Sorry, I lost part of my posting. Here is the correct submission.
I purchased a "broken" R6900 that someone installed openwrt on. They sold it for "parts". Because it was cheap, I figured i'd give it a try.
After installing the stock software, I did a reset and that's when the problems started. When left to boot, it goes around and around. I carefully checked for tftp opportunities but didnt respond to pings at all (didnt realize at that time that the link was down.)
I connected a TTL to USB device and connected to the system's console. There I discovered uboot and tried (in vain) to use tftp.
Knowing nothing about uboot, my research made me realize, after doing a printenv, that more variables needed to be defined. I tried setenv several times but the system refused to save them. Indeed, it deleted them. Is this related to the NAND problems?
Here's the output from power on to playing with uboot
===================================================================
MT7621 stage1 code Mar 12 2015 14:42:52 (ASIC)
CPU=50000000 HZ BUS=16666666 HZ
==================================================================
Change MPLL source from XTAL to CR...
do MEMPLL setting..
MEMPLL Config : 0x11100000
3PLL mode + External loopback
=== XTAL-40Mhz === DDR-1200Mhz ===
PLL4 FB_DL: 0x7, 1/0 = 644/380 1D000000
PLL3 FB_DL: 0xa, 1/0 = 667/357 29000000
PLL2 FB_DL: 0x12, 1/0 = 625/399 49000000
do DDR setting..[00320381]
Apply DDR3 Setting...(use customer AC)
0 8 16 24 32 40 48 56 64 72 80 88 96 104 112 120
--------------------------------------------------------------------------------
0000:| 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0001:| 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0002:| 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0003:| 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0004:| 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0005:| 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0006:| 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0007:| 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0008:| 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0009:| 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
000A:| 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
000B:| 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
000C:| 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
000D:| 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
000E:| 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1
000F:| 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 0
0010:| 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0
0011:| 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0
0012:| 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0013:| 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0014:| 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0015:| 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0016:| 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0017:| 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0018:| 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0019:| 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
001A:| 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
001B:| 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
001C:| 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
001D:| 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
001E:| 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
001F:| 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
DRAMC_DQSCTL1[0e0]=14000000
DRAMC_DQSGCTL[124]=80000000
rank 0 coarse = 16
rank 0 fine = 40
B:| 0 0 0 0 0 0 0 0 1 1 1 0 0 0 0 0
opt_dle value:9
DRAMC_DDR2CTL[07c]=C287221D
DRAMC_PADCTL4[0e4]=000022B3
DRAMC_DQIDLY1[210]=0A0F090E
DRAMC_DQIDLY2[214]=050F080C
DRAMC_DQIDLY3[218]=0B050B00
DRAMC_DQIDLY4[21c]=08030B06
DRAMC_R0DELDLY[018]=00001E21
==================================================================
RX DQS perbit delay software calibration
==================================================================
1.0-15 bit dq delay value
==================================================================
bit| 0 1 2 3 4 5 6 7 8 9
--------------------------------------
0 | 14 3 12 6 12 3 13 2 0 9
10 | 2 10 5 10 3 8
--------------------------------------
==================================================================
2.dqs window
x=pass dqs delay value (min~max)center
y=0-7bit DQ of every group
input delay:DQS0 =33 DQS1 = 30
==================================================================
bit DQS0 bit DQS1
0 (1~65)33 8 (4~57)30
1 (1~54)27 9 (1~56)28
2 (1~60)30 10 (1~54)27
3 (1~57)29 11 (1~57)29
4 (2~64)33 12 (1~58)29
5 (1~56)28 13 (1~58)29
6 (1~62)31 14 (2~59)30
7 (1~60)30 15 (1~59)30
==================================================================
3.dq delay value last
==================================================================
bit| 0 1 2 3 4 5 6 7 8 9
--------------------------------------
0 | 14 9 15 10 12 8 15 5 0 11
10 | 5 11 6 11 3 8
==================================================================
==================================================================
TX perbyte calibration
==================================================================
DQS loop = 15, cmp_err_1 = ffff0000
dqs_perbyte_dly.last_dqsdly_pass[0]=15, finish count=1
dqs_perbyte_dly.last_dqsdly_pass[1]=15, finish count=2
DQ loop=15, cmp_err_1 = ffff01aa
DQ loop=14, cmp_err_1 = ffff00aa
dqs_perbyte_dly.last_dqdly_pass[1]=14, finish count=1
DQ loop=13, cmp_err_1 = ffff008a
DQ loop=12, cmp_err_1 = ffff0000
dqs_perbyte_dly.last_dqdly_pass[0]=12, finish count=2
byte:0, (DQS,DQ)=(9,8)
byte:1, (DQS,DQ)=(8,8)
DRAMC_DQODLY1[200]=88888888
DRAMC_DQODLY2[204]=88888888
20,data:89
[EMI] DRAMC calibration passed
===================================================================
MT7621 stage1 code done
CPU=50000000 HZ BUS=16666666 HZ
===================================================================
U-Boot 1.1.3 (Jul 26 2016 - 00:50:05)
Board: Ralink APSoC DRAM: 256 MB
relocate_code Pointer at: 8ff34000
Config XHCI 40M PLL
Allocate 16 byte aligned buffer: 8ff7cd70
Enable NFI Clock
# MTK NAND # : Use HW ECC
NAND ID [C2 F1 80 95 02]
Device not found, ID: c2f1
Not Support this Device!
