Quick Explanation Of Firmware Update Operation (Bootloaders) - Crown XTi series Service Manual

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Quick explanation of firmware update operation (Bootloaders)

There are two sources of non-volatile flash on the CEquel amps.
1. 64kBytes of on-chip flash on U1 the microcontroller. (Program)
2. 2M-bits (256 kBytes) of serial flash U15. (Program and Data Memory)
When firmware is loaded via RS-232, it uses a very low level bootloader on the microcontroller and only
the on-chip flash is reprogrammed. The serial flash is not changed.
When firmware is loaded via USB, it uses a high level bootloader written by me and it runs in RAM. It
follows this sequence of events.
1. Start receiving the firmware download packets via USB
2. After 256-bytes (1-page) have been received, program that page in serial flash.
3. After the serial flash has been completely reprogrammed, the download is finished
4. Set the reboot flag in serial flash.
5. Load the bootloader from on-chip flash to RAM and jump to it.
6. Erase the entire on-chip flash
7. Program the on-chip flash with the data stored in Sector 3 of serial flash
8. When finished clear the reboot flag and go to an infinite loop and wait for the watchdog to time out
and reboot.
You can see the the most critical steps are 5 and 6. This is the only place you can really screw things up.
If something goes wrong in steps 5 or 6 and they can not complete, you will have to reprogram the micro
using the RS-232 method.
Notice in step 4 a reboot flag is set, this was implemented because the current firmware update utility in
System Architect can NOT guarantee a reboot command will be sent and thus a complete firmware
update. The reboot flag is only cleared after the micro on-chip flash has been successfully reprogrammed.
This flag is checked at every power up. If it is set, the bootloader will be called.
If a USB download is interrupted, it should not cause any fatal problems. I will simply leave the serial flash
in some undefined state. The micro should boot-up normally. However, the DSP program and parameter
can be corrupted causing serious problems (although most likely it will not pass audio). Also the LCD will
most likely appear to look corrupted, because any LCD segment can be on or off given bogus data in
serial flash. Most importantly, the micro should run and another USB firmware download can be
attempted.
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CEquel Digital Systems Overview
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