Bootloader Platform Differences

[oclyke]

Intro

Some initial investigation indicates that there may be a dependency on timing of the accompanying Python script on the host computer. On Windows the timing is sufficient to successfully bootload, but on MacOSX (and possibly Linux) the timing causes a failure when using the Artemis Bootloader.

Background

• Most testing of the Artemis Bootloader (also called "SparkFun Variable Loader" or SVL) has occurred on Windows machines.
• Deploying the Apollo3 Arduino Core increased the amount of testing that could be done on Mac and Linux, many thanks to helpful users
• This issue was found after looking into this issue: Upload issue SparkFun Edge

Details

• Differences between Windows and MacOSX (and perhaps Linux) within SVL Python script: (Can be observed in Logic LA captures SecondResetCapture (Mac) and GoodWindowsRef (Windows)
  • Time to switch USB-serial baud rate. (Windows: ~15 ms, MacOSX: ~37 ms)
  • Control lines toggle on change baud rate. (Windows: no control toggle on baud change, MacOSX: Control lines toggle causing another reset after changing baud rate)

Explanation

The differences above cause the bootload process to fail, each for their own reasons.

• The time to switch can cause the bootloader to hang if the computer does not send"BL_COMMAND_COMPUTER_READY" before the bootloader sends "BL_COMMAND_NEXT_FRAME"
• The second reset will wreak havoc on the baud rate negotiation by losing volatile baud rate data.