Inspired by `digitalReadFast` and `digitalWriteFast` and how they can compile to just one instruction, I wanted to see if it was possible to access and change the bit-band memory regions using code that also compiles to just a few instructions, and without using #defines. Hooray for modern C++ features!
Example use:
I've attached the current version of the code and a `main` file so you can see how it compiles. Compile with the `-S` option to see the assembly. I use PlatformIO. Unfortunately, this forum claims `.ini` files are "invalid", so here's the `platformio.ini` contents:
If you run into trouble or find that the code doesn't actually compile into just a few instructions, it's possible your build system is different than what I'm using. When I resurrected this today, I experimented with minimizing the source and it still worked for me. When I started playing with this last year, I found that there were some other changes I had to make to get it to work. These included using only `uint32_t` bit masks and using a `switch` statement instead of the array access in `countTrailingZeros`. I also found that I had to have two `countTrailingZeros` versions, one for 8-bit and one for 32-bit. Even then, I was having some difficulty. But in any case, it works today using the latest PlatformIO Teensy tools (1.148.0).
The sources:
View attachment bitband_routines.h
View attachment bitband_main.cpp
Example use:
Code:
// 8-bit
setGPIOBit(&UART0_C2, UART_C2_TE);
clearGPIOBit(&UART0_C2, UART_C2_TE);
if (readGPIOBit(&UART0_C2, UART_C2_TE)) {
// Stuff
}
// 32-bit
setGPIOBit(&LPUART0_CTRL, LPUART_CTRL_TE);
clearGPIOBit(&LPUART0_CTRL, LPUART_CTRL_TE);
if (readGPIOBit(&LPUART0_CTRL, LPUART_CTRL_TE)) {
// Stuff
}I've attached the current version of the code and a `main` file so you can see how it compiles. Compile with the `-S` option to see the assembly. I use PlatformIO. Unfortunately, this forum claims `.ini` files are "invalid", so here's the `platformio.ini` contents:
Code:
[common]
build_flags = -Wall -S
monitor_speed = 115200
[env:teensy36]
platform = teensy
board = teensy36
framework = arduino
build_flags = ${common.build_flags}
monitor_speed = ${common.monitor_speed}If you run into trouble or find that the code doesn't actually compile into just a few instructions, it's possible your build system is different than what I'm using. When I resurrected this today, I experimented with minimizing the source and it still worked for me. When I started playing with this last year, I found that there were some other changes I had to make to get it to work. These included using only `uint32_t` bit masks and using a `switch` statement instead of the array access in `countTrailingZeros`. I also found that I had to have two `countTrailingZeros` versions, one for 8-bit and one for 32-bit. Even then, I was having some difficulty. But in any case, it works today using the latest PlatformIO Teensy tools (1.148.0).
The sources:
View attachment bitband_routines.h
View attachment bitband_main.cpp
