I've figured out how to do this. In short, you must send a "Feature Report" consisting of the bytes 0x9, 0x0, 0x0, 0x0 to the appropriate hidraw device as root.
You can find the right hidraw device with this command:
dmesg | grep Apple | grep Keyboard | grep input0 | tail -1 | sed -e 's/.*hidraw\([[:digit:]]\+\).*/\/dev\/hidraw\1/'
The code to send the magic control packet is below. Compiles with gcc, takes the hidraw device as parameter. So the entire flow is:
- save the code below as
disable-capslock-delay.c
gcc -o disable-capslock-delay disable-capslock-delay.cHIDDEVICE=$(dmesg | grep Apple | grep Keyboard | grep input0 | tail -1 | sed -e 's/.*hidraw\([[:digit:]]\+\).*/\/dev\/hidraw\1/')sudo ./disable-capslock-delay $HIDDEVICE
Steps 3 and 4 have to be done every time you reboot (or unplug and re-plug the keyboard); you can put them into /etc/rc.local (or your distro's equivalent) to execute them at boot (you don't need sudo in that case; and you might want to move the compiled binary into /usr/local/sbin/ or something).
I've put in some safety checks for vendor ID, device ID, and report descriptor length. You may have to change the latter two if your model differs from mine.
#include <linux/hidraw.h>
#include <sys/ioctl.h>
#include <fcntl.h>
#include <stdio.h>
#include <string.h>
int main(int argc, char **argv) {
if (argc != 2 || strcmp(argv[1], "-h") == 0) {
printf("Pass a hidraw device as the first and only parameter!\n");
printf("You may find the right device with:\n");
printf(" dmesg | grep Apple | grep Keyboard | grep input0 | tail -1 | "
"sed -e 's/.hidraw\([[:digit:]]\+\)./\/dev\/hidraw\1/'\n");
return 1;
}
int fd, i, res, desc_size = 0;
char buf[256];
struct hidraw_devinfo info;
char *device = argv[1];
fd = open(device, O_RDWR | O_NONBLOCK);
if (fd < 0) {
perror("Unable to open device");
return 1;
}
memset(&info, 0, sizeof(info));
memset(buf, 0, sizeof(buf));
// Get Report Descriptor Size
res = ioctl(fd, HIDIOCGRDESCSIZE, &desc_size);
if (res < 0) {
perror("HIDIOCGRDESCSIZE");
}
if (desc_size != 75) {
printf("Error: unexpected descriptor size %d; you've probably got "
"the wrong hidraw device!\n", desc_size);
return 1;
}
// Get Raw Info
res = ioctl(fd, HIDIOCGRAWINFO, &info);
if (res < 0) {
perror("HIDIOCGRAWINFO");
} else {
if (info.vendor != 0x05ac) {
printf("Error: Wrong vendor ID, make sure you got the right "
"hidraw device!\n");
return 1;
}
if (info.product != 0x0250) {
printf("Warning: Unknown product ID 0x%x!\n", info.product);
}
}
// Get Feature
buf[0] = 0x09; // Report Number
res = ioctl(fd, HIDIOCGFEATURE(256), buf);
if (res < 0) {
perror("HIDIOCGFEATURE");
} else {
printf("HID Feature Report (before change):\n\t");
for (i = 0; i < res; i++) printf("%hhx ", buf[i]);
puts("\n");
}
// Set Feature
buf[0] = 0x09; // Report Number
buf[1] = 0x00; // Report data
buf[2] = 0x00; // padding
buf[3] = 0x00; // padding
res = ioctl(fd, HIDIOCSFEATURE(4), buf);
if (res < 0) {
perror("HIDIOCSFEATURE");
} else {
printf("Caps lock delay disabled.\n");
}
// Get Feature
buf[0] = 0x09; // Report Number
res = ioctl(fd, HIDIOCGFEATURE(256), buf);
if (res < 0) {
perror("HIDIOCGFEATURE");
} else {
printf("HID Feature Report (after change):\n\t");
for (i = 0; i < res; i++) printf("%hhx ", buf[i]);
puts("\n");
}
close(fd);
return 0;
}
