Pi 400 KB

README.md

Raspberry Pi 400 as a USB HID Keyboard

Hook your Pi 400 up to your PC somehow, using a USB Type-C cable into the power port. Anker make good ones- I used a 3m white one for my tests.

Setup

Add dtoverlay=dwc2 to /boot/config.txt

Reboot!

Clone libusbgx somewhere and build according INSTALL, including "sudo make install"
https://github.com/linux-usb-gadgets/libusbgx

Run sudo modprobe libcomposite

Run make

Run sudo ./pi400

YOUR PI 400 IS NOW A FREAKING KEYBOARD FOR YOUR PC WHAAAAT!?

Your keyboard input will be detached from your Pi while it's forwarded to your host computer.

Press Ctrl + Raspberry to exit and restore your keyboard on the Pi.

I did copy self-built "pi400" to "/usr/local/bin" and use now "laptop" alias for using Pi400 as laptop keyboard:

pi@raspberrypi400:~ $ tail -1 ~/.bashrc
alias laptop="sudo pi400 2>/dev/null >/dev/null"
pi@raspberrypi400:~ $ 

gadget-hid.c

#include "gadget-hid.h"
#include <errno.h>
#include <stdio.h>
#include <usbg/function/midi.h>

static char report_desc[] = {
	0x05, 0x01,
	0x09, 0x06,
	0xA1, 0x01,
	0x05, 0x07,
	0x19, 0xe0,
	0x29, 0xe7,
	0x15, 0x00,
	0x25, 0x01,

	0x75, 0x01,
	0x95, 0x08,
	0x81, 0x02,
	0x95, 0x01,
	0x75, 0x08,
	0x81, 0x01,
	0x95, 0x03,
	0x75, 0x01,

	0x05, 0x08,
	0x19, 0x01,
	0x29, 0x03,
	0x91, 0x02,
	0x95, 0x05,
	0x75, 0x01,
	0x91, 0x01,
	0x95, 0x06,

	0x75, 0x08,
	0x15, 0x00,
	0x26, 0xff,
	0x00, 0x05,
	0x07, 0x19,
	0x00, 0x2a,
	0xff, 0x00,
	0x81, 0x00, // Input (Data, Array, Abs)
	0xc0 // End collection
};

int initUSB() {
    int ret = -EINVAL;
    int usbg_ret;

    struct usbg_gadget_attrs g_attrs = {
        .bcdUSB = 0x0200,
        .bDeviceClass = USB_CLASS_PER_INTERFACE,
        .bDeviceSubClass = 0x00,
        .bDeviceProtocol = 0x00,
        .bMaxPacketSize0 = 64, /* Max allowed ep0 packet size */
        .idVendor = VENDOR,
        .idProduct = PRODUCT,
        .bcdDevice = 0x0001, /* Verson of device */
    };

    struct usbg_gadget_strs g_strs = {
        .serial = "0123456789", /* Serial number */
        .manufacturer = "Pimoroni", /* Manufacturer */
        .product = "Keybow" /* Product string */
    };

    struct usbg_config_strs c_strs = {
        .configuration = "1xHID"
    };

    struct usbg_f_midi_attrs midi_attrs = {
        .index = 1,
        .id = "usb1",
        .buflen = 128,
        .qlen = 16,
        .in_ports = 1,
        .out_ports = 1
    };

    struct usbg_f_hid_attrs f_attrs = {
        .protocol = 1,
        .report_desc = {
            .desc = report_desc,
            .len = sizeof(report_desc),
        },
        .report_length = 16,
        .subclass = 0,
    };

    usbg_ret = usbg_init("/sys/kernel/config", &s);
    if (usbg_ret != USBG_SUCCESS) {
        fprintf(stderr, "Error on usbg init\n");
        fprintf(stderr, "Error: %s : %s\n", usbg_error_name(usbg_ret),
                usbg_strerror(usbg_ret));
        goto out1;
    }

    usbg_ret = usbg_create_gadget(s, "g1", &g_attrs, &g_strs, &g);
    if (usbg_ret != USBG_SUCCESS) {
        fprintf(stderr, "Error creating gadget\n");
        fprintf(stderr, "Error: %s : %s\n", usbg_error_name(usbg_ret),
                usbg_strerror(usbg_ret));
        goto out2;
    }

    usbg_ret = usbg_create_function(g, USBG_F_HID, "usb0", &f_attrs, &f_hid);
    if (usbg_ret != USBG_SUCCESS) {
        fprintf(stderr, "Error creating function: USBG_F_HID\n");
        fprintf(stderr, "Error: %s : %s\n", usbg_error_name(usbg_ret),
                usbg_strerror(usbg_ret));
        goto out2;
    }

    usbg_ret = usbg_create_config(g, 1, "config", NULL, &c_strs, &c);
    if (usbg_ret != USBG_SUCCESS) {
        fprintf(stderr, "Error creating config\n");
        fprintf(stderr, "Error: %s : %s\n", usbg_error_name(usbg_ret),
                usbg_strerror(usbg_ret));
        goto out2;
    }

