I have been looking at the stream.py example for streaming G-code to Grbl with a more aggressive strategy in order to prevent planner buffer starvation. The example can be found in this repository at: https://github.com/gnea/grbl/blob/master/doc/script/stream.py. On line 164 it says:
while sum(c_line) >= RX_BUFFER_SIZE-1 | s.inWaiting() :
This is the line I am confused about, and before I explain why I am confused, I'll show a snippet of the code surrounding it to give anyone who is reading this a gernal idea of what this section of code is supposed to do:
Send g-code program via a more agressive streaming protocol that forces characters into
Grbl's serial read buffer to ensure Grbl has immediate access to the next g-code command
rather than wait for the call-response serial protocol to finish. This is done by careful
counting of the number of characters sent by the streamer to Grbl and tracking Grbl's
responses, such that we never overflow Grbl's serial read buffer.
g_count = 0
c_line = []
for line in f:
l_count += 1 # Iterate line counter
l_block = re.sub('\s|(.*?)','',line).upper() # Strip comments/spaces/new line and capitalize
l_block = line.strip()
c_line.append(len(l_block)+1) # Track number of characters in grbl serial read buffer
grbl_out = ''
while sum(c_line) >= RX_BUFFER_SIZE-1 | s.inWaiting() :
out_temp = s.readline().strip() # Wait for grbl response
if out_temp.find('ok') < 0 and out_temp.find('error') < 0 :
print " MSG: \""+out_temp+"\"" # Debug response
else :
if out_temp.find('error') >= 0 : error_count += 1
g_count += 1 # Iterate g-code counter
if verbose: print " REC<"+str(g_count)+": \""+out_temp+"\""
del c_line[0] # Delete the block character count corresponding to the last 'ok'
s.write(l_block + '\n') # Send g-code block to grbl
There are two things with line 164 that I don't get. Firstly, why is "1" subtracted from RX_BUFFER_SIZE? Secondly, what is the purpose of using a bitwise OR operation with RX_BUFFER_SIZE-1 and s.inWaiting()? I am not understanding why I can't just do this instead for line 164:
while sum(c_line) >= RX_BUFFER_SIZE:
To me, this would mean that if Grbl's RX buffer is full, we are not going to send more commands, and instead we are going to read acknowledgements coming from the Grbl controller until it is determined that we can send the next block.
My mind turns to mush when I look at this line of code, so forgive me if I am asking stupid questions.
I have been looking at the stream.py example for streaming G-code to Grbl with a more aggressive strategy in order to prevent planner buffer starvation. The example can be found in this repository at: https://github.com/gnea/grbl/blob/master/doc/script/stream.py. On line 164 it says:
while sum(c_line) >= RX_BUFFER_SIZE-1 | s.inWaiting() :This is the line I am confused about, and before I explain why I am confused, I'll show a snippet of the code surrounding it to give anyone who is reading this a gernal idea of what this section of code is supposed to do:There are two things with line 164 that I don't get. Firstly, why is "1" subtracted from RX_BUFFER_SIZE? Secondly, what is the purpose of using a bitwise OR operation with
RX_BUFFER_SIZE-1ands.inWaiting()? I am not understanding why I can't just do this instead for line 164:while sum(c_line) >= RX_BUFFER_SIZE:To me, this would mean that if Grbl's RX buffer is full, we are not going to send more commands, and instead we are going to read acknowledgements coming from the Grbl controller until it is determined that we can send the next block.My mind turns to mush when I look at this line of code, so forgive me if I am asking stupid questions.