Freestanding on Kovacsics Robert

Bootstrapping Freestanding, part 2

Sun, 04 Oct 2026 14:03:43 +0100

Parts: 1, 2

Time to start using the C library! Though this article is about all the things that can go wrong when you start to do that. First, let’s replace the infinite loop at the end of init.S with a jump to the C library’s entry point (in this case newlib).

init.S

@@ -21,19 +28,38 @@ _entry:
 stmia r9!, {r0-r7}
 b 1b
 2:

-1: b 1b
+ b _mainCRTStartup

The first issue is:

Bootstrapping Freestanding, part 1

Sun, 13 Sep 2026 23:06:37 +0100

Parts: 1, 2

Recently I was building the platform support for a Cortex-R5 microcontroller. It is executing out of QSPI flash, with SRAM (static RAM, doesn’t need a controller set up unlike DRAM) and tightly coupled memory: ATCM is typically for instructions, and BTCM is typically for data. The benefit of {A,B}TCM is much faster access, and it is present even when doing erases/writes to the flash. On the other hand, it is not accessible for other devices in the system (e.g. network DMA engines), unlike the SRAM.