Merge branch 'docs/romconsole_docs' into 'master'

Some documentation for the undocumented ROM console.

See merge request !936

docs/api-guides/index.rst

@@ -15,3 +15,4 @@ API Guides
    ULP Coprocessor <ulp>
    Unit Testing <unit-tests>
    Application Level Tracing <app_trace>
+   ROM debug console <romconsole>

docs/api-guides/romconsole.rst

@@ -0,0 +1,113 @@
+ESP32 ROM console
+=================
+
+When an ESP32 is unable to boot from flash ROM (and the fuse disabling it hasn't been blown), it boots into a rom console. The console
+is based on TinyBasic, and statements entered should be in the form of BASIC statements. As is common in the BASIC language, without a 
+preceeding line number, commands entered are executed immediately; lines with a prefixed line number are stored as part of a program.
+
+Full list of supported statements and functions
+===============================================
+
+System
+------
+
+- BYE		- *exits Basic, reboots ESP32, retries booting from flash*
+- END 		- *stops execution from the program, also "STOP"*
+- MEM		- *displays memory usage statistics*
+- NEW		- *clears the current program*
+- RUN		- *executes the current program*
+
+IO, Documentation
+-----------------
+
+- PEEK( address )	- *get a 32-bit value from a memory address*
+- POKE			- *write a 32-bit value to memory*
+- USR(addr, arg1, ..) - *Execute a machine language function*
+- PRINT expression	- *print out the expression, also "?"*
+- PHEX expression	- *print expression as a hex number*
+- REM stuff		- *remark/comment, also "'"*
+
+Expressions, Math
+-----------------
+
+- A=V, LET A=V	- *assign value to a variable*
+- +, -, \*, / - *Math*
+- <,<=,=,<>,!=,>=,> - *Comparisons*
+- ABS( expression )  - *returns the absolute value of the expression*
+- RSEED( v ) - *sets the random seed to v*
+- RND( m ) - *returns a random number from 0 to m*
+- A=1234 - * Assign a decimal value*
+- A=&h1A2 - * Assign a hex value*
+- A=&b1001 - *Assign a binary value*
+
+Control
+-------
+
+- IF expression THEN statement - *perform statement if expression is true*
+- FOR variable = start TO end	- *start for block*
+- FOR variable = start TO end STEP value - *start for block with step*
+- NEXT - *end of for block*
+- GOTO linenumber - *continue execution at this line number*
+- GOSUB linenumber - *call a subroutine at this line number*
+- RETURN	- *return from a subroutine*
+- DELAY		- *Delay a given number of milliseconds*
+
+Pin IO
+------
+- IODIR		- *Set a GPIO-pin as an output (1) or input (0)*
+- IOSET		- *Set a GPIO-pin, configured as output, to high (1) or low (0)*
+- IOGET		- *Get the value of a GPIO-pin*
+
+
+Example programs
+================
+
+Here are a few example commands and programs to get you started...
+
+Read UART_DATE register of uart0
+--------------------------------
+
+::
+
+	> PHEX PEEK(&h3FF40078)
+	15122500
+
+Set GPIO2 using memory writes to GPIO_OUT_REG
+---------------------------------------------
+
+Note: you can do this easier with the IOSET command
+
+::
+
+	> POKE &h3FF44004,PEEK(&h3FF44004) OR &b100
+
+Get value of GPIO0
+------------------
+
+::
+
+	> IODIR 0,0
+	> PRINT IOGET(0)
+	0
+
+Blink LED
+---------
+
+Hook up an LED between GPIO2 and ground. When running the program, the LED should blink 10 times.
+
+::
+
+	10 IODIR 2,1
+	20 FOR A=1 TO 10
+	30 IOSET 2,1
+	40 DELAY 250
+	50 IOSET 2,0
+	60 DELAY 250
+	70 NEXT A
+	RUN
+
+Credits
+=======
+
+The ROM console is based on "TinyBasicPlus" by Mike Field and Scott Lawrence, which is based on "68000 TinyBasic" by Gordon Brandly
+