chip_mode=00000001
Support this Device in MTK table! c2f1
select_chip
[NAND]select ecc bit:4, sparesize :64 spare_per_sector=16
Signature matched and data read!
load_fact_bbt success 1023
load fact bbt success
[mtk_nand] probe successfully!
mtd->writesize=2048 mtd->oobsize=64, mtd->erasesize=131072 devinfo.iowidth=8
..============================================
Ralink UBoot Version: 4.3.0.0
--------------------------------------------
ASIC MT7621A DualCore (MAC to MT7530 Mode)
DRAM_CONF_FROM: Auto-Detection
DRAM_TYPE: DDR3
DRAM bus: 16 bit
Xtal Mode=3 OCP Ratio=1/3
Flash component: NAND Flash
Date:Jul 26 2016 Time:00:50:05
============================================
icache: sets:256, ways:4, linesz:32 ,total:32768
dcache: sets:256, ways:4, linesz:32 ,total:32768
##### The CPU freq = 880 MHZ ####
estimate memory size =256 Mbytes
reset PHY
#Reset_MT7530
SC_DEBUG: Nand Partition Table Magic Found at 120000.
..
Please choose the operation:
1: Load system code to SDRAM via TFTP.
2: Load system code then write to Flash via TFTP.
3: Boot system code via Flash (default).
4: Entr boot command line interface.
9: Load Boot Loader code then write to Flash via TFTP.
You choosed 4
0
4: System Enter Boot Command Line Interface.
U-Boot 1.1.3 (Jul 26 2016 - 00:50:05)
#MT7621 # printenv
bootcmd=tftp
bootdelay=1
baudrate=57600
ipaddr=10.10.10.123
serverip=10.10.10.3
stdin=serial
stdout=serial
stderr=serial
Environment size: 121/4092 bytes
MT7621 # help
? - alias for 'help'
bootm - boot application image from memory
go - start application at address 'addr'
help - print online help
i2ccmd - read/write data to eeprom via I2C Interface
md - memory display
mdio - Ralink PHY register R/W command !!
mm - memory modify (auto-incrementing)
nand - nand command
nm - memory modify (constant address)
printenv- print environment variables
reset - Perform RESET of the CPU
saveenv - save environment variables to persistent storage
sc_cpureg - Sercomm R/W cpu register
sc_dl - Sercomm upgrade command
sc_endian - Sercomm endian test command
sc_eth_test -SC: sc eth test
sc_fl_map - dump sercomm flash map
sc_gpio - Sercomm gpio command
sc_led - Sercomm led command
sc_lp - sercomm loopback test
sc_nand - Sercomm nand command
sc_nmrp - Sercomm nmrp
sc_phy - Sercomm R/W PHY register
sc_ramtest - do sercomm ram tes
sc_tftp_rec - Sercomm nmrp
sc_timer - Sercomm timer command
setenv - set environment variables
tftpboot- boot image via network using TFTP protocol
version - print monitor version
MT7621 #
At this point the only light is an orange power light. The light doesn't change if I let it boot. It also doesn't light when I plug my ethernet cable into any port on the router.
Thanks!