MicrOBU/microbu-esp32c5/firmware/main/otm_tx_custom.c

// Sourced from OpenTrafficMap's its-g5-receiver-firmware_txenabled, main/tx_custom.c
// (https://codeberg.org/opentrafficmap/its-g5-receiver-firmware_txenabled, pinned commit
// 674e34128279235ba34c9f8d778f43cf1d075397, no stated license). Reproduced here as generated by
// implementation/external/vanetza-idf/ports/esp_idf/radio_c5.cmake (which hashes the upstream file
// so this copy cannot silently drift) and checked in for readability. The struct layouts
// (x_eb_txdesc_t, x_middle_data_t, x_ebuf_t) and the bit-level manipulation of esp_wifi's private
// tx descriptor are OTM's own reverse engineering of the closed esp_wifi/libphy internals -- not
// documented or supported by Espressif, and not verified independently by this project. The one
// deliberate change from upstream is `result = ieee80211_post_hmac_tx(eb);` below: upstream
// discards that return value, but ESP_OK from this function means the driver accepted the frame
// for submission, not that it was independently observed on air (see
// experiments/evidence/c5-radio-characterization/phy-internals-investigation.md).
#include "esp_private/wifi_os_adapter.h"
#include "esp_wifi.h"
#include "otm_tx_custom.h"
#include <assert.h>
#include <stddef.h>

esp_err_t ieee80211_raw_frame_sanity_check(wifi_interface_t ifx, const void *buffer, int32_t len, bool en_sys_seq);
esp_err_t ieee80211_post_hmac_tx(void *ebuf);
void *ic_ebuf_alloc(const void *packet, uint32_t unknown, uint32_t len);
void *ic_get_default_sched(void);

extern wifi_osi_funcs_t *g_osi_funcs_p;
extern void *g_wifi_global_lock;

typedef struct x_eb_txdesc
{
    uint32_t flags;
    uint32_t field_4;
    uint32_t field_8;
    uint8_t rate;
    uint8_t field_d;
    uint8_t field_e;
    uint8_t field_f;
    uint32_t field_10;
    uint32_t field_14;
    uint32_t timestamp;
    void* sched;
    uint32_t field_20;
    uint32_t field_24;
    uint32_t field_28;
    union {
        uint32_t field_2c_32;
        struct {
            uint8_t field_2c;
            uint8_t field_2d;
            uint8_t field_2e;
            uint8_t field_2f;
        };
    };
    union {
        uint32_t field_30_32;
        struct {
            uint8_t field_30;
            uint8_t field_31;
            uint8_t field_32;
            uint8_t field_33;
        };
    };
    uint32_t field_34;
    uint32_t field_38;
    uint32_t field_3c;
    uint32_t field_40;
    uint32_t field_44;
} x_eb_txdesc_t;
_Static_assert(sizeof(x_eb_txdesc_t) == 0x48, "eb_txdesc size");

typedef struct x_middle_data
{
    uint32_t field_40;
    uint8_t* buf;
    uint32_t field_48;
    uint32_t field_4c;
} x_middle_data_t;
_Static_assert(sizeof(x_middle_data_t) == 0x10, "middle_data size");

typedef struct x_ebuf
{
    uint32_t field_0;
    x_middle_data_t* ds_head;
    x_middle_data_t* ds_tail;
    uint16_t field_c;
    uint16_t field_e;
    uint32_t extra_data_start;
    uint16_t header_length;
    uint32_t data_length;
    uint16_t field_1c;
    uint8_t alloc_type;
    uint8_t field_1f;
    uint32_t field_20;
    uint8_t field_24;
    uint8_t field_25;
    uint8_t field_26;
    uint8_t field_27;
    uint32_t field_28;
    uint8_t field_2c;
    uint32_t field_30;
    uint32_t next_free;
    x_eb_txdesc_t* txdesc;
    uint16_t field_3c;
    uint8_t field_3e;
    uint8_t field_3f;
} x_ebuf_t;
_Static_assert(sizeof(x_ebuf_t) == 0x40, "ebuf size");
_Static_assert(offsetof(x_ebuf_t, txdesc) == 0x38, "ebuf txdesc offset");
_Static_assert(offsetof(x_eb_txdesc_t, rate) == 0x0c, "txdesc rate offset");

esp_err_t esp_wifi_80211_tx_custom(wifi_interface_t ifx, const void *buffer, int32_t len, bool en_sys_seq, wifi_tx_rate_config_t *tx_rate_config, wifi_band_t band, wifi_bandwidth_t bw)
{
    esp_err_t result = 0;

    if (!result)
    {
        g_osi_funcs_p->_mutex_lock(g_wifi_global_lock);
        x_ebuf_t* eb = ic_ebuf_alloc(buffer, 1, len);

        if (eb)
        {
            eb->data_length = 0;
            x_eb_txdesc_t *txdesc_1 = eb->txdesc;
            eb->header_length = len;
            txdesc_1->flags |= 0x4000;
            txdesc_1->sched = ic_get_default_sched();
            wifi_phy_rate_t rate = tx_rate_config->rate;
            x_eb_txdesc_t *txdesc = eb->txdesc;

            if (rate)
                txdesc->rate = (char)rate;
            else if (band != WIFI_BAND_5G)
                txdesc->rate = 0;
            else
                txdesc->rate = (char)WIFI_PHY_RATE_6M;

            wifi_phy_mode_t phymode = tx_rate_config->phymode;

            if (phymode == WIFI_PHY_MODE_HE20)
            {
                txdesc->flags |= 0x80000000;
                txdesc->field_2f =
                    (char)((((uint32_t)tx_rate_config->ersu + 6) & 0xf) << 3)
                    | (txdesc->field_2f & 0x87);

                if ((uint32_t)tx_rate_config->dcm)
                    txdesc->field_31 |= 0x80;
            }
            else if (phymode == WIFI_PHY_MODE_VHT20)
                txdesc->flags |= 0x1000000;

            // OTM's own comment on this line upstream: "No idea if this is correct, but this is
            // what the original code does...". This project always passes WIFI_BW20 (see
            // c5_radio.cpp), so bw_is_bw40 is always 0 here; see the investigation doc above for
            // what is and isn't verified about ITS-G5's 10 MHz channel width on this path.
            uint32_t bw_is_bw40 = bw == WIFI_BW40;
            txdesc->field_8 = (bw_is_bw40 << 0xf) | (txdesc->field_8 & 0xffff7fff);

            if (en_sys_seq)
                txdesc->flags |= 1;

            txdesc->field_10 =
                (txdesc->field_10 & 0xfff3ffff) | ((ifx & WIFI_IF_MAX) << 0x12);
            txdesc->field_14 = 0x100;

            result = ieee80211_post_hmac_tx(eb);
            g_osi_funcs_p->_mutex_unlock(g_wifi_global_lock);
        }
        else
        {
            result = ESP_ERR_NO_MEM;
            g_osi_funcs_p->_mutex_unlock(g_wifi_global_lock);
        }
    }

    return result;
}