AVRDUDE: Troubleshooting

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# B. Troubleshooting

In general, please report any bugs encountered via
http://savannah.nongnu.org/bugs/?group=avrdude.

- Problem: I'm using a serial programmer under Windows and get the following error:

  `avrdude: serial_open(): can't set attributes for device "com1"`,

  Solution: This problem seems to appear with certain versions of Cygwin. Specifying `"/dev/com1"` instead of `"com1"` should help.

- Problem: I'm using linux and my AVR910 programmer is really slow.

  Solution (short): `setserial port low_latency`

  Solution (long): There are two problems here. First, the system may wait some time before it passes data from the serial port to the program. Under Linux the following command works around this (you may need root privileges for this).

  `setserial port low_latency`

  Secondly, the serial interface chip may delay the interrupt for some time. This behaviour can be changed by setting the FIFO-threshold to one. Under Linux this can only be done by changing the kernel source in `drivers/char/serial.c`. Search the file for `UART_FCR_TRIGGER_8` and replace it with `UART_FCR_TRIGGER_1`. Note that overall performance might suffer if there is high throughput on serial lines. Also note that you are modifying the kernel at your own risk.

- Problem: I'm not using linux and my AVR910 programmer is really slow.

  Solutions: The reasons for this are the same as above. If you know how to work around this on your OS, please let us know.

- Problem: AVRDUDE says my device is not supported when using the AVR109 boot loader

  Solution: Currently, AVRDUDE uses the AVR910 device codes given in the `avrdude.conf` file, and matches them against the list of supported devices reported by the programmer. Unfortunately, there are no device codes at all for some of the newer AVR devices, and even worse, the device codes listed in `preprocessor.xls` of appnote AVR109 do not match those once specified in AVR910.

  Use the -F option to force AVRDUDE to continue anyway.

- Problem: Updating the flash ROM from terminal mode does not work with the JTAG ICEs.

  Solution: None at this time. Currently, the JTAG ICE code cannot write to the flash ROM one byte at a time.

- Problem: Page-mode programming the EEPROM (using the -U option) does not erase EEPROM cells before writing, and thus cannot overwrite any previous value != 0xff.

  Solution: None. This is an inherent feature of the way JTAG EEPROM programming works, and is documented that way in the Atmel AVR datasheets. In order to successfully program the EEPROM that way, a prior chip erase (with the EESAVE fuse unprogrammed) is required.

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