
            ;
; Hunter Adams (vha3@cornell.edu)
; HSync generation for VGA driver


; Program name
.program hsync

; frontporch: 16 clocks (0.64us at 25MHz)
; sync pulse: 96 clocks (3.84us at 25MHz)
; back porch: 48 clocks (1.92us at 25MHz)
; active for: 640 clcks (25.6us at 25MHz)
;
; High for 704 cycles (28.16us at 25MHz)
; Low  for 96  cycles (3.84us at 25MHz)
; Total period of 800 cycles (32us at 25MHz)
;


pull block              ; Pull from FIFO to OSR (only happens once)
.wrap_target            ; Program wraps to here

; ACTIVE + FRONTPORCH
mov x, osr              ; Copy value from OSR to x scratch register
activeporch:
   jmp x-- activeporch  ; Remain high in active mode and front porch

; SYNC PULSE
pulse:
    set pins, 0 [31]    ; Low for hsync pulse (32 cycles)
    set pins, 0 [31]    ; Low for hsync pulse (64 cycles)
    set pins, 0 [31]    ; Low for hsync pulse (96 cycles)

; BACKPORCH
backporch:
    set pins, 1 [31]    ; High for back porch (32 cycles)
    set pins, 1 [12]    ; High for back porch (45 cycles)
    irq 0       [1]     ; Set IRQ to signal end of line (47 cycles)
.wrap




% c-sdk {
static inline void hsync_program_init(PIO pio, uint sm, uint offset, uint pin) {

    // creates state machine configuration object c, sets
    // to default configurations. I believe this function is auto-generated
    // and gets a name of _program_get_default_config
    // Yes, page 40 of SDK guide
    pio_sm_config c = hsync_program_get_default_config(offset);

    // Map the state machine's SET pin group to one pin, namely the `pin`
    // parameter to this function.
    sm_config_set_set_pins(&c, pin, 1);

    // Set clock division (div by 5 for 25 MHz state machine)
    sm_config_set_clkdiv(&c, 5) ;

    // Set this pin's GPIO function (connect PIO to the pad)
    pio_gpio_init(pio, pin);
    // pio_gpio_init(pio, pin+1);
    
    // Set the pin direction to output at the PIO
    pio_sm_set_consecutive_pindirs(pio, sm, pin, 1, true);

    // Load our configuration, and jump to the start of the program
    pio_sm_init(pio, sm, offset, &c);

    // Set the state machine running (commented out so can be synchronized w/ vsync)
    // pio_sm_set_enabled(pio, sm, true);
}
%}