docs/esp32/tutorial: Add example for pin access via registers.

Synchronous access to pins directly via registers.

Signed-off-by: Ihor Nehrutsa <Ihor.Nehrutsa@gmail.com>
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IhorNehrutsa 2023-09-01 18:50:17 +03:00 committed by Damien George
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@ -42,3 +42,83 @@ for this:
The MCPWM0 peripheral is in bit position 17 of the above two registers, hence
the value of ``DPORT_PWM0_CLK_EN``.
Synchronous access to pins directly via registers
-------------------------------------------------
The following code shows how to access pins directly via registers. It has been
tested on a generic ESP32 board. It configures pins 16, 17, 32 and 33 in output
mode via registers, and switches pin output values via registers. Pins 16 and
17 are switched simultaneously.
.. code-block:: python3
from micropython import const
from machine import mem32, Pin
GPIO_OUT_REG = const(0x3FF44004) # GPIO 0-31 output register
GPIO_OUT1_REG = const(0x3FF44010) # GPIO 32-39 output register
GPIO_ENABLE_REG = const(0x3FF44020) # GPIO 0-31 output enable register
GPIO_ENABLE1_REG = const(0x3FF4402C) # GPIO 32-39 output enable register
M16 = 1 << 16 # Pin(16) bit mask
M17 = 1 << 17 # Pin(17) bit mask
M32 = 1 << (32-32) # Pin(32) bit mask
M33 = 1 << (33-32) # Pin(33) bit mask
# Enable pin output mode like
# p16 = Pin(16, mode=Pin.OUT)
# p17 = Pin(17, mode=Pin.OUT)
# p32 = Pin(32, mode=Pin.OUT)
# p33 = Pin(33, mode=Pin.OUT)
mem32[GPIO_ENABLE_REG] = mem32[GPIO_ENABLE_REG] | M16 | M17
mem32[GPIO_ENABLE1_REG] = mem32[GPIO_ENABLE1_REG] | M32 | M33
print(hex(mem32[GPIO_OUT_REG]), hex(mem32[GPIO_OUT1_REG]))
# Set outputs to 1 like
# p16(1)
# p17(1)
# p32(1)
# p33(1)
mem32[GPIO_OUT_REG] = mem32[GPIO_OUT_REG] | M16 | M17
mem32[GPIO_OUT1_REG] = mem32[GPIO_OUT1_REG] | M32 | M33
print(hex(mem32[GPIO_OUT_REG]), hex(mem32[GPIO_OUT1_REG]))
# Set outputs to 0 like
# p16(0)
# p17(0)
# p32(0)
# p33(0)
mem32[GPIO_OUT_REG] = mem32[GPIO_OUT_REG] & ~(M16 | M17)
mem32[GPIO_OUT1_REG] = mem32[GPIO_OUT1_REG] & ~(M32 | M33)
print(hex(mem32[GPIO_OUT_REG]), hex(mem32[GPIO_OUT1_REG]))
while True:
# Set outputs to 1
mem32[GPIO_OUT_REG] = mem32[GPIO_OUT_REG] | M16 | M17
mem32[GPIO_OUT1_REG] = mem32[GPIO_OUT1_REG] | M32 | M33
# Set outputs to 0
mem32[GPIO_OUT_REG] = mem32[GPIO_OUT_REG] & ~(M16 | M17)
mem32[GPIO_OUT1_REG] = mem32[GPIO_OUT1_REG] & ~(M32 | M33)
Output is::
0x0 0x0
0x30000 0x3
0x0 0x0
Pins 16 and 17 are switched synchronously:
.. image:: img/mem32_gpio_output.jpg
Same image on pins 32 and 33.
Note that pins 34-36 and 39 are inputs only. Also pins 1 and 3 are Tx, Rx of the REPL UART,
pins 6-11 are connected to the built-in SPI flash.