142 lines
5.6 KiB
Plaintext
142 lines
5.6 KiB
Plaintext
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; Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
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;
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; SPDX-License-Identifier: BSD-3-Clause
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;
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.program hub75_row
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; side-set pin 0 is LATCH
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; side-set pin 1 is OEn
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; OUT pins are row select A-E
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;
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; Each FIFO record consists of:
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; - 5-bit row select (LSBs)
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; - Pulse width - 1 (27 MSBs)
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;
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; Repeatedly select a row, pulse LATCH, and generate a pulse of a certain
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; width on OEn.
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.side_set 2
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.wrap_target
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out pins, 5 [7] side 0x2 ; Deassert OEn, output row select
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out x, 27 [7] side 0x3 ; Pulse LATCH, get OEn pulse width
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pulse_loop:
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jmp x-- pulse_loop side 0x0 ; Assert OEn for x+1 cycles
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.wrap
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% c-sdk {
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static inline void hub75_row_program_init(PIO pio, uint sm, uint offset, uint row_base_pin, uint n_row_pins, uint latch_base_pin) {
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pio_sm_set_consecutive_pindirs(pio, sm, row_base_pin, n_row_pins, true);
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pio_sm_set_consecutive_pindirs(pio, sm, latch_base_pin, 2, true);
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for (uint i = row_base_pin; i < row_base_pin + n_row_pins; ++i)
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pio_gpio_init(pio, i);
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pio_gpio_init(pio, latch_base_pin);
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pio_gpio_init(pio, latch_base_pin + 1);
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pio_sm_config c = hub75_row_program_get_default_config(offset);
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sm_config_set_out_pins(&c, row_base_pin, n_row_pins);
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sm_config_set_sideset_pins(&c, latch_base_pin);
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sm_config_set_out_shift(&c, true, true, 32);
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pio_sm_init(pio, sm, offset, &c);
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pio_sm_set_enabled(pio, sm, true);
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}
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static inline void hub75_wait_tx_stall(PIO pio, uint sm) {
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uint32_t txstall_mask = 1u << (PIO_FDEBUG_TXSTALL_LSB + sm);
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pio->fdebug = txstall_mask;
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while (!(pio->fdebug & txstall_mask))
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tight_loop_contents();
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}
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%}
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.program hub75_data_rgb888
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.side_set 1
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; Each FIFO record consists of a RGB888 pixel. (This is ok for e.g. an RGB565
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; source which has been gamma-corrected)
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;
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; Even pixels are sent on R0, G0, B0 and odd pixels on R1, G1, B1 (typically
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; these are for different parts of the screen, NOT for adjacent pixels, so the
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; frame buffer must be interleaved before passing to PIO.)
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;
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; Each pass through, we take bit n, n + 8 and n + 16 from each pixel, for n in
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; {0...7}. Therefore the pixels need to be transmitted 8 times (ouch) to build
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; up the full 8 bit value for each channel, and perform bit-planed PWM by
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; varying pulse widths on the other state machine, in ascending powers of 2.
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; This avoids a lot of bit shuffling on the processors, at the cost of DMA
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; bandwidth (which we have loads of).
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; Might want to close your eyes before you read this
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public entry_point:
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.wrap_target
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public shift0: ; R0 G0 B0 (Top half of 64x64 displays)
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pull side 0 ; gets patched to `out null, n` if n nonzero (otherwise the PULL is required for fencing)
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out null, 16 side 0 ; discard _
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in osr, 1 side 0 ; Red0
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out null, 32 side 0 ; discard remaining bits
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public shift1:
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pull side 0 ; gets patched to out null, n if n is nonzero (otherwise PULL required)
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in osr, 1 side 0 ; Green0
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out null, 16 side 0 ; << next uint16
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in osr, 1 side 0 ; Blue0
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out null, 32 side 0 ; discard remaining bits
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public shift2:
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pull side 0 ; gets patched to out null, n if n is nonzero (otherwise PULL required)
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out null, 16 side 0 ; discard _
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in osr, 1 side 0 ; Red1
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out null, 32 side 0 ; discard remaining bits
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public shift3: ; R1 G1 B1 (Bottom half of 64x64 displays)
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pull side 0 ; gets patched to out null, n if n is nonzero (otherwise PULL required)
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in osr, 1 side 0 ; Green0, CLK rising edge
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out null, 16 side 0 ; << next uint16
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in osr, 1 side 0 ; Blue0
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out null, 32 side 0 ; discard remaining bits
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in null, 26 side 0 ; Note we are just doing this little manoeuvre here to get GPIOs in the order
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mov pins, ::isr [7] side 1 ; R0, G0, B0, R1, G1, B1. Can go 1 cycle faster if reversed
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.wrap
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; Note that because the clock edge for pixel n is in the middle of pixel n +
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; 1, a dummy pixel at the end is required to clock the last piece of genuine
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; data. (Also 1 pixel of garbage is clocked out at the start, but this is
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; harmless)
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% c-sdk {
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static inline void hub75_data_rgb888_program_init(PIO pio, uint sm, uint offset, uint rgb_base_pin, uint clock_pin) {
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pio_sm_set_consecutive_pindirs(pio, sm, rgb_base_pin, 6, true);
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pio_sm_set_consecutive_pindirs(pio, sm, clock_pin, 1, true);
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for (uint i = rgb_base_pin; i < rgb_base_pin + 6; ++i)
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pio_gpio_init(pio, i);
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pio_gpio_init(pio, clock_pin);
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pio_sm_config c = hub75_data_rgb888_program_get_default_config(offset);
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sm_config_set_out_pins(&c, rgb_base_pin, 6);
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sm_config_set_sideset_pins(&c, clock_pin);
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sm_config_set_out_shift(&c, true, true, 32);
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// ISR shift to left. R0 ends up at bit 5. We push it up to MSB and then flip the register.
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sm_config_set_in_shift(&c, false, false, 32);
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sm_config_set_fifo_join(&c, PIO_FIFO_JOIN_TX);
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pio_sm_init(pio, sm, offset, &c);
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pio_sm_exec(pio, sm, offset + hub75_data_rgb888_offset_entry_point);
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pio_sm_set_enabled(pio, sm, true);
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}
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// Patch a data program at `offset` to preshift pixels by `shamt`
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static inline void hub75_data_rgb888_set_shift(PIO pio, uint sm, uint offset, uint shamt) {
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uint16_t instr;
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if (shamt == 0)
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instr = pio_encode_pull(false, true); // blocking PULL
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else
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instr = pio_encode_out(pio_null, shamt);
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pio->instr_mem[offset + hub75_data_rgb888_offset_shift0] = instr;
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pio->instr_mem[offset + hub75_data_rgb888_offset_shift1] = instr;
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pio->instr_mem[offset + hub75_data_rgb888_offset_shift2] = instr;
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pio->instr_mem[offset + hub75_data_rgb888_offset_shift3] = instr;
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}
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%}
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