SWD PIO experiments (never tested)

gistfile1.txt

// packet request 1: parity with counter and intermediate reg
// 20 instructions, max swd freq clk/4

.side_set 1

    set pins, 1 side 0 // start
    set x, 3 side 0

reload_even:
    out y, 1 side 1
    jmp !y, even side 1

odd:
    mov pins, y side 0
    jmp x--, reload_odd side 0
    jmp parity side 1 [1] // x == 0, inverse of parity bit

reload_odd:
    out y, 1 side 1
    jmp !y, odd side 1 

even:
    mov pins, y side 0
    jmp x--, reload_even side 0
    set x, 1 side 1 [1] // x is the inverse parity bit, set it to output 0

parity:
    mov pins, !x side 0 [1]
    nop side 1 [1]

    set pins, 0 side 0 [1] // stop
    nop side 1 [1]
    set pindirs, 0 side 0 [1] // park not driven
    nop side 1 [1]
    nop side 0 [1] // turnover
    nop side 1 [1]

// packet request 2: parity with jumps
// 26 instructions, max swd freq clk/2

.side_set 1

    set pins, 1 side 0 // start
    nop side 1

    out pins, 1 side 0
    jmp pin, odd1 side 1
even1:
    out pins, 1 side 0
    jmp pin, odd2 side 1
even2:
    out pins, 1 side 0
    jmp pin, odd3 side 1
even3:
    out pins, 1 side 0
    jmp pin, parity1 side 1
parity0:
    set pins, 0 side 0
    jmp stop side 1

odd1:
    out pins, 1 side 0
    jmp pin, even2 side 1
odd2:
    out pins, 1 side 0
    jmp pin, even3 side 1
odd3:
    out pins, 1 side 0
    jmp pin, parity0 side 1
parity1:
    set pins, 1 side 0
    nop side 1

stop:
    set pins, 0 side 0 // stop
    nop side 1
    set pindirs, 0 side 0 // park not driven
    nop side 1
    nop side 0 // turnover
    nop side 1

// packet request 3: parity from fifo
// 14 instructions, max swd freq clk/2

pub fn calc_parity(inp: u8) -> u8 {
    let masked = inp & 0b1111;
    (masked.count_ones() % 2) as u8
}

.side_set 1 opt

.wrap_target
start:
    pull
    set pins, 1       side 0 // Start
    set x, 2          side 1
next_bit:
    out pins, 1       side 0 // APnDP, RnW, A2
    jmp x--, next_bit side 1
    out pins, 1       side 0 // A3
    pull              side 1 // Get the parity bit, which was computed on the CPU in meantime
    out pins, 1       side 0 // Parity
    nop               side 1
    set pins, 0       side 0 // Stop
    nop               side 1
    set pins, 1       side 0 // Park
    nop               side 1
    set pindirs, 0    side 0 // Turnaround
    set x, 1          side 1
ack_bit:
    in pins, 1        side 0 // ACK0, ACK1
    jmp x--, ack_bit  side 1
    in pins, 1        side 0 // ACK2
    irq ?             side 1

    // read_write sm controls clocking
    mov x, isr
    push
    jmp x!=y, nack
    jmp start
nack:
    set pindirs, 1
.wrap

//////////////////////

.program read

.side_set 1

// autopull 8bit

    mov x, osr
    wait ?
read_bit:
    in pins, 1         side 0
    jmp x--, read_bit  side 1
parity:
    in pins, 1         side 0 // parity
    push               side 1
    set pindirs, 1     side 1

//////////////////////////


.program write

.side_set 1

// autopull

write_bit:
    out pins, 1        side 0
    jmp x--, write_bit side 1
    out pins, 1        side 0 // parity
    nop                side 1

/// LOW SPEED
/////////////

.program swd_packet_request
.sideset 1

.wrap_target
    pull
    set pins, 1       side 0 [1] // Start
    set x, 3          side 1
next_bit:
    nop               side 1
    out pins, 1       side 0 [1] // APnDP, RnW, A2, A3
    jmp x--, next_bit side 1
    pull              side 1 // Get the parity bit, which was computed on the CPU in meantime
    out pins, 1       side 0 // Parity
    set x, 1          side 0
    out pins, 1
    nop               side 1
    set pins, 0       side 0 // Stop
    nop               side 1
    set pins, 1       side 0 // Park
    nop               side 1
    set pindirs, 0    side 0 // Turnaround
    set x, 1          side 1
ack_bit:
    in pins, 1        side 0 // ACK0, ACK1
    jmp x--, ack_bit  side 1
    in pins, 1        side 0 // ACK3
    irq 4             side 1

// write, autopull8

.program swd_read_bits
.sideset 1 opt
.wrap_target
    pull                        ; number of bits - 1
    mov x, osr
    pull                        ; first byte needs a manual pull, next bytes are autopulled
    wait irq, 1
next_bit:
    out pins, 1         side 0  ; clock data out on falling edge
    jmp x--, next_bit   side 1  ; data is present for posedge
    irq 2               side 0
.wrap

// read, autopush8
.program swd_write_bits
.sideset 1 opt
.wrap_target
    pull                        ; number of bits - 1
    mov x, osr
    wait irq, 2
    set pindirs, 0      side 1  ; turnaround
next_bit:
    in pins, 1          side 0
    jmp x--, next_bit   side 1
    push                side 0  ; last bytes needs a manual push
    set pindirs, 1      side 1  ; turnaround