BlueSCSI-v2/lib/ZuluSCSI_platform_RP2040/scsi_accel_rp2040.cpp

/* Data flow in SCSI acceleration:
 *
 * 1. Application provides a buffer of bytes to send.
 * 2. Code in this module adds parity bit to the bytes and packs two bytes into 32 bit words.
 * 3. DMA controller copies the words to PIO peripheral FIFO.
 * 4. PIO peripheral handles low-level SCSI handshake and writes bytes and parity to GPIO.
 */

#include "ZuluSCSI_platform.h"
#include "ZuluSCSI_log.h"
#include "scsi_accel_rp2040.h"
#include "scsi_accel.pio.h"
#include <hardware/pio.h>
#include <hardware/dma.h>
#include <hardware/irq.h>
#include <hardware/structs/iobank0.h>

#define SCSI_DMA_PIO pio0
#define SCSI_DMA_SM 0
#define SCSI_DMA_CH 0
#define SCSI_DMA_SYNC_SM 1
#define SCSI_DMA_SYNC_CH 1

enum scsidma_buf_sel_t { SCSIBUF_NONE = 0, SCSIBUF_A = 1, SCSIBUF_B = 2 };

#define DMA_BUF_SIZE 128
static struct {
    uint8_t *app_buf; // Buffer provided by application
    uint32_t app_bytes; // Bytes available in application buffer
    uint32_t dma_bytes; // Bytes that have been converted to DMA buffer so far
    
    uint8_t *next_app_buf; // Next buffer from application after current one finishes
    uint32_t next_app_bytes; // Bytes in next buffer

    // Synchronous mode?
    int syncOffset;
    int syncPeriod;
    int syncOffsetDivider; // Autopush/autopull threshold for the write pacer state machine
    int syncOffsetPreload; // Number of items to preload in the RX fifo of scsi_sync_write

    // PIO configurations
    uint32_t pio_offset_async_write;
    uint32_t pio_offset_async_read;
    uint32_t pio_offset_sync_write_pacer;
    uint32_t pio_offset_sync_write;
    pio_sm_config pio_cfg_async_write;
    pio_sm_config pio_cfg_async_read;
    pio_sm_config pio_cfg_sync_write_pacer;
    pio_sm_config pio_cfg_sync_write;

    // DMA configurations
    dma_channel_config dma_write_config; // Data from RAM to first state machine
    dma_channel_config dma_write_pacer_config; // In synchronous mode only, transfer between state machines

    // We use two DMA buffers alternatively
    // The buffer contains the data bytes with parity added.
    scsidma_buf_sel_t dma_current_buf;
    uint32_t dma_countA;
    uint32_t dma_countB;
    uint32_t dma_bufA[DMA_BUF_SIZE];
    uint32_t dma_bufB[DMA_BUF_SIZE];
} g_scsi_dma;

enum scsidma_state_t { SCSIDMA_IDLE = 0,
                       SCSIDMA_WRITE, SCSIDMA_WRITE_DONE,
                       SCSIDMA_READ };
static volatile scsidma_state_t g_scsi_dma_state;
static bool g_channels_claimed = false;

// Fill DMA buffer and return number of words ready to be transferred
static uint32_t refill_dmabuf(uint32_t *buf)
{
    if (g_scsi_dma.app_bytes == 0 && g_scsi_dma.next_app_bytes > 0)
    {
        g_scsi_dma.dma_bytes = 0;
        g_scsi_dma.app_buf = g_scsi_dma.next_app_buf;
        g_scsi_dma.app_bytes = g_scsi_dma.next_app_bytes;
        g_scsi_dma.next_app_buf = 0;
        g_scsi_dma.next_app_bytes = 0;
    }

    uint32_t count = (g_scsi_dma.app_bytes - g_scsi_dma.dma_bytes) / 2;
    if (count > DMA_BUF_SIZE) count = DMA_BUF_SIZE;

    uint16_t *src = (uint16_t*)&g_scsi_dma.app_buf[g_scsi_dma.dma_bytes];
    uint16_t *end = src + count;
    uint32_t *dst = buf;
    while (src < end)
    {
        uint16_t input = *src++;
        *dst++ = (g_scsi_parity_lookup[input & 0xFF])
               | ((g_scsi_parity_lookup[input >> 8]) << 16);
    }

    g_scsi_dma.dma_bytes += count * 2;

