measured tft refresh rate see main() for results

.vscode/settings.json

@@ -19,5 +19,5 @@
     "cmake.buildBeforeRun": true,
     "C_Cpp.default.configurationProvider": "ms-vscode.cmake-tools",
     "C_Cpp.errorSquiggles": "disabled",
-    "cortex-debug.variableUseNaturalFormat": false
+    "cortex-debug.variableUseNaturalFormat": true
 }

src/main.c

@@ -47,10 +47,17 @@ int main()
 			tft_fill(0);
 			dma_channel_wait_for_finish_blocking(dma_chan);
 		}
+		tft_start_pixels(lcd_config.pio, lcd_config.sm);
+		absolute_time_t start = get_absolute_time();
 		for(size_t i = 0; i < 8; i++) {
 			tft_fill(31807);
 			dma_channel_wait_for_finish_blocking(dma_chan);
 		}
+		absolute_time_t end = get_absolute_time();
+		volatile int64_t diff = absolute_time_diff_us(start, end);
+		tft_fill(31807);
+		dma_channel_wait_for_finish_blocking(dma_chan);
+		// actual refresh rate ~25hz
 	}
 	return 0;
 }

src/tft.pio

@@ -41,7 +41,7 @@ static inline void tft_program_init(PIO pio, uint sm, uint offset, uint data_pin
 
 // Making use of the narrow store replication behaviour on RP2040 to get the
 // data left-justified (as we are using shift-to-left to get MSB-first serial)
-// => command gets sent 4 times
+// => command gets sent 4 times if out shift is set to 32
 
 static inline void tft_put(PIO pio, uint sm, uint8_t x) {
     while (pio_sm_is_tx_fifo_full(pio, sm))