maple_out.pio

; maple_out notes:
; - It is up to the system to ensure open line before activating this (no overcurrent protection)
; - Since bytes are shifted out "to the left" in order to shift out the most significant bit of each
;   byte first, the most significant byte comes out first too. This means byte order will need to be
;   swapped before feeding into this.

.program maple_out
.side_set 2 opt

.define public MASK_A 0x1
.define public MASK_B 0x2
.define public MASK_AB 0x3

; must be even - minimum number of ticks per edge
; 3 bits are used for sideset, so 4 is the max here
; The logic in this file is tightly coupled to the value of 4 (do not change)
.define public DOUBLE_PHASE_TICKS 4
.define public SINGLE_PHASE_TICKS (DOUBLE_PHASE_TICKS / 2)

.wrap_target
maple_out_start:

; Stalls until first word; first word is how many bits this will send
; The following must be true about x: (x - 8) % 32 == 0 && x >= 40
out x, 32 side MASK_AB



; send out the start sequence
start_sequence:
; First, set pins as output and with A and B set HIGH
set pindirs MASK_AB side MASK_AB [DOUBLE_PHASE_TICKS - 1]
; Bing A LOW for a cycle then toggle B LOW then HIGH 3 times
set y, 3 side MASK_B [DOUBLE_PHASE_TICKS - 1]
start_b_toggle_loop:
nop side 0 [DOUBLE_PHASE_TICKS - 1]
nop side MASK_B [DOUBLE_PHASE_TICKS - 2]
jmp y-- start_b_toggle_loop
; Bring A back HIGH and decrement x in preparation of the first bit
jmp x--, first_clock_a_data_b side MASK_AB

; Don't want to bring B low unless the first bit is 0, so this is a special check
first_clock_a_data_b:
out y, 1 side MASK_AB
jmp !y, clock_a_data_b_zero side MASK_AB
jmp first_clock_a_data_b_one side MASK_AB



; send out packet data
; x scratch register contains how many bits left to send
; y scratch register contains the current bit
clock_a_data_b:
out y, 1 side MASK_A [SINGLE_PHASE_TICKS - 2]
jmp !y clock_a_data_b_zero
; else: fall through to clock_a_data_b_one

clock_a_data_b_one:
nop side MASK_AB [SINGLE_PHASE_TICKS - 1]
first_clock_a_data_b_one:
jmp x-- clock_b_data_a side MASK_B [SINGLE_PHASE_TICKS - 1]
; jmp end_sequence ; should never reach here anyway (saves an instruction)

clock_a_data_b_zero:
nop side MASK_A [SINGLE_PHASE_TICKS - 1]
jmp x-- clock_b_data_a side 0 [SINGLE_PHASE_TICKS - 1] ; just need to decrement x
; jmp end_sequence ; should never reach here anyway (saves an instruction)

clock_b_data_a:
out y, 1 side MASK_B [SINGLE_PHASE_TICKS - 2]
jmp !y clock_b_data_a_zero
; else: fall through to clock_b_data_a_one

clock_b_data_a_one:
nop side MASK_AB [SINGLE_PHASE_TICKS - 1]
jmp x-- clock_a_data_b side MASK_A [SINGLE_PHASE_TICKS - 1]
jmp end_sequence ; extra tick added here which can't be helped

clock_b_data_a_zero:
nop side MASK_B [SINGLE_PHASE_TICKS - 1]
jmp x-- clock_a_data_b side 0 [SINGLE_PHASE_TICKS - 1]
; Else: fall through to end sequence



; send out the end sequence
end_sequence:
out y, 24 side MASK_A [SINGLE_PHASE_TICKS - 1] ; last word only has crc byte to send; purge last 24 bits
nop side MASK_AB [DOUBLE_PHASE_TICKS - 1]
nop side MASK_A [DOUBLE_PHASE_TICKS - 1]
nop side 0 [DOUBLE_PHASE_TICKS - 1]
nop side MASK_A [DOUBLE_PHASE_TICKS - 1]
nop side 0 [DOUBLE_PHASE_TICKS - 1]

; Wait for IRQ to be handled before continuing
irq wait 0 rel side MASK_A

; Allow the application to transition AB back HIGH when it's ready to "submit" the data.
; See MapleOutStateMachine::stop()

.wrap

% c-sdk {
#include "hardware/gpio.h"
#include "hardware/pio.h"
#include "PioProgram.hpp"

#define MAPLE_OUT_PIO pio0

class MapleOutStateMachine
{
    public:
        inline MapleOutStateMachine(uint sys_freq_khz, uint ns_per_bit, uint pin_a) :
            mProgram(getMapleOutProgram()),
            mPinA(pin_a),
            mPinB(pin_a + 1),
            mMaskAB(3 << pin_a),
            mSmIdx(pio_claim_unused_sm(mProgram.mPio, true))
        {
            // Initialize the two pins as inputs with pullups
            gpio_set_dir_in_masked(mMaskAB);
            gpio_set_pulls(mPinA, true, false);
            gpio_set_pulls(mPinB, true, false);

            pio_sm_config c = maple_out_program_get_default_config(mProgram.mProgramOffset);
            sm_config_set_sideset_pins(&c, mPinA);
            sm_config_set_set_pins(&c, mPinA, 2); // just for set pindirs

            // Shift to left, autopull enabled, 32 bits at a time
            sm_config_set_out_shift(&c, false, true, 32);

            sm_config_set_clkdiv(
                &c, (sys_freq_khz * (ns_per_bit / 3 * 2)) / maple_out_DOUBLE_PHASE_TICKS / 1000000.0);

            // Load our configuration, and jump to the start of the program
            pio_sm_init(mProgram.mPio, mSmIdx, mProgram.mProgramOffset, &c);
        }

        inline void start() const
        {
            // Reset pointers
            pio_sm_clear_fifos(mProgram.mPio, mSmIdx);
            pio_sm_restart(mProgram.mPio, mSmIdx);
            pio_sm_clkdiv_restart(mProgram.mPio, mSmIdx);
            pio_sm_exec(mProgram.mPio, mSmIdx, pio_encode_jmp(mProgram.mProgramOffset));
            // Pin direction starts as input
            pio_sm_set_consecutive_pindirs(mProgram.mPio, mSmIdx, mPinA, 2, false);
            // Set this pin's GPIO function (connect PIO to the pad)
            pio_gpio_init(mProgram.mPio, mPinA);
            pio_gpio_init(mProgram.mPio, mPinB);
            // Set the state machine running
            pio_sm_set_enabled(mProgram.mPio, mSmIdx, true);
        }

        inline void stop() const
        {
            pio_sm_set_enabled(mProgram.mPio, mSmIdx, false);
            // Reset the pins' function to standard I/O, transitioning back HIGH before setting to input
            gpio_set_mask(mMaskAB);
            gpio_set_dir_out_masked(mMaskAB);
            gpio_set_function(mPinB, GPIO_FUNC_SIO);
            gpio_set_function(mPinA, GPIO_FUNC_SIO);
            gpio_set_dir_in_masked(mMaskAB);
        }

    private:
        inline static const PioProgram& getMapleOutProgram()
        {
            static const PioProgram program(MAPLE_OUT_PIO, &maple_out_program);
            return program;
        }

    public:
        const PioProgram& mProgram;
        const uint mPinA;
        const uint mPinB;
        const uint mMaskAB;
        const uint mSmIdx;
};

%}