Code speed and execution time

[aajgss]

I am using a For/Next loop to sent the variable out to an I2C DAC. The variable is counting from 1 to 255.

The sawtooth waveform only has a frequency of 1.33 hz indication an execution time for each loop of 3mSec.

I am using a 16F690 PIC running at 8Mhz, PBP and MPLAB IDE V8.63. Does this time to execute one loop sound right?

The other question is the number of lines of code compiled. In the MPASM window it tell me the number of lines assembled is 9082. Again does this sound right?

Thanks
aajgss

[cncmachineguy]

Well that does seem really Slloooooowwwww. but maybe a little more info please. code and configs would go a long way here.

[aajgss]

Bert,
Thanks for the quick reply
OK more info - one other question how do I get my code into the scrolling window?

I have a line in there :- i2cread DPin,CPin,$90,1,[c], if I take it out the code doesnt work.


Code

DEFINE osc 20
DEFINE LOADER_USED 1
INCLUDE "MODEDEFS.BAS"
DEFINE I2C_SLOUT
ANSEL =%00000001 ' Enable ADC channel-AN0
ANSELH =%0000
'ADCON0.7 = 1
SSPCON =%00101011
TRISB.4 =0
TRISB.6 =0
TRISA =%00001111
TRISC =%00000000
CPin VAR PORTB.6
DPin VAR PORTB.4
a var word
c var byte

MAINLOOP
for a = 1 to 255
I2Cwrite DPin,CPin,$90,a
i2cread DPin,CPin,$90,1,[c]
next
goto Mainloop

[dhouston]

Add code tags - select the text and then click on # above the edit window.

DEFINE osc 20
DEFINE LOADER_USED 1
INCLUDE "MODEDEFS.BAS"
DEFINE I2C_SLOUT
ANSEL =%00000001 ' Enable ADC channel-AN0
ANSELH =%0000 
'ADCON0.7 = 1
SSPCON =%00101011
TRISB.4 =0
TRISB.6 =0 
TRISA =%00001111 
TRISC =%00000000 
CPin VAR PORTB.6
DPin VAR PORTB.4
a var word
c var byte
 
MAINLOOP
for a = 1 to 255
I2Cwrite DPin,CPin,$90,a
i2cread DPin,CPin,$90,1,[c]
next
goto Mainloop

[cncmachineguy]

The easy to answer question is to put your code in the cool code box, you have to do this:
[ code ]

put code here

[ / code ]

but with no spaces

Still thinking on the real question

[Amoque]

I am not familiar with I2C, but I do notice that in your initial description you say the crystal is 8M, but in the code it is defined 20M...

The rest I do not know, but some thoughts...

Commenting the 2 I2C lines and recompile would give an indication of how much code is actually there (in I2C part)--and how that interface affects speed. The difference (between with no I2C and with I2C) should match pretty closely with datasheet transaction time for DAC chip?

[tenaja]

Using the software implementations of i2c read/write are DREADFULLY SLOW. Yes, I am not surprised you get such a slow loop.

There are several ways to dramatically speed it up.
1. use the hardware i2c--this will speed it up by about 30-40x at least.
2. put the addressing with STARTs, etc, outside the loop, and just clock the data sequentially. This will get you almost 4x improvement.
3. Use a repeat until or do while instead of a for-loop. The For-loop is a lot slower than the other loops when timing is important...but it won't help nearly as much as 1 or 2.
4. Send 256 bytes instead of 255...that way it can init at 0 and loop until 0 again, and that's often a one-instruction savings, depending on the pic.