psram_pool.cpp

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// Copyright (C) 2026 Douglas Quigg (dstroy0) <dquigg123@gmail.com>
// SPDX-License-Identifier: AGPL-3.0-or-later
 
/**
 * @file psram_pool.cpp
 * @brief Buffer placement policy + SPI DMA ping-pong index manager (see psram_pool.h).
 */
 
#include "services/psram_pool/psram_pool.h"
 
#if DETWS_ENABLE_PSRAM_POOL
 
namespace
{
// Does `size` fit in DRAM while still leaving `reserve` free? Overflow-safe (64-bit sum).
bool dram_fits(size_t size, size_t free_dram, size_t reserve)
{
    return (uint64_t)size + reserve <= (uint64_t)free_dram;
}
} // namespace
 
DetwsPlace detws_psram_place(size_t size, bool dma_required, size_t free_dram, size_t free_psram,
                             size_t psram_threshold, size_t dram_reserve)
{
    if (size == 0)
        return DetwsPlace::PLACE_FAIL;
 
    bool d_fits = dram_fits(size, free_dram, dram_reserve);
    bool p_fits = size <= free_psram;
 
    if (dma_required) // PSRAM is not DMA-capable: DRAM or bust.
        return d_fits ? DetwsPlace::PLACE_DRAM : DetwsPlace::PLACE_FAIL;
 
    if (size >= psram_threshold) // large / cold: prefer PSRAM.
    {
        if (p_fits)
            return DetwsPlace::PLACE_PSRAM;
        if (d_fits)
            return DetwsPlace::PLACE_DRAM;
        return DetwsPlace::PLACE_FAIL;
    }
 
    // small / hot: prefer DRAM.
    if (d_fits)
        return DetwsPlace::PLACE_DRAM;
    if (p_fits)
        return DetwsPlace::PLACE_PSRAM;
    return DetwsPlace::PLACE_FAIL;
}
 
void detws_pingpong_init(PingPong *pp)
{
    if (pp)
        pp->fill_idx = 0;
}
 
uint8_t detws_pingpong_fill_index(const PingPong *pp)
{
    return pp ? pp->fill_idx : 0;
}
 
uint8_t detws_pingpong_drain_index(const PingPong *pp)
{
    return pp ? (uint8_t)(pp->fill_idx ^ 1u) : 1;
}
 
uint8_t detws_pingpong_swap(PingPong *pp)
{
    if (!pp)
        return 0;
    pp->fill_idx ^= 1u;
    return pp->fill_idx;
}
 
#endif // DETWS_ENABLE_PSRAM_POOL