ESP32-PICO-V3

[alecamaracm]

Hello, we are transitioning a design from a ESP32-WROOM to a PICO-V3.
Unfortunatelly, when trying to program the new custom board with the PICO-V3, the flashing procedure fails half way through.

When starting the ESP in the normal way, this is outputted from the UART port:

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rst:0x10 (RTCWDT_RTC_RESET),boot:0x1f (SPI_FAST_FLASH_BOOT)
invalid header: 0xffffffff
invalid header: 0xffffffff
invalid header: 0xffffffff
...

Based on the bootstrap pin register, the bootstrap configuration seems to be fine (All high but GPIO12), and the "invalid header:0xfffffff" agrees with an empty FLASH, so all good here.

When trying to flash new code, it gets a timeout mid way thorugh the process:

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TRACE +0.000 Write 171 bytes:
    c00011a000720000 0090000000000000 | .....r..........
    0000000000000000 0078da5b15dbdcc8 | .........x.[....
    c430818181218081 21afac98011dac0a | .0...!..!.......
    6064607800642830 30e49724a6249624 | `d`x.d(00..$.$.$
    a2c93308303000d5 3088302416141860 | ..3.00..0.0$...`
    ea671064601085c9 1b62317f26038326 | .g.d`....b1.&..&
    03c894d4d482a2fc 5c0cf9260601a0fc | ........\..&....
    073186e282ccb434 3427be7efd1f055c | .1.....44'.~...\
    779150cfe638b964 ddae9f6f23ac4f4c | w.P..8.d...o#.OL
    fb3f0a46c1281805 a360148c8251300a | .?.F.(...`...Q0.
    46c128800300fb17 44a6c0           | F.(.....D..
TRACE +0.018 Read 1 bytes: c0
TRACE +0.000 Read 11 bytes: 01110200000000000000c0
TRACE +0.001 Received full packet: 01110200000000000000
TRACE +0.001 command op=0x0a data len=4 wait_response=1 timeout=3.000 data=00100040
TRACE +0.000 Write 14 bytes: c0000a04000000000000100040c0
TRACE +3.014 Timed out waiting for packet header

A fatal error occurred: Timed out waiting for packet header

Full log here: https://pastebin.com/KtpmAmRJ

Based on this log, it seems like the UART communication (we are using a CP2102N USB-UART) works as expected.
My best guess is that when the PICO-V3 is used, a special flash configuration needs to be set, but we have been playing with it for a while and we have had no success.

Any idea on why that might be happening?

[ESP_Sprite]

Are you sure you don't have anything connected to the Pico's flash GPIOs? Note that these pins are different from
'normal' ESP32 flash pins.

[alecamaracm]

Hello, these pins have been left unconnected:
- IO6 (31) (CLK)
- IO7 (32) (SD0)
- IO8 (33) (SD1)
- IO9 (28) (SD2)
- IO10 (29) (SD3)
- IO11 (30) (CMD)

The datasheet also mentions IO16 and IO17 but those are not exposed in the PICO-V3 package.
Is there any other FLASH pin that we are missing?

[WiFive]

Gpio 6 and 11 are the only pins that need to be avoided on pico v3

[alecamaracm]

Those pins are not connected to anything else.
Any ideas on what else might be going wrong?

[ESP_Sprite]

Nothing I can quickly spot... what you see seems to be congruent with an inability to talk to flash, but if you have everything connected like you say you have, it should just work. Have you tried multiple prototypes? Perhaps you're just seeing the results of a solder bridge or something?

[alecamaracm]

Hello, I just noticed we don't have the 10uF decoupling capacitor that is present in the "ESP32-PICO-KIT V3" schematic 3.3V rail.
We weren't going to use WIFI/BL at all so we ended up removing it to save board space.
Do you think that could be the reason the upload fails?

[ESP_Sprite]

Doesn't seem likely, but it may be worth re-soldering it to see if it solves the issue. (In general, what's your power supply situation like btw?)

[alecamaracm]

We got around 10 of them assembled and none of them work, so that doesn't seem to be the problem.
For the power supply, we are just using a 3V3 LDO (XC6206P332MR) which should be more than enough for this application.
About the exposed flash pins, as can be seen in this picture, they all are literally unconnected and they are even surrounded by also non-connected pins.

We also changed the USB-UART chip but communication seems fine before the upload.

[WiFive]

Can you read the whole flash? Can you write the whole flash in smaller chunks? Have you tried different baud rates? Different computers? Latest version of esptool?