONFIG
    __config _INTRC_OSC_NOCLKOUT & _WDT_OFF & _MCLRE_ON & _CP_OFF
#ENDCONFIG
DEFINE OSC 8 'LETS PBP KNOW WE WILL BE RUNNING AT 8MHZ

'PIN DEFENITIONS
'
'GP3 
'GP4 USED FOR TRIGGER INPUT
'GP5 USED FOR LED
'SET UP THE  REGISTERS
OSCCON = %01110001  '8MHZ INTERNAL CLOCK USED
CMCON0 = %00000111 'CIN PINS ARE I/O, COUT PIN IS I/O
TRISIO = %00111011 ' GP2  OUTPUT THE REST ARE INPUTS 
ANSEL = 0 'NO ANALOG PORTS - ALL DIGITAL
WPU = %00010000 'GP4 WEAK PULL UP ENABLED.
    
    DEFINE DEBUG_REG GPIO
    DEFINE DEBUG_BIT 2
    DEFINE DEBUG_BAUD 9600
    DEFINE DEBUG_MODE 0
'    LATB.7=1
'PBP software serial out 8N1
delay var word ' set baud rate delay
txbyte var byte ' byte to send
bcount var byte ' counter
serpin var gpio.2
delay = 100 ' set serial delay here   9600
main:
txbyte = "H"
GOSUB serialout
txbyte = "E"
GOSUB serialout
txbyte = "L"
GOSUB serialout
txbyte = "L"
GOSUB serialout
txbyte = "O"
GOSUB serialout
txbyte = $20 ' space
GOSUB serialout
goto main
 
serialout:
Debug  txbyte 
RETURN

98 words for arts version

#CONFIG
    __config _INTRC_OSC_NOCLKOUT & _WDT_OFF & _MCLRE_ON & _CP_OFF
#ENDCONFIG
DEFINE OSC 8 'LETS PBP KNOW WE WILL BE RUNNING AT 8MHZ

'PIN DEFENITIONS
'
'GP3 
'GP4 USED FOR TRIGGER INPUT
'GP5 USED FOR LED
'SET UP THE  REGISTERS
OSCCON = %01110001  '8MHZ INTERNAL CLOCK USED
CMCON0 = %00000111 'CIN PINS ARE I/O, COUT PIN IS I/O
TRISIO = %00111011 ' GP2  OUTPUT THE REST ARE INPUTS 
ANSEL = 0 'NO ANALOG PORTS - ALL DIGITAL
WPU = %00010000 'GP4 WEAK PULL UP ENABLED.
    
'PBP software serial out 8N1
delay var word ' set baud rate delay
txbyte var byte ' byte to send
bcount var byte ' counter
serpin var gpio.2
delay = 100 ' set serial delay here   9600
main:
txbyte = "H"
GOSUB serialout
txbyte = "E"
GOSUB serialout
txbyte = "L"
GOSUB serialout
txbyte = "L"
GOSUB serialout
txbyte = "O"
GOSUB serialout
txbyte = $20 ' space
GOSUB serialout
goto main
 
serialout:

' start bit
serpin = 0  ' tx clear
PAUSEUS delay ' start bit delay
' send byte
FOR bcount = 0 TO 7
serpin=txbyte.0
txbyte = txbyte >> 1
PAUSEUS delay ' data bit delay
 
NEXT  
serpin= 1
PAUSEUS delay ' stop bit delay
RETURN

[Art]

Nice
If it could be matched in space, I’d still prefer to see my own code, just that I’ve never had a reason to do it until now.
It would be less in asm though, and I still think I could top it.

It was worth the effort to do with a dsPic where the pin was not mappable to UART, so incidentally tried with PBP as well.

No BASIC For/Next loop, instead I’d count down to zero.
No shift command, instead an asm rotate to ensure only 1 instruction,
My own delay routine, which is conveniently right before a return, so can be called multiple times.
watchdog timer resets also have to be turned off because PBP won’t put them in it’s own routines, but in YOUR code.

To my disadvantage, there needs to be some value stored in Delay, which would claim some more space.


Something like this (untested).. and I can’t remember if PBP labels need the underscore or not.

count var byte
pdelay var byte

serialout:
@ movlw	,8
@ movwf	_count	,F
@ clrf PORTB	,1
@ call pausedelay
sendbyte:
PORTB.1 = txbyte.bit0
@ rrf txbyte	,F
@ call pausedelay
@ decfsz _count
goto sendbyte
@ bsf PORTB	,1
pausedelay:
@ movlw	,210
@ movwf	_pdelay	,F
zpausedelay:
decfsz _pdelay
@ goto zpausedelay
@ return