I am working on a pet project that has both an SPI NOR flash (for bootloader) and eMMC (OS image).
For SPI NOR I will provide a small connector to interface directly into it.
Now, since I have never used eMMC in projects I do not know the best/standard approach on this.
I see two options:
- Write initial image before soldering eMMC. I will be using an assembly service, so I need to find one that will do this for me.
- Provide in-circuit interface for writing an eMMC. Perhaps something like JTAG-UART-sized pin connector which will interface into eMMC directly, so I can write it without bringing up the entire board.
Now as far as I know, in bulk manufacturing the first option is used. However, I do not know how reliable it is. If the eMMC will be heated to over 200C, wouldn't that potentially damage the data already written on it?
Also, I think that in the second approach it is easier to rescue the board if I do something wrong.
So my question is - which is the standard approach? Maybe I am missing a 3rd option?
PS: I've checked a few development boards that I have and all of them come with JTAG/UART connectors, but I actually never used them for anything other than troubleshooting boot of the board. Is it possible to write eMMC over those connectors without making a new non-standard one? How is it done usually?