Datasheet

0x00000016
16 bit pointer
Pointer to a public data lookup table (rom_data_table)
0x00000018
16 bit pointer
Pointer to a helper function (rom_table_lookup())
2.7.3.1. Bootrom Functions
The Bootrom contains a number of public functions that provide useful RP2040 functionality that might be needed in the
absence of any other code on the device, as well as highly optimized versions of certain key functionality that would
otherwise have to take up space in most user binaries.
These functions are normally made available to the user by the Pico SDK, however a lower level method is provided to
locate them (their locations may change with each Bootrom release) and call them directly.
Assuming the three bytes starting at address 0x00000010 are ('M', 'u', 0x01) then the three halfwords starting at offset
0x00000014 are valid.
These three values can be used to dynamically locate other functions or data within the Bootrom. The version byte at
offset 0x00000013 is informational and should not be used to infer the exact location of any functions.
The following code from the Pico SDK shows how the three 16-bit pointers are used to lookup other functions or data.
Pico SDK: https://github.com/raspberrypi/pico-sdk/tree/pre_release/src/rp2_common/pico_bootrom/bootrom.c Lines 10 - 28
10 // Bootrom function: rom_table_lookup
11 // Returns the 32 bit pointer into the ROM if found or NULL otherwise.
12 typedef void *(*rom_table_lookup_fn)(uint16_t *table, uint32_t code);
13
14 // Convert a 16 bit pointer stored at the given rom address into a 32 bit pointer
15 #define rom_hword_as_ptr(rom_address) (void *)(uintptr_t)(*(uint16_t *)rom_address)
16
17 void *rom_func_lookup(uint32_t code) {
18 rom_table_lookup_fn rom_table_lookup = (rom_table_lookup_fn) rom_hword_as_ptr(0x18);
19 uint16_t *func_table = (uint16_t *) rom_hword_as_ptr(0x14);
20 return rom_table_lookup(func_table, code);
21 }
22
23 void *rom_data_lookup(uint32_t code) {
24 rom_table_lookup_fn rom_table_lookup = (rom_table_lookup_fn) rom_hword_as_ptr(0x18);
25 uint16_t *data_table = (uint16_t *) rom_hword_as_ptr(0x16);
26 return rom_table_lookup(data_table, code);
27 }
The code parameter correspond to the CODE values in the tables below, and is calculated as follows:
uint32_t rom_table_code(char c1, char c2) {
Ê return (c2 << 8) | c1;
}
2.7.3.1.1. Fast Bit Counting / Manipulation Functions
These are optimized versions of common bit counting / manipulation functions.
In general you do not need to call these methods directly as the Pico SDK pico_aeabi_bits library replaces the
corresponding standard compiler library functions by default so that the standard functions such as __builtin_popcount or
__clzdi2 uses the corresponding Bootrom implementations automatically (see pico_bit_ops for more details).
These functions have changed in speed slightly between version 1 (V1) of the bootrom and version 2 (v2) .Fast Bit
RP2040 Datasheet
2.7. Bootrom 117