    // Check if this buffer has been fully processed
    if (g_scsi_dma.dma_bytes >= g_scsi_dma.app_bytes)
    {
        assert(g_scsi_dma.dma_bytes == g_scsi_dma.app_bytes);
        g_scsi_dma.dma_bytes = 0;
        g_scsi_dma.app_buf = g_scsi_dma.next_app_buf;
        g_scsi_dma.app_bytes = g_scsi_dma.next_app_bytes;
        g_scsi_dma.next_app_buf = 0;
        g_scsi_dma.next_app_bytes = 0;
    }

    return count;
}

// Select GPIO from PIO peripheral or from software controlled SIO
static void scsidma_config_gpio()
{
    if (g_scsi_dma_state == SCSIDMA_IDLE)
    {
        iobank0_hw->io[SCSI_IO_DB0].ctrl  = GPIO_FUNC_SIO;
        iobank0_hw->io[SCSI_IO_DB1].ctrl  = GPIO_FUNC_SIO;
        iobank0_hw->io[SCSI_IO_DB2].ctrl  = GPIO_FUNC_SIO;
        iobank0_hw->io[SCSI_IO_DB3].ctrl  = GPIO_FUNC_SIO;
        iobank0_hw->io[SCSI_IO_DB4].ctrl  = GPIO_FUNC_SIO;
        iobank0_hw->io[SCSI_IO_DB5].ctrl  = GPIO_FUNC_SIO;
        iobank0_hw->io[SCSI_IO_DB6].ctrl  = GPIO_FUNC_SIO;
        iobank0_hw->io[SCSI_IO_DB7].ctrl  = GPIO_FUNC_SIO;
        iobank0_hw->io[SCSI_IO_DBP].ctrl  = GPIO_FUNC_SIO;
        iobank0_hw->io[SCSI_OUT_REQ].ctrl = GPIO_FUNC_SIO;
    }
    else if (g_scsi_dma_state == SCSIDMA_WRITE)
    {
        // Make sure the initial state of all pins is high and output
        pio_sm_set_pins(SCSI_DMA_PIO, SCSI_DMA_SM, 0x3FF);
        pio_sm_set_consecutive_pindirs(SCSI_DMA_PIO, SCSI_DMA_SM, 0, 10, true);

        iobank0_hw->io[SCSI_IO_DB0].ctrl  = GPIO_FUNC_PIO0;
        iobank0_hw->io[SCSI_IO_DB1].ctrl  = GPIO_FUNC_PIO0;
        iobank0_hw->io[SCSI_IO_DB2].ctrl  = GPIO_FUNC_PIO0;
        iobank0_hw->io[SCSI_IO_DB3].ctrl  = GPIO_FUNC_PIO0;
        iobank0_hw->io[SCSI_IO_DB4].ctrl  = GPIO_FUNC_PIO0;
        iobank0_hw->io[SCSI_IO_DB5].ctrl  = GPIO_FUNC_PIO0;
        iobank0_hw->io[SCSI_IO_DB6].ctrl  = GPIO_FUNC_PIO0;
        iobank0_hw->io[SCSI_IO_DB7].ctrl  = GPIO_FUNC_PIO0;
        iobank0_hw->io[SCSI_IO_DBP].ctrl  = GPIO_FUNC_PIO0;
        iobank0_hw->io[SCSI_OUT_REQ].ctrl = GPIO_FUNC_PIO0;
    }
    else if (g_scsi_dma_state == SCSIDMA_READ)
    {
        // Data bus as input, REQ pin as output
        pio_sm_set_pins(SCSI_DMA_PIO, SCSI_DMA_SM, 0x3FF);
        pio_sm_set_consecutive_pindirs(SCSI_DMA_PIO, SCSI_DMA_SM, 0, 9, false);
        pio_sm_set_consecutive_pindirs(SCSI_DMA_PIO, SCSI_DMA_SM, 9, 1, true);

