I2C-Tiny-USB Digispark Reboot Patch

README-patch.md

I2C-Tiny-USB Digispark Reboot Patch

• Tested with I2C-Tiny-USB commit 0a8fa3d. Verified working on Raspberry Pi 3+4. Further test on different devices appreciated.
• Digispark used with RESETDSBL = 0 (see Notes below). Fuses: H:0x5d, L:0xe1, E:0xfe.
• All USB devices directly connected to the Raspberry Pi.
• Apply with patch -l < ....

Notes

1. The Digispark bootloader has been altered to switch into programming mode when PB5 is set to Gnd (Fuse: RESETDSBL =0) insttead of waiting ~3 seconds in programming mode. This repo contains the files needed for the change. (In a nutshell: Enable this line, prepare the "trampolin" with the new bootloader, use an external programmer to set the fuses).
2. For Raspberry Pi 4 only: If you use the I2C-Tiny-USB Digispark on a USB2 port and another USB2 device on a Pi USB3 port this patch does not work. I did not investigate the root cause. Just avoid such combination! All other combinations between Digispark/USB2/USB3 devices worked well and the I2C device showed up automagically after cold boot and warm boot of the Raspberry.

Configurations

Raspberry Pi 3B

Raspbian Debian Buster 10.6: Kernel 5.4.72-v7+

Raspberry Pi 4 (4GB)

Raspbian Debian Buster 10.8: Kernel 5.10.11-v7l+

Firmware:

# rpi-eeprom-update
BCM2711 detected
Dedicated VL805 EEPROM detected
Checking for updates in /lib/firmware/raspberrypi/bootloader/default
Use raspi-config to select either the default-production release or latest update.
BOOTLOADER: up-to-date
CURRENT: Thu  3 Sep 12:11:43 UTC 2020 (1599135103)
 LATEST: Thu  3 Sep 12:11:43 UTC 2020 (1599135103)
RELEASE: default
VL805: up-to-date
CURRENT: 000138a1
 LATEST: 000138a1

digispark_i2c_tiny_usb_reboot.patch

diff --git a/digispark/main.c b/digispark/main.c
index 034a06f..f8eb4e5 100644
--- a/digispark/main.c
+++ b/digispark/main.c
@@ -643,27 +643,22 @@ int main(void) {
 
     // i2c_scan();
 
-    usbDeviceDisconnect();
-    for(i=0;i<20;i++){  /* 300 ms disconnect */
-        _delay_ms(15);
+    cli();
+    usbInit();
+    i = 0;
+    while (--i) { /* fake USB disconnect for > 250 ms */
+        _delay_ms(30);
     }
     usbDeviceConnect();
 
-    wdt_enable(WDTO_1S);
-
-    usbInit();
     sei();
 
 	pinMode(B,1,OUTPUT);
-
-
-
 	pinMode(B,5,INPUT);
 	internalPullup(B,5,DISABLE);
 
     for(;;)
 	{
-        wdt_reset();
         usbPoll();
 	}