On 09.01.24 14:51, Chuanhong Guo wrote:
Hi!
On Tue, Jan 9, 2024 at 6:52 PM John Crispin <j...@phrozen.org> wrote:
[...]
FAQ
* Why are there are 2 different flash chips?
- the idea is to make the device (almost!) unbrickable and very easy to
recover
What about a built-in JTAG probe instead of SPI-NOR+USB-UART?
It'll be actually unbrickable instead.
- NAND will hold the main loader (U-Boot) and the Linux image and will
be the default boot device
- NOR will be write-protected by default (with WP jumper available on
the board) and will hold a recovery bootloader (and other essential
data, like Wi-Fi calibration)
- a dedicated boot select switch will allow changing between NOR and NAND
[...]
* What is the purpose of the console USB-C port?
- Holtek UART to USB bridge with CDC-ACM support on USB-C makes the
device ultra easy to communicate with. No extra hardware or drivers will
be required. Android for example has CDC-ACM support enabled by default
There are several MCU-based CMSIS-DAP projects out there. They can
provide a CDC-ACM serial with a JTAG interface. It may be a bit slow if a
USB1.1 MCU is picked, but it should be enough to start a bootloader to
unbrick the device.
Here's one with USB2.0 Hi-speed interface:
https://github.com/cherry-embedded/CherryDAP
The Sipeed M0S module used costs 20CNY on Taobao
(or 2.81 USD according to google)
we looked into that kind of solution, i felt more accessible for the
wider audience to use a CDC-ACM chip. flashing using a DAP involves
knowing what JTAG is and how to use it. the idea is that the NOR uboot
has a backup copy of the NAND uboot. holding down one of the buttons
while powering on the device while BOOTSEL is on NOR will auto recover
the NAND. cannot think of a simpler solution. as for the cdc-acm chip.
we looked at the holtek, cypress and microchip components. the holtek
seems to be the easiest to source for the ODM.
John
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