diff --git a/configs/stm32f103-minimum/README.txt b/configs/stm32f103-minimum/README.txt index 96e7be7a79..4ddee1fb07 100644 --- a/configs/stm32f103-minimum/README.txt +++ b/configs/stm32f103-minimum/README.txt @@ -428,6 +428,49 @@ Where is one of the following: configuration. This configuration has far fewer features than the nsh configuration but is also a fraction of the size. + This minnsh configuration is a "proof-of-concept" and not very usable in + its current state. This configuration was created by disabling + everything possible INCLUDING file system support. Without file system + support, NuttX is pretty much crippled. Here are some of the + consequences of disabling the file system: + + - All features that depend on the file system are lost: device drivers, + mountpoints, message queues, named semaphores. + + - Without device drivers, you cannot interact with the RTOS using POSIX + interfaces. You would have to work with NuttX as with those other + tiny RTOSs: As a scheduler and a callable hardare abstraction layer + (HAL). + + - You cannot use any of the NuttX upper half device drivers since they + depend on the pseudo-file system and device nodes. You can, of + course, continue to use the lower half drivers either directly. Or, + perhaps, you could write some custom minnsh upper half drivers that + do not depend on a file system and expose a HAL interface. + + There is a special version of readline() the NSH uses when there is no + file system. It uses a special up_putc() to write data to the console + and a special function up_getc() to read data from the console. + + - The current up_getc() implementationsa are a kludge. They are + analogous to the up_putc() implementations: They directly poll the + hardware for serial availability, locking up all lower priority tasks + in the entire system while they poll. So a version of NSH that uses + up_getc() essentially blocks the system until a character is received. + + This, of course, could be fixed by creating a special, upper half + implementation of the interrupt-driven serial lower half (like + stm32_serial) that just supports single character console I/O + (perhaps called up_putc and up_getc?). The NSH could wait for serial + input without blocking the system. But then that would increase the + footprint too. + + So although the minnsh configurations are a good starting point for + making things small, they not are really very practical. Why might + you want a NuttX minnsh solution? Perhaps you have software that runs + on a family of chips including some very tiny MCUs. Then perhaps having + the RTOS compatibility would justify the loss of functionality? + STATUS: 2016-06-03: Using that config I got this: @@ -446,6 +489,50 @@ Where is one of the following: Mem: 18624 2328 16296 16296 nsh> + 2016-06-07: As another experiment, I tried enabling just (1) the file + system, (2) the console device, and (3) the upper half serial driver in + the minnsh configuration. With these changes, NSH should behave better + nd we preserve the device driver interface. I made the following + configuration changes: + + Enable the file system: + CONFIG_NFILE_DESCRIPTORS=5 + CONFIG_NFILE_STREAMS=5 + + Enable the console device: + CONFIG_DEV_CONSOLE=y + + Disable most new NSH commands. Some like 'ls' are really mandatory + with a file system: + CONFIG_NSH_DISABLE_xxx=y + + Enable the upper half serial driver: + CONFIG_SERIAL=y + CONFIG_STANDARD_SERIAL=y + + Enable the USART1 serial driver: + CONFIG_STM32_USART1=y + CONFIG_STM32_USART1_SERIALDRIVER=y + CONFIG_USART1_SERIAL_CONSOLE=y + + CONFIG_USART1_2STOP=0 + CONFIG_USART1_BAUD=115200 + CONFIG_USART1_BITS=8 + CONFIG_USART1_PARITY=0 + CONFIG_USART1_RXBUFSIZE=16 + CONFIG_USART1_TXBUFSIZE=16 + + The resulting code was bigger as expected: + + $ arm-none-eabi-size nuttx + text data bss dec hex filename + 20093 88 876 21057 5241 nuttx + + I am sure that other things that could be disabled were also drawn into + the build, so perhaps this could be reduced. But as a ballpark + estimate, it looks like the cost of basic file system and serial console + driver support is around 7+KB. + nsh: --- Configures the NuttShell (nsh) located at apps/examples/nsh. This