cdc_rx.c

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#include "icarus/cdc_rx.h"
#include "icarus/config.h"
#include <stddef.h>
 
/* ---- Backing storage in DTCM_PRIV --------------------------------------- */
 
DTCM_DATA_PRIV static volatile uint8_t  rx_buf[CDC_RX_BUF_SIZE];
DTCM_DATA_PRIV static volatile uint32_t rx_head;
DTCM_DATA_PRIV static volatile uint32_t rx_tail;
 
/* ---- Privileged implementations (run in priv mode, ITCM hot path) ------ */
 
ITCM_FUNC void __cdc_rx_init(void) {
    rx_head = 0;
    rx_tail = 0;
}
 
ITCM_FUNC void __cdc_rx_push(const uint8_t *data, uint32_t len) {
    if ((data == NULL) || (len == 0u)) {
        return;
    }
    for (uint32_t i = 0u; i < len; i++) {
        uint32_t next = (rx_head + 1u) % (uint32_t)CDC_RX_BUF_SIZE;
        if (next == rx_tail) {
            break;
        }
        rx_buf[rx_head] = data[i];
        rx_head = next;
    }
}
 
ITCM_FUNC bool __cdc_rx_read_byte(uint8_t *out) {
    if ((out == NULL) || (rx_head == rx_tail)) {
        return false;
    }
    *out = rx_buf[rx_tail];
    rx_tail = (rx_tail + 1u) % (uint32_t)CDC_RX_BUF_SIZE;
    return true;
}
 
ITCM_FUNC uint32_t __cdc_rx_available(void) {
    uint32_t h = rx_head;
    uint32_t t = rx_tail;
    if (h >= t) {
        return h - t;
    }
    return ((uint32_t)CDC_RX_BUF_SIZE - t) + h;
}