[microTVM] Refactor required external functions in CRT to platform-template.c

[mehrdadh]

This PR refactors all the necessary functions for a CRT project into platform-template.c file. Using this PR the content of CRT template project is as follow:

.
├── crt_config
│   ├── crt_config-template.h
├── Makefile.template
├── microtvm_api_server.py
└── src
    ├── main.cc
    └── platform-template.c

The content of platform-template.c is as follows. This file shows the minimum implementation that is required for using a microTVM generated MLF file in a different environment.

#include <dlpack/dlpack.h>
#include <stdarg.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <tvm/runtime/crt/error_codes.h>
#include <tvm/runtime/crt/page_allocator.h>

uint8_t memory[MEMORY_SIZE_BYTES];
MemoryManagerInterface* memory_manager;

// Called when an internal error occurs and execution cannot continue.
void TVMPlatformAbort(tvm_crt_error_t error_code) { exit(1); }

// Called by the microTVM RPC server to implement TVMLogf.
size_t TVMPlatformFormatMessage(char* out_buf, size_t out_buf_size_bytes,
                                                      const char* fmt, va_list args) {
  return vsprintf(out_buf, fmt, args);
}

// Allocate memory for use by TVM.
tvm_crt_error_t TVMPlatformMemoryAllocate(size_t num_bytes, DLDevice dev,
                                                                void** out_ptr) {
  return memory_manager->Allocate(memory_manager, num_bytes, dev, out_ptr);
}

// Free memory used by TVM.
tvm_crt_error_t TVMPlatformMemoryFree(void* ptr, DLDevice dev) {
  return memory_manager->Free(memory_manager, ptr, dev);
}

// Start a device timer.
tvm_crt_error_t TVMPlatformTimerStart() { return kTvmErrorNoError; }

// Stop the running device timer and get the elapsed time (in microseconds).
tvm_crt_error_t TVMPlatformTimerStop(double* elapsed_time_seconds) {
  return kTvmErrorNoError;
}

// Platform-specific before measurement call.
tvm_crt_error_t TVMPlatformBeforeMeasurement() { return kTvmErrorNoError; }

// Platform-specific after measurement call.
tvm_crt_error_t TVMPlatformAfterMeasurement() { return kTvmErrorNoError; }

// Fill a buffer with random data.
tvm_crt_error_t TVMPlatformGenerateRandom(uint8_t* buffer, size_t num_bytes) {
  return kTvmErrorNoError;
}

// Initialize TVM inference.
tvm_crt_error_t TVMPlatformInitialize() {
  int status =
      PageMemoryManagerCreate(&memory_manager, memory, sizeof(memory), 8 /* page_size_log2 */);
  if (status != 0) {
    fprintf(stderr, "error initiailizing memory manager\n");
    return kTvmErrorPlatformMemoryManagerInitialized;
  }
  return kTvmErrorNoError;
}

Using the same idea, various project types for Zephyr and Arduino was refactored.

In addition, these templates files are also added along with crt_config-template.h (which was accidentally removed in #13812) to generated model library format (MLF). Here is the updated structure of a MLF file:

.
├── codegen
│   └── host
├── metadata.json
├── parameters
│   └── default.params
├── runtime
│   ├── include
│   ├── Makefile
│   └── src
├── src
│   └── default.relay
└── templates
    ├── crt_config-template.h
    ├── platform-template.c

[tvm-bot]

Thanks for contributing to TVM! Please refer to the contributing guidelines https://tvm.apache.org/docs/contribute/ for useful information and tips. Please request code reviews from Reviewers by @-ing them in a comment.

• cc @alanmacd, @gromero, @leandron, @mkatanbaf _{See #10317 for details}

_{Generated by tvm-bot}

[mehrdadh]

@alanmacd thanks for the review! I addressed them but haven't pushed since I'm waiting to see the result of ci_cortexm tests in case anything is broken

[mkatanbaf]

Thanks @mehrdadh, I left a few comments.

[mkatanbaf]

do we need to place the prototypes of the functions defined in platform.c here?

[mehrdadh]

wdym?

[mkatanbaf]

Move this function to platform.c?

[mehrdadh]

done

[mkatanbaf]

LGTM, just left a few minor comments.

[areusch]

thanks @mehrdadh ! the main question i have here is around making TVMPlatform functions weak--i don't think we should do that, unless i'm missing something. would love to hear others' opinions

[areusch]

how come these are weak? if you miss implementing one, could you accidentally link the default and then wind up with two implementations?

[mehrdadh]

The idea here is that platform.c has one implementation of these functions which is added by default to the project. But in case the user wants to change the implementation, they could reimplement it in their main.c
That's why it is defined as weak.

[guberti]

I'm a fan of these being weak - I think allowing the user to change the implementation is worth the increased complexity.

[mehrdadh]

After discussing this with @alanmacd and @areusch, we decided to remove weak option since it is not widely supported in various compilers.

[areusch]

use consistent caps (UART vs Uart; i prefer Uart because the string parses easier)

[mehrdadh]

done

[areusch]

initialize the Uart after you are ready to receive stuff

[mehrdadh]

UartInit initialize both transmit and receive

[mkatanbaf]

I guess what @areusch means here (and correct me if I'm wrong) is to init Uart once the platform (including memory, rpc for example) is initialized. Otherwise, the received data might drop or even cause errors (by trying to write into memory spaces that are not allocated yet)

[mehrdadh]

That makes sense. I changed the order.

[guberti]

Left a few nits, but looks good to me!

[guberti]

I'm a fan of these being weak - I think allowing the user to change the implementation is worth the increased complexity.

[guberti]

Defining these constants is a really nice improvement!