Org on Github
# ==========================================================
PICO_SDK_FETCH_FROM_GIT=1 PICO_EXTRAS_FETCH_FROM_GIT=1 cmake -DCMAKE_TOOLCHAIN_FILE=../pico_arm_gcc_toolchain.cmake .. -DCMAKE_C_FLAGS="-mcpu=cortex-m0plus -mthumb"  -DCMAKE_CXX_FLAGS="-mcpu=cortex-m0plus -mthumb" -DCMAKE_ASM_FLAGS="-mcpu=cortex-m0plus -mthumb"

compile here:
# ==========================================================
PICO_SDK_FETCH_FROM_GIT=1 PICO_EXTRAS_FETCH_FROM_GIT=1 cmake -DCMAKE_TOOLCHAIN_FILE=/home/pi/pico/pico-sdk/cmake/preload/toolchains/pico_arm_cortex_m0plus_gcc.cmake .. -DCMAKE_C_FLAGS="-mcpu=cortex-m0plus -mthumb"  -DCMAKE_CXX_FLAGS="-mcpu=cortex-m0plus -mthumb" -DCMAKE_ASM_FLAGS="-mcpu=cortex-m0plus -mthumb"

cp ../../pico-sdk/external/pico_sdk_import.cmake .


CMakeLists.txt Line 59

from
# ==========================================================
pico_enable_stdio_usb(${PROJECT} 1)  # Enable USB serial
pico_enable_stdio_uart(${PROJECT} 0) # Disable UART serial
# ==========================================================

to
# ==========================================================
# Enable USB and UART output
# pico_enable_stdio_usb(${PROJECT} 0)  # Disable USB serial
pico_enable_stdio_usb(${PROJECT} 1)  # Enable USB  serial
pico_enable_stdio_uart(${PROJECT} 1) # Enable UART serial
# ==========================================================


Edit main.c Header - includes and defining UART
# ==========================================================
#include <stdio.h>
#include <string.h>
#include "pico/stdlib.h"
#include "pico/audio_pwm.h"
#include "pico/stdio_usb.h"
#include "hardware/uart.h"
#include "hardware/gpio.h"
#include "hardware/clocks.h"


#include "epsonapi.h" // import DECtalk 4.99

// https://raw.githubusercontent.com/raspberrypi/pico-examples/refs/heads/master/uart/uart_advanced/uart_advanced.c

// Define UART
#define UART_ID uart0
#define BAUD_RATE 9600
#define DATA_BITS 8
#define STOP_BITS 1
#define PARITY    UART_PARITY_NONE

// We are using pins 0 and 1, but see the GPIO function select table in the
// datasheet for information on which other pins can be used.
#define UART_TX_PIN 0
#define UART_RX_PIN 1

...

char inbuf[2048];
static int chars_rxed = 0;

// RX interrupt handler
void on_uart_rx() {
    while (uart_is_readable(UART_ID)) {
        uint8_t ch = uart_getc(UART_ID);
        // Can we send it back?
        if (uart_is_writable(UART_ID)) {
            // Change it slightly first!
            ch++;
            uart_putc(UART_ID, ch);
        }
        chars_rxed++;
    }
}


int main() {


...

    // Now init USB serial at the correct clock speed
    stdio_init_all();

    // Set up our UART
    uart_init(UART_ID, BAUD_RATE);

    // Set the TX and RX pins by using the function select on the GPIO
    // Set datasheet for more information on function select
    gpio_set_function(UART_TX_PIN, UART_FUNCSEL_NUM(UART_ID, UART_TX_PIN));
    gpio_set_function(UART_RX_PIN, UART_FUNCSEL_NUM(UART_ID, UART_RX_PIN));

    // Set our data format
    uart_set_format(UART_ID, DATA_BITS, STOP_BITS, PARITY);

	// Enable FIFO
    uart_set_fifo_enabled(UART_ID, true);
	
    // Set up a RX interrupt
    // We need to set up the handler first
    // Select correct interrupt for the UART we are using
    int UART_IRQ = UART_ID == uart0 ? UART0_IRQ : UART1_IRQ;

    // And set up and enable the interrupt handlers
    irq_set_exclusive_handler(UART_IRQ, on_uart_rx);
    irq_set_enabled(UART_IRQ, true);

    // Now enable the UART to send interrupts - RX only
    uart_set_irq_enables(UART_ID, true, false);



# ==========================================================


su pi
export PICO_SDK_PATH=/home/pi/pico/pico-sdk

cd /home/pi/
# mkdir pico
cd pico
git clone https://github.com/dectalk/DECtalkMini.git dectalkmini
cd dectalkmini/pico
cp ../../pico-sdk/external/pico_sdk_import.cmake .
export PICO_SDK_PATH=/home/pi/pico/pico-sdk
nano  CMakeLists.txt
nano main.c
mkdir build
cd build
# OLD:PICO_SDK_FETCH_FROM_GIT=1 PICO_EXTRAS_FETCH_FROM_GIT=1 cmake -DCMAKE_TOOLCHAIN_FILE=/home/pi/pico/pico-sdk/cmake/preload/toolchains/pico_arm_cortex_m0plus_gcc.cmake .. -DCMAKE_C_FLAGS="-mcpu=cortex-m0plus -mthumb"  -DCMAKE_CXX_FLAGS="-mcpu=cortex-m0plus -mthumb" -DCMAKE_ASM_FLAGS="-mcpu=cortex-m0plus -mthumb"
PICO_SDK_FETCH_FROM_GIT=1 PICO_EXTRAS_FETCH_FROM_GIT=1 cmake .. -DCMAKE_C_FLAGS="-mcpu=cortex-m0plus -mthumb"  -DCMAKE_CXX_FLAGS="-mcpu=cortex-m0plus -mthumb" -DCMAKE_ASM_FLAGS="-mcpu=cortex-m0plus -mthumb"
make -j$(nproc)





# ==========================================================
# ==========================================================


mkdir build

cd build

PICO_SDK_FETCH_FROM_GIT=1 PICO_EXTRAS_FETCH_FROM_GIT=1 cmake -DCMAKE_TOOLCHAIN_FILE=/home/pi/pico/pico-sdk/cmake/preload/toolchains/pico_arm_cortex_m0plus_gcc.cmake .. -DCMAKE_C_FLAGS="-mcpu=cortex-m0plus -mthumb"  -DCMAKE_CXX_FLAGS="-mcpu=cortex-m0plus -mthumb" -DCMAKE_ASM_FLAGS="-mcpu=cortex-m0plus -mthumb"

make -j$(nproc)



PICO_SDK_FETCH_FROM_GIT=1 
PICO_EXTRAS_FETCH_FROM_GIT=1 
cmake -DCMAKE_TOOLCHAIN_FILE=../pico_arm_gcc_toolchain.cmake .. 
-DCMAKE_C_FLAGS="-mcpu=cortex-m0plus -mthumb"  
-DCMAKE_CXX_FLAGS="-mcpu=cortex-m0plus -mthumb" 
-DCMAKE_ASM_FLAGS="-mcpu=cortex-m0plus -mthumb"