Help a PASM noob...
JeeHell
Posts: 3
Hello everyone,
Here is my first real attempt at PASM. Of course, it did not turn out to be working...
The aim is to listen an RF module which outputs data at 9600 bauds. The protocol is serial, but homemade to filter the RF noise.
The same approach worked in SPIN, but I just needed extra ticks to process the data in a more efficient way between two frames.
The emitter will first emit some random bits to set the gain of the RF receiver so noise is less a problem.
Then it sends three bytes in that order:
- first an header (to confirm this is the data we want to receive)
- the data byte
- and again the same data byte (I'll change that to a proper checksum when I get it working...)
Here is the code:
Somehow, I never get more than one high bit in RxBuf, even though I keep outputing data on the RF, and the scope confirms the data is received...
If you have any inputs, ideas, fixes, you're all very welcome. I won't be offended if you say it's badly coded, it truly is my first PASM code (well the 2nd, the first one being a "flashing LED hello world"...)
Best regards,
Jean Luc
Here is my first real attempt at PASM. Of course, it did not turn out to be working...
The aim is to listen an RF module which outputs data at 9600 bauds. The protocol is serial, but homemade to filter the RF noise.
The same approach worked in SPIN, but I just needed extra ticks to process the data in a more efficient way between two frames.
The emitter will first emit some random bits to set the gain of the RF receiver so noise is less a problem.
Then it sends three bytes in that order:
- first an header (to confirm this is the data we want to receive)
- the data byte
- and again the same data byte (I'll change that to a proper checksum when I get it working...)
Here is the code:
DAT
org 0
entry mov RCVpin,#0 'RCVpin is 0, hardcoded for now
mov dRCVpin,#1 'decode RCVpin to...
shl dRCVpin,RCVpin '...binary format
rdlong x,#0 'get CLKFREQ
mov y,baud 'sets y to divide clockfreq by baud
call #divide 'clockfreq/baud
shl x,#16 'we need to get only x[0..15] for...
shr x,#16 '...the result
mov BitTime,x 'bittime=clokfreq/baud
mov rxbyte,#0 'reset rxbyte
mov halfBitTime,BitTime 'computing...
shr halfBitTime,#1 ' ...halfBitTime
mov rxbuf,#0 wz 'reset rxbuf, and set Z flag to 1 at the same time for the muxnz
muxnz dira,dRCVpin 'we must set only the drcvpin to input=>low
Sync mov rxbuf,#0 'reset rxbuf
:loop waitpeq dRCVpin,dRCVpin 'wait for RCVpin to be High
mov t,cnt 'init time reference
mov x,#0 'waitPEQ pattern all to LOW
waitpeq x,dRCVpin 'wait for RCVpin to be Low
sub t,cnt 't=t-cnt
cmp t,halfBitTime wc 'if t<bittime/2 then it's noise,and C flag is set to 1
if_c jmp #:loop
mov t,cnt
add t,halfBitTime
add t,BitTime
getbyte waitcnt t,BitTime 'wait for middle of bit
shl rxbuf,#1 'shift rxbuf left by one bit
test ina,dRCVpin wz
muxnz rxbuf,#1 'if INA & dRCVpin<>0 we put a 1 in the LSB of rxbuf
mov y,rxbuf
and y,sel_HDR
cmp y,HDR wz 'if byteN°3 is the hdr byte we set Z flag to 1
if_nz jmp #getbyte 'if no HDR byte we jump back to read a new bit from RXpin
mov byt,rxbuf 'put rxbuff in byt
shr byt,#8 'we remove the trailer byte
and byt,#$FF 'and also the header byte, so byt is a potential RxByte
mov y,rxbuf
and y,Trail_byte
cmp y,Trail_byte wz 'if byt equals trail byte, we set Z flag to 1
if_nz jmp #getbyte 'if not, we go grab a new bit
mov rxbyte,byt 'so we got a correct RxByte!
jmp #Sync 'and we're happy to try again!
'divide routine by parallax:
'divide x[31.00] by y[15..0] (y[16] must be 0)
'on exit, quotient is i x[15..0] and remainder is in x[31.16]
divide shl y,#15
mov t,#16
:loop cmpsub x,y wc
rcl x,#1
djnz t,#:loop
divide_ret ret
sel_HDR long %11111111_00000000_00000000
HDR long %01010101_00000000_00000000
Trail_byte long %00000000_00000000_11111111
Data_byte long %00000000_11111111_00000000
baud long 9600
RCVpin long 0
dRCVpin res 1
BitTime res 1
halfBitTime res 1
x res 1
y res 1
rxbyte res 1
byt res 1
rxbuf res 1
t res 1
trail res 1
fit 496
Somehow, I never get more than one high bit in RxBuf, even though I keep outputing data on the RF, and the scope confirms the data is received...
If you have any inputs, ideas, fixes, you're all very welcome. I won't be offended if you say it's badly coded, it truly is my first PASM code (well the 2nd, the first one being a "flashing LED hello world"...)
Best regards,
Jean Luc
Comments
One question regarding the test instruction, why would the order of operands matter in this particular case?
Thanks a lot!