uart txes, now to catch

rp2040_uart/2024-03_rp2040-uart.md

@@ -12,4 +12,23 @@ So, as for reasonable goals for today, I should basically just try to throw-and-
 
 Well actually, fk it, I will use the online pioasm for the time being...
 
-And we're up with a test, I will find the BAUD limit next, and check if that is affected by changes to f_cpu... 
\ No newline at end of file
+And we're up with a test, I will find the BAUD limit next, and check if that is affected by changes to f_cpu... 
+
+This should be simple: we have output is 
+
+```cpp
+float div = (float)clock_get_hz(clk_sys) / (8 * baud);
+```
+
+So we should be able to to clk/8 : 16MBit/s, and indeed we can see things working up to 15MBit/sec. To get to 30, we can crank the CPU to 250MHz. 
+
+| Mbit/s | Traces |
+| --- | --- |
+| 1   | ![img](images/2024-01-03_uart-tx-1mb.png)   |
+| 2.5 | ![img](images/2024-01-03_uart-tx-2p5mb.png) |
+| 10   | ![img](images/2024-01-03_uart-tx-10mb.png)   |
+| 15  | ![img](images/2024-01-03_uart-tx-15mb.png)   |
+| 25  | ![img](images/2024-01-03_uart-tx-25mb.png)   |
+| 30  | ![img](images/2024-01-03_uart-tx-30mb.png)   |
+
+But this is not terribly interesting: we want to see that we can catch words fast enough: the ISR on the RX side is normally where we meet our limits. 
\ No newline at end of file

rp2040_uart/code/uart_pio/uart_pio.ino

@@ -9,7 +9,7 @@
 
 // on XIAO "TX" - GPIO 0 
 #define PIN_TX 0
-#define PIO_BAUD 115200
+#define PIO_BAUD 30000000
 
 // the PIO, and statemachine ? 
 PIO pio = pio0;
@@ -38,6 +38,7 @@ void loop(void){
   digitalWrite(PIN_DEBUG, HIGH);
   // blocking tx-put: 
   uart_tx_program_putc(pio, sm, 85);
+  delayMicroseconds(100);
   digitalWrite(PIN_DEBUG, LOW);
   // ... 
   if(lastUpdate + updateInterval < millis()){