start uart

rpi_uart/2023-12-29_rpi-serial-rates.md

+## 2023 12 29
+
+So, spinning this up is pretty simple (on the pi 4) we use the configuration tool (UI version actually shows the options we want, command line version misses one) to set UART and SPI interfaces available, then the test code is just using pyserial:
+
+```python
+import serial, time 
+
+baud = 2000000
+
+print(f'bit time should be {1000000/baud}us')
+
+ser = serial.Serial('/dev/serial0', baud)
+
+for i in range(10000):
+    ser.write(bytearray([95]))
+    time.sleep(0.001)
+
+ser.close() 
+```
+
+Now, I'm trying to figure where the limit is, so, baud values and measured bit times:
+
+| Baud Setting | Expected Bit Time | Measured | Match |
+| --- | --- | --- | --- | 
+| 115200 | 8.681us | 8.703us | 0.997 |
+| 1000000 | 1.0us | 1.024us | 0.977 |
+| 2000000 | 500ns | 512ns | 0.977 |
+| 3000000 | 333ns | 352ns | 0.946 |
+| 4000000 | 250ns | 271ns | 0.922 |
+| 5000000 | 200ns | 223ns | 0.923 |
+| 6000000 | 166ns | 176ns | 0.943 |
+| 10000000 | 100ns | 111ns | 0.901 |
+
+So we can actually get up to ~ 5MBit/sec and (nearly) survive, though baud settings might need to be trimmed on a scope to get-robust. This is a pretty good sign, and it means we can probably make a serviceable link using UART, though we might end up wanting to deploy two. I'll see quickly about the SPI speeds and then try to figure out where to push. 
\ No newline at end of file

rpi_uart/code/pi_uart.py

+import serial, time 
+
+baud = 10000000
+
+print(f'bit time should be {1000000/baud}us')
+
+ser = serial.Serial('/dev/serial0', baud)
+
+for i in range(10000):
+    ser.write(bytearray([95]))
+    time.sleep(0.001)
+
+ser.close() 
\ No newline at end of file

rpi_uart/code/serial_list.py

+import serial.tools.list_ports
+
+def list_serial_ports():
+    ports = serial.tools.list_ports.comports()
+    print(f"Total Ports: {len(ports)}")
+    for port in ports:
+        print(f"Port: {port.device}")
+        print(f" - Description: {port.description}")
+        if port.serial_number:
+            print(f" - Serial Number: {port.serial_number}")
+        if port.manufacturer:
+            print(f" - Manufacturer: {port.manufacturer}")
+        if port.product:
+            print(f" - Product: {port.product}")
+        if port.vid is not None:
+            print(f" - VID: {port.vid:04X}")
+        if port.pid is not None:
+            print(f" - PID: {port.pid:04X}")
+        print()
+
+list_serial_ports()