; Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
;
; SPDX-License-Identifier: BSD-3-Clause
;

.program iso7816_tx
.side_set 1 opt

; An ISO7816-3 UART transmit program. Adapted from pico-examples/pio/uart_tx/uart_tx.pio
; OUT pin 0 and side-set pin 0 are both mapped to UART TX pin.

; The general idea is 

	pull	   side 1 [4]	; Assert stop bit, or stall with line in idle state
	set x, 8   side 0 [4]	; Preload bit counter, assert start bit for 5 clocks
bitloop:			; This loop will run 8 times (8n1 UART)
	out pins, 1		; Shift 1 bit from OSR to the first OUT pin
	jmp x-- bitloop   [3]	; Each loop iteration is 5 cycles.

	set x, 8   side 1 [4]	; one additional stop bit so we get to GT=12etu


% c-sdk {
#include "hardware/clocks.h"

static inline void iso7816_tx_program_init(PIO pio, uint sm, uint offset, uint pin_tx, uint baud)
{
	// Tell PIO to initially drive output-high on the selected pin, then map PIO
	// onto that pin with the IO muxes.
	pio_sm_set_pins_with_mask(pio, sm, 1u << pin_tx, 1u << pin_tx);
	pio_sm_set_pindirs_with_mask(pio, sm, 1u << pin_tx, 1u << pin_tx);
	pio_gpio_init(pio, pin_tx);

	pio_sm_config c = iso7816_tx_program_get_default_config(offset);

	// OUT shifts to right, no autopull
	sm_config_set_out_shift(&c, true, false, 32);

	// We are mapping both OUT and side-set to the same pin, because sometimes
	// we need to assert user data onto the pin (with OUT) and sometimes
	// assert constant values (start/stop bit)
	sm_config_set_out_pins(&c, pin_tx, 1);
	sm_config_set_sideset_pins(&c, pin_tx);

	// SM transmits 1 bit per 5 execution cycles.
	float div = (float)clock_get_hz(clk_sys) / (5 * baud);
	printf("baud=%u, div=%f\n", baud, div);
	sm_config_set_clkdiv(&c, div);

	pio_sm_init(pio, sm, offset, &c);
	pio_sm_set_enabled(pio, sm, true);
}

static inline bool compute_even_parity_bit(uint8_t x)
{
        x ^= x >> 4;
        x ^= x >> 2;
        x ^= x >> 1;
        return (x) & 1;
}

static inline void iso7816_tx_program_putc(PIO pio, uint sm, uint8_t c)
{
	uint32_t c_with_parity = c;

	if (compute_even_parity_bit(c))
		c_with_parity |= 0x100;

	pio_sm_put_blocking(pio, sm, c_with_parity);
}

static inline void iso7816_tx_program_puts(PIO pio, uint sm, const uint8_t *s, size_t s_len)
{
	while (s_len--)
		iso7816_tx_program_putc(pio, sm, *s++);
}

%}