8ee3decdba
The previously used splits between memory allocated for ROM code,
2nd stage bootloader and the app were somewhat safe and conservative.
This resulted in some space being unavailable for static allocation
in the app.
This commit increases the space available for static allocation to the
maximum possible amount.
1. Some of the ROM code static allocation is only used in UART/USB/SPI
download modes. This region ("shared buffers") has been placed at
the lower end of ROM memory area, to be reusable in flash boot
mode. The 2nd stage bootloader linker script is modified to "pack"
all sections exactly up to the end but with roughly 8K margin between
startup stacks.
2. Instead of calculating the sections placement and hardcoding the
addresses in the LD script again, rewrite it to calculate the
start address of each memory region automatically based on the
logic above.
3. Adjust the app memory layout (SRAM_IRAM_END) accordingly,
increasing the space available for static allocation.
Overall these changes increase the space available for static
allocation by about 78kB.
The downside of these changes is that the 2nd stage bootloader .data
segment is now directly adjacent to the startup stack on the PRO CPU.
Previously, there was effectively about 78kB of extra stack space for
the PRO CPU, before the stack would run into the data segment.
System Notes
Timekeeping
The following are the timekeeping mechanisms available and their differences:
- System time (
esp_system_get_time)
Time with the origin at g_startup_time. The implementation is not handled by esp_system,
but it does provide a default implementation using RTC timer. Currently, esp_timer
provides system time, since the hardware timers are under the control of that
component. However, no matter the underlying timer, the system time provider
should maintain the definition of having the origin point at g_startup_time.
esp_timertime (esp_timer_get_time)
This is the time read from an underlying hardware timer, controlled through config. Origin is at the point where the underlying timer starts counting.
newlibtime (gettimeofday)
Timekeeping function in standard library. Can be set (settimeofday) or moved forward/backward (adjtime);
with the possibility of the changes being made persistent through config.
Currently implemented in terms of system time, as the point of origin is fixed.
If persistence is enabled, RTC time is also used in conjuction with system time.
- RTC time (
esp_rtc_get_time_us)
Time read from RTC timer.