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Programming ULP FSM coprocessor using C macros (legacy)

In addition to the existing binutils port for the {IDF_TARGET_NAME} ULP coprocessor, it is possible to generate programs for the ULP FSM coprocessor by embedding assembly-like macros into an {IDF_TARGET_NAME} application. Here is an example how this can be done:

const ulp_insn_t program[] = {
    I_MOVI(R3, 16),         // R3 <- 16
    I_LD(R0, R3, 0),        // R0 <- RTC_SLOW_MEM[R3 + 0]
    I_LD(R1, R3, 1),        // R1 <- RTC_SLOW_MEM[R3 + 1]
    I_ADDR(R2, R0, R1),     // R2 <- R0 + R1
    I_ST(R2, R3, 2),        // R2 -> RTC_SLOW_MEM[R2 + 2]
    I_HALT()
};
size_t load_addr = 0;
size_t size = sizeof(program)/sizeof(ulp_insn_t);
ulp_process_macros_and_load(load_addr, program, &size);
ulp_run(load_addr);

The program array is an array of ulp_insn_t, i.e. ULP coprocessor instructions. Each I_XXX preprocessor define translates into a single 32-bit instruction. Arguments of these preprocessor defines can be register numbers (R0 — R3) and literal constants. See the API reference section at the end of this guide for descriptions of instructions and arguments they take.

Note

Because some of the instruction macros expand to inline function calls, defining such array in global scope will cause the compiler to produce an "initializer element is not constant" error. To fix this error, move the definition of instructions array into local scope.

Note

Load, store and move instructions use addresses expressed in 32-bit words. Address 0 corresponds to the first word of RTC_SLOW_MEM. This is different to how address arguments are handled in assembly code of the same instructions. See the section ulp-fsm-addressing for more details for reference.

To generate branch instructions, special M_ preprocessor defines are used. M_LABEL define can be used to define a branch target. Label identifier is a 16-bit integer. M_Bxxx defines can be used to generate branch instructions with target set to a particular label.

Implementation note: these M_ preprocessor defines will be translated into two ulp_insn_t values: one is a token value which contains label number, and the other is the actual instruction. ulp_process_macros_and_load function resolves the label number to the address, modifies the branch instruction to use the correct address, and removes the extra ulp_insn_t token which contains the label numer.

Here is an example of using labels and branches:

const ulp_insn_t program[] = {
    I_MOVI(R0, 34),         // R0 <- 34
    M_LABEL(1),             // label_1
    I_MOVI(R1, 32),         // R1 <- 32
    I_LD(R1, R1, 0),        // R1 <- RTC_SLOW_MEM[R1]
    I_MOVI(R2, 33),         // R2 <- 33
    I_LD(R2, R2, 0),        // R2 <- RTC_SLOW_MEM[R2]
    I_SUBR(R3, R1, R2),     // R3 <- R1 - R2
    I_ST(R3, R0, 0),        // R3 -> RTC_SLOW_MEM[R0 + 0]
    I_ADDI(R0, R0, 1),      // R0++
    M_BL(1, 64),            // if (R0 < 64) goto label_1
    I_HALT(),
};
RTC_SLOW_MEM[32] = 42;
RTC_SLOW_MEM[33] = 18;
size_t load_addr = 0;
size_t size = sizeof(program)/sizeof(ulp_insn_t);
ulp_process_macros_and_load(load_addr, program, &size);
ulp_run(load_addr);

API Reference

inc/ulp.inc