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Forum Index : Microcontroller and PC projects : Pico PIO Development
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| Author | Message | ||||
led-bloon Senior Member  Joined: 21/12/2014 Location: AustraliaPosts: 202 |
I stand corrected led Miss you George |
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| utop25 Newbie  Joined: 24/05/2022 Location: AustraliaPosts: 5 |
Thanks to all for your help. I now have a squarewave on GP02. |
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phil99 Guru  Joined: 11/02/2018 Location: AustraliaPosts: 1781 |
For the manual it may be more instructive using a pin other than the default as in Peter's example. eg. '1kHz square wave output on pin4 (GP2) Dim a%(7)=(&H0001E000E101E081,0,0,0,0,0,0,0) SetPin GP2,Pio1 PIO program 1,a%() PIO init machine 1,0,4000, Pio(pinctrl 0,1,,,,GP2) PIO start 1,0 Have tested it up to 20MHz (the limit of my multimeter). Could be useful. Minimum frequency is 961.25 Hz as "Clock must be in range 3845 to 252000000" so max. should be 63 MHz. Using a lower CPU speed lowers these limits in proportion. . Edited 2022-05-29 18:23 by phil99 |
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| Volhout Guru Joined: 05/03/2018 Location: NetherlandsPosts: 3516 |
There is no specific thread for pico PIO development except this one. So I post this here. In my research for the programming challenge for 2022, I developed a SSTV program that makes use of the PIO sequencer (in the VGA picomite). This PIO program measures the frequency of the signal at pico pin GP0 and turns it into a number. Prior to this however I did some experiments with the PIO sequencer to achieve the same in a different manner. This experiment measures the input frequency at pin GP0, and displays the result on LED's at GP1....GP5. It discriminates between the SSTV specific frequencies 1900Hz (at GP1) for VIS leader signa 1500Hz (at GP2) for video black level 1300Hz (at GP3) for VIS logic "0" 1200Hz (at GP4) for SYNC signal 1100Hz (at GP5) for VIS logic "1" Since this program uses PIO to SET pins, to MOV values from X register to GPIO pins, and uses the PIO instruction (post) DELAY to achieve timing this may be instructive to others who want to play with PIO. 'use PIO discriminator frequency on pin GP0 - works with PWM in 'to be used for SSTV reception 'since pixel clock in sstv is 0.572ms and lowest freq is 1500Hz (0.666ms) 'we measure half of input cycle (low half) at max 0.333ms 'shortest time is 1900Hz (white video) 'since we process only 1 bit, threshold is set to 1700Hz (0.294ms) '1900Hz...1700Hz = white (GP1) 'threshold = 294us '1700Hz...1500Hz = black (GP2) 'threshold = 333us (delta = 333-294 = 39) '1500Hz...1250Hz = space = logic 0 (GP3) 'threshold = 400us (delta = 400 - 333 = 67) '1250Hz...1150Hz = sync (GP4) 'threshold = 434us (delta = 434 -499 = 34) '1150Hz...0 = mark = logic 1 (GP5) SetPin gp1,pio1 SetPin gp2,pio1 SetPin gp3,pio1 SetPin gp4,pio1 SetPin gp5,pio1 'PIO 1 sequncer 0 is the frequency discriminator 'clock is set to 100kHz (10us) 'delay in the instructions is tuned to achieve correct timing 'generate test signal on GP0 SetPin gp0,pwm0a PWM 0,1900,50 CLS 'pio program '0 00C0 'wait for gp0 to become low (gp0 is not in GPIO map) '1 E09F 'set pindirs gp1..gp5 out '2 FA21 'set X=1 delay 26 ticks (260us) '3 00CB 'jmp (gp0=1) to setpins '4 E422 'set X=2 delay 4 ticks (40us) '5 00CB 'jmp (gp0=1) to setpins '6 E324 'set X=4 delay 3 ticks (30us) '7 00CB 'jmp (gp0=1) to setpins '8 E228 'set X=8 delay 2 ticks (20us) '9 00CB 'jmp (gp0=1) to setpins 'A E030 'set X=16 delay 0 'B A001 'mov X to pins 'if use fifo 'C A0C1 'mov X to ISR 'D 8000 'push noblock 'z%=&hA0C18000 'use fifo 'C 0000 'jmp 0 z%=0 'not use fifo Dim a%(7)=(&h00CBFA21E09F00C0,&h00CBE32400CBE422,&hA001E03000CBE228,z%,0,0,0,0) 'configure pio1 e=Pio(execctrl 0,0,&h1f) 'use gp0 for PIN s=Peek(word &h503000d0) 'no change from default p=Pio(pinctrl 0,5,5,,,GP1,GP1) 'p=&h14500021 gp1...gp5 for out/mov 'program pio1 and start PIO program 1,a%() PIO init machine 1,0,100000,p,e,s PIO start 1,0 Print "running, input at gp0, status at gp1...gp5" Dim zz%(3) Do Input "typ frequentie :";fr PWM 0,fr,50 Pause 100 'For i=1 To 5 ' Print (Peek(word(&h40014000+i*8)) And 2^17)/2^17, 'Next i 'display FIFI status 'Print "FIFO: ";Hex$(Peek(word &h50300020)) 'display IO pin status (you can also solder LED's to the GP1-GP5 pins) Print Pin(gp1),Pin(gp2),Pin(gp3),Pin(gp4),Pin(gp5) 'read FIFO 'PIO read 1,0,4,zz%() 'actual data 'For i=0 To 3 ' Print "&h";Hex$(zz%(i)), 'Next i Loop Until fr=0 PIO stop 1,0 End For the understanding: the PIO runs at 100kHz. The program starts at address 0 and loops back to it every new cycle. The first instruction in the program is an endless loop until the GP0 pin becomes low. There are 3 instructions (30us) and the 3'rd instruction has a instruction delay added (this is coded inside the instruction) of 26 cycles. This totals for 290us. Then GP0 pin is tested. When the pins is high, the frequency was higher than 1700Hz (threshold 294us), and the value in X is send to the GP1...5. If not, another delay is added, another test is done, and anothervalue written to the GP1...5 pins. This goes on until the lowest frequency (longest period) is tested. To test the system, PWM0A (pin GP0) is supplied with a frequency from PWM0 (50% dutycycle). This is just to verify it works without a external generator. The picomite MMBasic (5.07.05 beta and newer) has a feature that can read the GPIO pins even when they are attached to the PIO. So if you do not plan to solder LED's to the GP1..GP5 pins the program reads the status of the pins and shows them onscreen. When using an older version, you need to PEEK the GPIO input register (the code is in the program, but commented out). If you wonder why there is a double asignment for IO pins in the PIO PINCTRL register, this is becuase the pin direction (pindirs) is done using the SET instruction. Where as sending data to the pins uses the MOV instruction. And these can be assigned to different ranges. In this cas the ranges overlap. I hope some of you will study this and become a little more knowledged how the PICO PIO works. It is a great instrument with many options. Edited 2022-06-06 06:35 by Volhout PicomiteVGA PETSCII ROBOTS |
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