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romconsole.rst

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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 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