Forums - GPIO20_BE in QCA4020 DVK

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GPIO20_BE in QCA4020 DVK
Join Date: 24 Nov 20
Posts: 4
Posted: Sat, 2021-05-08 01:52

Hello expert,

I am using the QCA4020 DVK to flash the "Hello World" application to the M20 module. According to the steps here, J31 (or GPIO20_BE as inthe schematic of the DVK) force the DVK into the JTAG mode.
Hello World w/ QCA4020 Dev Kit - Qualcomm Developer Network

y question is that in the QCA4020 or M20 documentations, there is no indication that GPIO20_BE can be used for forcing JTAG mode?. Or may be I am not reading it well in the documentation. Can you please help where in the documentaiton it mention that GPIO20_BE is used for forcing JTAG mode?

Thanks a lot!

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Join Date: 18 Jun 18
Location: San Jose
Posts: 317
Posted: Mon, 2021-05-10 10:42

Kindly refer to QCA402x Programmers Guide 80-Y9381-2 Rev. K Section A.3.12 JTAG debug GPIO bootstrap configuration

"The debug mode using JTAG depends upon a JTAG debug GPIO bootstrap. This GPIO is kept high during debug which helps the firmware to wait (in a while loop) for JTAG to connect. GPIO20 is used for the JTAG debug mode by default. In case GPIO20 is used for some other purpose and is kept high, the device goes in to a waiting loop for JTAG and does not boot."

QCA402x (CDB2x) Development Kit User Guide 80-YA121-140 Rev. E Section 2.6.1 Flash the image using JTAG
"Connect the jumper on J31 1&2 in the CDB2x board. After flashing through JTAG is done, remove the jumper."

Table A-1 CDB20 customer development board jumper settings

"J31 = For autoboot mode, remove jumper / For JTAG debug/flashing, connect pins 1 and 2 "

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