readme update, separated document for the PCB v1.7 upgrade

README.md

@@ -12,16 +12,9 @@ board release 3 with SDRAM, Successor of
 [Schematics](/doc/schematics.pdf) is mostly complete.
 PCB routing is mostly complete too. PCB produced when at version 1.7
 and big things work like USB-JTAG, SDRAM, SDCARD, HDMI, FLASH, RTC, I2C
-but there are issues:
+but there are issues, luckily most of them are can be fixed by an
-PCB v1.7 has small issues like SHUTDOWN not connected.
+[Upgrade for PCB v1.7](/doc/doc/pcb-v1.7-upgrade.md)
-When SHUTDOWN is connnected to 3.3V and released, usually board wakes up again,
+AUDIO, OLED and 433.92MHz antenna are currently untested.
-cause of that is probably FT231X generating 2.5V from internal regulator
-and raising up 3.3V line over FPGA protection diodes.
-WiFi won't work if its pins to SDCARD are connected, WiFi disable
-jumper won't work if WiFi enable is held high by FPGA.
-For some monitors I2C works and for some it doesn't.
-Try to increase i2c pullup resistors 470->1.2k.
-AUDIO, OLED are currently untested.
 
 3D preview
 

doc/pcb-v1.7-upgrade.md

@@ -0,0 +1,72 @@
+# PCB v1.7 upgrade
+
+This is the first board produced, most important
+parts work which is mirracle in itself, and there
+are some mistakes, luckily most of them can be fixed.
+
+FIX: Replace this parts:
+
+    D11=LED (High efficiency RED recommended)
+    R4,R25,R26=4.7k
+
+D11 and R4 are are on the back side on the left,
+under the edge of SDRAM chip.
+
+R25 and R26 are on the back side top,
+under the GPDI connector.
+
+Optionally, as alternative software shutdown, 
+connected J2 "25-" pin to R13-D15 junction.
+
+Mount:
+
+    SDCARD:  SCHD3A0100
+    U11 I2C:     PCA9306D SOIC-8 150-mil
+    U10 FLASH:   IS25LP032D-JNLE-TR SOIC-8 150mil
+    U9 WIFI:     ESP32, but not all pins! read below:
+
+Don't connect ESP32 pins leading to SD card
+those are 6 central pins from on the top 10-pin row of
+ESP32 chip (only 2 pins on left side and 2 pins on right
+side shuould be connected). Either cut the traces or carefully
+solder without touching SD card pins.
+
+# What is fixed
+
+Shutdown:
+
+on assembled PCB v1.7, D11=1N4148 and R4=15k will
+keep waking the board up after shutdown signal because FT231x internal
+regulator will provide enough voltage (cca 2.5V will appear at 3.3V line)
+and that is enough to wakeup the board because voltage
+on ENABLE pin at switching regulators will be above its turn on
+threshold of 1.5V.
+
+Using higher voltage drop diode (RED, YELLOW or GREEN LED cca 1.7-2V, not
+BLUE or WHITE) and adequate resistor, the voltage at ENABLE pin is now about
+1.3V, inside of the switching regulator's hysteresis range. ENABLE is
+not above turn-on threshold neither below turn-off threshold so it will
+self-hold switching regulator during normal operation and at controlled
+shutdown signal, it will drop below turn-off threshold, allowing reliable
+shutdown.
+
+Software shutdown is not routed to BGA pads so alternative patch is
+to connect any GPIO (we recommend "25-") to SHUTDOWN.
+
+I2C:
+
+Too low pull up resistors (470 ohm) are at 5V side of the level converter PCA9306
+and some monitors won't tolerate that. Data traffic at i2c will be
+errorneously received by some monitors and some serious problem may arrise
+if monitor interprets some data garbage as random write command, overwriting
+its internal settings, then monitor will become useless.
+
+Correct pull up resistors are 4.7k and they work properly.
+
+WIFI:
+
+On PCB v1.7, SD card is connected to ESP32 pins that are widely advertised
+as SD card pins, but the problem is those pins are shared with internal flash
+chip and ESP32 won't boot from its SPI FLASH if anything is connected there.
+SD card should be connected on some other pins, probably HSPI. It has not
+yet been verified will that work.