Hub75: Fix LED ghosting.

drivers/hub75/hub75.cpp

@@ -2,6 +2,8 @@
 #include <algorithm>
 #include <cmath>
 
+#include "hardware/clocks.h"
+
 #include "hub75.hpp"
 
 namespace pimoroni {
@@ -145,6 +147,8 @@ void Hub75::start(irq_handler_t handler) {
             FM6126A_setup();
         }
 
+        uint latch_cycles = clock_get_hz(clk_sys) / 4000000;
+
         // Claim the PIO so we can clean it upon soft restart
         pio_sm_claim(pio, sm_data);
         pio_sm_claim(pio, sm_row);
@@ -156,7 +160,7 @@ void Hub75::start(irq_handler_t handler) {
             row_prog_offs = pio_add_program(pio, &hub75_row_program);
         }
         hub75_data_rgb888_program_init(pio, sm_data, data_prog_offs, DATA_BASE_PIN, pin_clk);
-        hub75_row_program_init(pio, sm_row, row_prog_offs, ROWSEL_BASE_PIN, ROWSEL_N_PINS, pin_stb);
+        hub75_row_program_init(pio, sm_row, row_prog_offs, ROWSEL_BASE_PIN, ROWSEL_N_PINS, pin_stb, latch_cycles);
 
         // Prevent flicker in Python caused by the smaller dataset just blasting through the PIO too quickly
         pio_sm_set_clkdiv(pio, sm_data, width <= 32 ? 2.0f : 1.0f);

drivers/hub75/hub75.pio

@@ -21,7 +21,10 @@
 
 .wrap_target
     out pins, 5 [1]    side 0x2 ; Deassert OEn, output row select
-    out x, 27   [7]    side 0x3 ; Pulse LATCH, get OEn pulse width
+    mov x, y    [3]    side 0x3 ; Pulse LATCH
+wait_loop:
+    jmp x-- wait_loop  side 0x2 ; Wait for row to latch
+    out x, 27          side 0x2 ; Get OEn pulse width
 pulse_loop:
     jmp x-- pulse_loop side 0x0 ; Assert OEn for x+1 cycles
 .wrap
@@ -43,13 +46,16 @@ pulse_loop:
 
 .wrap_target
     out pins, 5 [1]    side 0x3 ; Deassert OEn, output row select
-    out x, 27   [7]    side 0x2 ; Pulse LATCH, get OEn pulse width
+    mov x, y    [3]    side 0x2 ; Pulse LATCH
+wait_loop:
+    jmp x-- wait_loop  side 0x3 ; Wait for row to latch
+    out x, 27          side 0x3 ; Get OEn pulse width
 pulse_loop:
     jmp x-- pulse_loop side 0x1 ; Assert OEn for x+1 cycles
 .wrap
 
 % c-sdk {
-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) {
+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, uint latch_cycles) {
     pio_sm_set_consecutive_pindirs(pio, sm, row_base_pin, n_row_pins, true);
     pio_sm_set_consecutive_pindirs(pio, sm, latch_base_pin, 2, true);
     for (uint i = row_base_pin; i < row_base_pin + n_row_pins; ++i)
@@ -62,6 +68,8 @@ static inline void hub75_row_program_init(PIO pio, uint sm, uint offset, uint ro
     sm_config_set_sideset_pins(&c, latch_base_pin);
     sm_config_set_out_shift(&c, true, true, 32);
     pio_sm_init(pio, sm, offset, &c);
+    pio_sm_exec(pio, sm, pio_encode_out(pio_y, 32));
+    pio_sm_put(pio, sm, latch_cycles);
     pio_sm_set_enabled(pio, sm, true);
 }