micropython · NitiKaur · Jul 6, 2021 · Jul 13, 2021 · Jul 13, 2021 · Jul 13, 2021
diff --git a/docs/rp2/pio.rst b/docs/rp2/pio.rst
@@ -0,0 +1,79 @@
+.. _rp2_pio:
+
+RP2040 has standard hardware support like I2C, SPI and UART for communication
+protocols with standard devices. For devices where we do not have hardware
+support for such protocols or where there is a requirement of more I/O
+channels, PIO(Programmable Input Ouput) comes intp play. Also, typical
+micropython devices make use of a technique called bit banging which is pins
+are rapidly turned on and off to transmit data. This makes the entire process
+very slow as the processor concentrates on bit banging rather than exceuting
+any other process. However, PIO sllows it to carry on with the bit banging
+process while the processor resources are used for executing some other work. 
+
+Along with the two main cotex - MO+ processing cores, RP2040 has two PIO
+blocks each of which has four state machines. These state machines take
+process data in FIFO (FIrst-In-First-Out) format. When these state machines
+are free, they will put in data from the queue and execute the instruction.
+This way, the PIO state machines and the main process works simultaneously
+without being much dependant on the other. 
+
+Eaxh FIFO has four words (each of 32 bits) which can be linked to the DMA toin assemby
+transmit larger amounts of data to the PIO state machine and allows it to
+carry on execution without the main program keeping a track of it at each
+instant of time.
+
+Each state machine has a set of instructions- which allow for a wide range of
+behaviourial or location changes to the data. They are written in assembly
+language which is later used in a MicroPython program to perform specific
+tasks. These instructions are -
+
+jmp(cond, lebel=None)
+	condition : 0-7
+	<delay_value> : 0-31
+	target : instruction offset of label within the program
+    see sec 3.4.2 of RPi docs for details
+
+wait(polarity, src, index)
+     polarity: 0-1
+     src: gpio, pin, irq
+     index: 0-31
+     wait for high/low on pin 0-31 or irq 0-31
+     see sec 3.4.3 of RPi docs for details
+
+in(src, data)
+	src : pin, X, Y, ISR, OSR(all 0-31)
+	data : bit count(0-31)
+    see sec 3.4.4 of RPi docs for details
+
+out(dist,data)
+	dist : pin, X, Y, PINDIRS, AC, ISR, OSR(all 0-31)
+	data : bit count(0-31)
+    see sec 3.4.5 of RPi docs for details
+
+push(value = 0, value = 2)
+    	block = 0 : no block
+    block = 1 : block
+    see sec 3.4.6 of RPi docs for details
+
+pull(value = 0, value = 2)
+	pull(if empty) : 1 (default = 0)
+	block : 1 (default = 1)  
+	no-block = 0
+    see sec 3.4.7 of RPi docs for details
+
+mov(dist, src)
+	dist : pin, X, Y, ISR, OSR, PC (all 0-31)
+	src : pin, X, Y, ISR, OSR (all 0-31)
+    see sec 3.4.8 of RPi docs for details
+
+irq(mod, index = None)
+	index : IRQ (0-7)
+    see sec 3.4.9 of RPi docs for details
+
+self(dest, data)
+	dest : X, Y, PINS, PINDIRS
+	data : value (0-31)
+    see sec 3.4.10 of RPi docs for details
+
+
+