    usbg_ret = usbg_add_config_function(c, "keyboard", f_hid);
    if (usbg_ret != USBG_SUCCESS) {
        fprintf(stderr, "Error adding function: keyboard\n");
        fprintf(stderr, "Error: %s : %s\n", usbg_error_name(usbg_ret),
                usbg_strerror(usbg_ret));
        goto out2;
    }

    usbg_ret = usbg_enable_gadget(g, DEFAULT_UDC);
    if (usbg_ret != USBG_SUCCESS) {
        fprintf(stderr, "Error enabling gadget\n");
        fprintf(stderr, "Error: %s : %s\n", usbg_error_name(usbg_ret),
                usbg_strerror(usbg_ret));
        goto out2;
    }

    ret = 0;

out2:
    usbg_cleanup(s);
    s = NULL;

out1:
    return ret;
}

int cleanupUSB(){
    if(g){
        usbg_disable_gadget(g);
        usbg_rm_gadget(g, USBG_RM_RECURSE);
    }
    if(s){
        usbg_cleanup(s);
    }
    return 0;
}

gadget-hid.h

#include <linux/usb/ch9.h>
#include <usbg/usbg.h>
#include <usbg/function/hid.h>

#define VENDOR          0x04d9
#define PRODUCT         0x0007
#define HID_REPORT_SIZE 8

usbg_state *s;
usbg_gadget *g;
usbg_config *c;
usbg_function *f_hid;

int initUSB();
int cleanupUSB();

Makefile

pi400: CFLAGS+=-static -lusbgx -lconfig -DPI400_USB
pi400: pi400.c gadget-hid.c
	$(CC)  $^ $(CFLAGS) -o $@

clean:
	-rm pi400

pi400.c

#include "pi400.h"

#include "gadget-hid.h"

#include <sys/ioctl.h>
#include <linux/hidraw.h>
#include <linux/input.h>
#include <signal.h>
#include <errno.h>
#include <stdio.h>
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>


#define KEYBOARD_DEV "/dev/input/by-id/usb-_Raspberry_Pi_Internal_Keyboard-event-kbd"

#define HID_REPORT_SIZE 8
#define GRAB 1
#define UNGRAB 0

int hid_output;
volatile int running = 0;
int key_index = 0;

void signal_handler(int dummy) {
    running = 0;
}

int find_hidraw_device() {
    int fd;
    int ret;
    struct hidraw_devinfo hidinfo;
    char path[20];

    for(int x = 0; x < 16; x++){
	sprintf(path, "/dev/hidraw%d", x);
        if ((fd = open(path, O_RDWR | O_NONBLOCK)) == -1) {
            continue;
        }

        ret = ioctl(fd, HIDIOCGRAWINFO, &hidinfo);

        if(hidinfo.vendor == VENDOR && hidinfo.product == PRODUCT) {
	    printf("Found keyboard at: %s\n", path);
	    return fd;
        }

	close(fd);
    }

    return -1;
}

int main() {
    int ret;
    int fd;
    int uinput_fd;
    unsigned char buf[HID_REPORT_SIZE];

    fd = find_hidraw_device();
    if(fd == -1) {
	printf("Failed to open keyboard device\n");
	return 1;
    }
    ret = initUSB();

    uinput_fd = open(KEYBOARD_DEV, O_RDONLY);
    ioctl(uinput_fd, EVIOCGRAB, UNGRAB);
    usleep(500000);
    ioctl(uinput_fd, EVIOCGRAB, GRAB);

    do {
        hid_output = open("/dev/hidg0", O_WRONLY | O_NDELAY);
    } while (hid_output == -1 && errno == EINTR);
    if (hid_output == -1){
        printf("Error opening /dev/hidg0 for writing.\n");
        return 1;
    }

    printf("Running...\n");
    running = 1;
    signal(SIGINT, signal_handler);

    while (running){
	int c = read(fd, buf, HID_REPORT_SIZE);
	if(c != HID_REPORT_SIZE){
		continue;
	}
	for(int x = 0; x < HID_REPORT_SIZE; x++)
	{
		printf("%x ", buf[x]);
	}
	printf("\n");
	write(hid_output, buf, HID_REPORT_SIZE);
        usleep(1000);

	if(buf[0] == 0x09){
	    running = 0;
	    break;
	}
    } 

    for(int x = 0; x < HID_REPORT_SIZE; x++){
	buf[x] = 0;
    };

    write(hid_output, buf, HID_REPORT_SIZE);

    ioctl(uinput_fd, EVIOCGRAB, UNGRAB);
    close(uinput_fd);

    printf("Cleanup USB\n");
    cleanupUSB();

    return 0;
}

pi400.h

#include <pthread.h>

int initUSB();
int main();
void sendHIDReport();