ReadByte not working in tutorials/SerialMonitor

[William-Purvis]

I've just installed tinygo and tested the blinky and serialmonitor tutorials. The basic serialmonitor code that simply writes "hello World!" works fine, but compiling the more advanced one which accepts keystrokes over the USB port waits for input then simply
types 'p' and then hangs. I've tried putting extra prints in but nothing useful shows up.
A print before the call to ReadByte works - generates a flood of prints until I type something in, then responds with a single 'p' then hangs, no further output.

I'm talking to a waveshare-rp2040-zero.

Any ideas welcome...

[Gustavomurta]

I suggest you test the "echo" examples.
If you have any questions, feel free to ask.
Then let us know the results.

https://github.com/tinygo-org/tinygo/tree/release/src/examples/echo
https://github.com/tinygo-org/tinygo/tree/release/src/examples/echo2

[William-Purvis]

OK, tried both versions. Both behave in same manner as reported above, i.e.: type in a few characters and hit return.
It responds with a single character 'p' then goes dead.
echo2 compiled using 'go' works as I'd expected, i.e.:
$ ./echo2
Echo console enabled. Type something then press enter:
abcdefg
You typed (scanf) : abcdefg
abcdxyz
You typed (scanner) : abcdxyz
^C
Also tried compiling for an Arduino Nano, got the following for both examples:
$ tinygo build -target arduino-nano -serial usb echo2.go
/usr/local/lib/tinygo/src/machine/serial-usb.go:6:12: undefined: Serialer
/usr/local/lib/tinygo/src/machine/serial-usb.go:9:11: undefined: USBCDC

[William-Purvis]

Looking at the first program, if see you are reading the port with ReadBytes(). I have been working with on a different program using network connections to another program and initially tried, this but it reported ReadBytes not declared for net.Conn, only Read() which seems to be equivalent. However, I couldn't get that to work either, and ended up reading the connection in the manner shown in echo2.go, i.e. using bufio.NewScanner. This works, though it seems to inject a zero byte in the first string returned by scanner.Text(). Also it occurs to me that the two echo examples do not specify the line speed, a comment says whatever the default for your device. I've always used 115200 for this with C coding, but explicitly specified. Could this be part of the problem?

[William-Purvis]

Further tests - Arduino-nano complains not enough RAM (hardly a surprise).
SEEED XIAO-RP2040 behaves the same as the waveshare-RP2040-zero.
I don't have any others to try...

[Gustavomurta]

Look how interesting. I'll continue the research later.
Why do I get these control characters repeatedly? (0xD and 0xA)

/*
Raspberry Pico - RP2040 - serial echo test
Gustavo Murta 2025/07/02
tinygo version 0.38.0 windows/amd64 (using go version go1.24.2 and LLVM version 19.1.2)
tinygo flash -target pico main.go
*/

package main

import (
	"fmt"
	"machine"
	"time"
)

func main() {
	machine.Serial.Configure(machine.UARTConfig{}) // init serial usb
        time.Sleep(4 * time.Second)                    // Sleep to catch prints on serial

	println("Type a key(echo via USB):")

	for {
		if machine.Serial.Buffered() > 0 {

			b, err := machine.Serial.ReadByte()
			if err == nil {
				fmt.Printf("Received : 0x%X %c\n", b, b) // print hexadecimal and ASCII
			}
			time.Sleep(250 * time.Millisecond) // timeout 250 ms
		}
	}
}

Type something then press enter:
abcde

ASCII Characters:
0xD = Carriage Return
0xA = Line Feed

Serial Debug Assistant (for Windows) - COM 6 - 115200 Bps 8N1 DTR/RTS

Type a key(echo via USB):
Received : 0xD 
Received : 0xA 

Received : 0x61 a
Received : 0x62 b
Received : 0x63 c
Received : 0x64 d
Received : 0x65 e
Received : 0xD 
Received : 0xA 

Received : 0xD 
Received : 0xA  

Received : 0xD 
Received : 0xA 

Received : 0xD 
Received : 0xA