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Forum Index : Microcontroller and PC projects : revisit picomite PIO - measure period
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| Volhout Guru  Joined: 05/03/2018 Location: NetherlandsPosts: 3496 |
In the early days of picomite development, I played with the PIO inside the picomite. After some initial investigations, I dropped the topic, in favour of other picomite functions. Now, after a year, I wanted to pick it up again, and found my knowledge was very rusty. I did not even know how to assemble (compile) the code, tried using PASM12a (Mixtel90). After a lot of "aha"'s I finally have something working, and I wanted to share it with you. Maybe it may serve others to shorten their introduction to PIO. This program uses the PIO to measure period (1/frequency) of an incoming signal. To achieve this it uses the "JMP PIN" PIO instruction. You can assign any of the 32 GPIO pins to this instruction. The PIN does not have to be in the SET PIN map, it is completely independent of the PINCTRL settings. It can also be a pin the is connected to an internal PWM (as shown in the example). To test the measurement function, the PIO is measuring the frequency of GP0 that is driven from a PWM running at 1kHz. The register adresses used (&h503000xx) refer to PIO 1. Similar use &h502000xx when using PIO 0). I hope this is of some benefit to others. 'PIO measure period - this works !!! 'The program uses a PMW output to generate a test frequency, just to test the function 'the PIO (PIO1 sequencer 0 in this example) measures the period (1/frequency) of the incomming signal at GPx 'the signal must be logic level. For this example the sequencer runs at 1MHz, gives a 500kHz (2us) resolution 'of the measured clock. 'generate 1khz test tone on GP0 SetPin gp0,pwm0a PWM 0,1000,50 ' PIO1 program, measure period on GPx (depends on PIN setting EXECCTRL register) ' the period is 2*TC*(count+3), where TC= PIO clock frequency ' '0 set x 0 E020 clear X '1 mov x -x A029 change X to -1 (ffffffff) '2 jmp pin 4 00C4 when pin=1 goto count loop 2 '3 jmp x-- 2 0042 count loop 1 (while PIN=low) '4 jmp x-- 5 0045 count loop 2 (while PIN=high) '5 jmp pin 4 00C4 '6 mov -x isr A0C9 finished counting, move X to shift register '7 push noblock 8000 and push shif register to FIFO '8 jmp always 0 0000 in future may be replaced by .wrap ' Dim a%(7)=(&h004200c4a029E020,&h8000a0c900c40045,0,0,0,0,0,0) SetPin gp1,pio1 'not sure if this is needed 'configure the PIO sequencer clock and pin registers e=Pio(execctrl 0,0,&h1f) 'use pin gp0 (no external wire, snoop pin GP0) 'e=Pio(execctrl 1,0,&h1f) 'use pin gp1 (external wire to GP0) s=Peek(word &h503000d0) 'just to get default value reprogrammed p=0 'no IO pins used except PIN in JMP (not part of this register) 'program the above program in the PIO and setup the machine, and start it. PIO program 1,a%() PIO init machine 1,0,1000000,p,e,s PIO start 1,0 'wait a moment for data to get collected Pause 100 'read the top of the PIO FIFO one word at at time. Since you start measuring at a 'random moment, the first reading can be wrong (incomplete cycle). Do count = Peek(word &h50300020) 'reads the fifo register period = 2 * (count + 3) print "the period measured is ";period;" us" Pause 100 Loop While Inkey$="" PIO stop 1,0 End PicomiteVGA PETSCII ROBOTS |
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Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 5705 |
Lovely to see a real-life application for the PIO. :) I know VGA uses it, but that's getting complicated. lol Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| matherp Guru Joined: 11/12/2012 Location: United KingdomPosts: 8567 |
Did PIO READ not work? I note you are peeking the register. |
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| Tinine Guru Joined: 30/03/2016 Location: United KingdomPosts: 1646 |
Couldn't agree more  Some serious HP here that I also would like to tap. Craig |
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| Volhout Guru Joined: 05/03/2018 Location: NetherlandsPosts: 3496 |
@Peter No, not really. So I used the peek method. Dim h%(3) PIO read 1,0,4,h%() Print h%(1) gives error [42] PIO read 1,0,4,h%() Error : Invalid syntax PicomiteVGA PETSCII ROBOTS |
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