        iobank0_hw->io[SCSI_IO_DB0].ctrl  = GPIO_FUNC_SIO;
        iobank0_hw->io[SCSI_IO_DB1].ctrl  = GPIO_FUNC_SIO;
        iobank0_hw->io[SCSI_IO_DB2].ctrl  = GPIO_FUNC_SIO;
        iobank0_hw->io[SCSI_IO_DB3].ctrl  = GPIO_FUNC_SIO;
        iobank0_hw->io[SCSI_IO_DB4].ctrl  = GPIO_FUNC_SIO;
        iobank0_hw->io[SCSI_IO_DB5].ctrl  = GPIO_FUNC_SIO;
        iobank0_hw->io[SCSI_IO_DB6].ctrl  = GPIO_FUNC_SIO;
        iobank0_hw->io[SCSI_IO_DB7].ctrl  = GPIO_FUNC_SIO;
        iobank0_hw->io[SCSI_IO_DBP].ctrl  = GPIO_FUNC_SIO;
        iobank0_hw->io[SCSI_OUT_REQ].ctrl = GPIO_FUNC_PIO0;
    }
}

static void start_dma_write()
{
    // Prefill both DMA buffers
    g_scsi_dma.dma_countA = refill_dmabuf(g_scsi_dma.dma_bufA);
    g_scsi_dma.dma_countB = refill_dmabuf(g_scsi_dma.dma_bufB);
    
    if (g_scsi_dma.syncOffset == 0)
    {
        // Asynchronous mode
        // Start DMA from buffer A
        g_scsi_dma.dma_current_buf = SCSIBUF_A;
        dma_channel_configure(SCSI_DMA_CH,
            &g_scsi_dma.dma_write_config,
            &SCSI_DMA_PIO->txf[SCSI_DMA_SM],
            g_scsi_dma.dma_bufA,
            g_scsi_dma.dma_countA,
            true
        );

        // Enable state machine
        pio_sm_set_enabled(SCSI_DMA_PIO, SCSI_DMA_SM, true);
    }
    else
    {
        // Synchronous mode

        // Start DMA transfer to move dummy bits to write pacer
        dma_channel_configure(SCSI_DMA_SYNC_CH,
            &g_scsi_dma.dma_write_pacer_config,
            &SCSI_DMA_PIO->txf[SCSI_DMA_SYNC_CH],
            &SCSI_DMA_PIO->rxf[SCSI_DMA_SM],
            0xFFFFFFFF,
            true
        );

        // Start DMA transfer to move data from buffer A to data writer
        g_scsi_dma.dma_current_buf = SCSIBUF_A;
        dma_channel_configure(SCSI_DMA_CH,
            &g_scsi_dma.dma_write_config,
            &SCSI_DMA_PIO->txf[SCSI_DMA_SM],
            g_scsi_dma.dma_bufA,
            g_scsi_dma.dma_countA,
            true
        );

        // Enable state machines
        pio_sm_set_enabled(SCSI_DMA_PIO, SCSI_DMA_SYNC_SM, true);
        pio_sm_set_enabled(SCSI_DMA_PIO, SCSI_DMA_SM, true);
    }

}

static void scsi_dma_write_irq()
{
    dma_hw->ints0 = 1 << SCSI_DMA_CH;

    if (g_scsi_dma.dma_current_buf == SCSIBUF_A)
    {
        // Transfer from buffer A finished
        g_scsi_dma.dma_countA = 0;
        g_scsi_dma.dma_current_buf = SCSIBUF_NONE;

        if (g_scsi_dma.dma_countB != 0)
        {
            // Start transferring buffer B immediately
            dma_channel_set_trans_count(SCSI_DMA_CH, g_scsi_dma.dma_countB, false);
            dma_channel_set_read_addr(SCSI_DMA_CH, g_scsi_dma.dma_bufB, true);
            g_scsi_dma.dma_current_buf = SCSIBUF_B;

            // Refill buffer A for next time
            g_scsi_dma.dma_countA = refill_dmabuf(g_scsi_dma.dma_bufA);
        }
    }
    else
    {
        // Transfer from buffer B finished
        g_scsi_dma.dma_countB = 0;
        g_scsi_dma.dma_current_buf = SCSIBUF_NONE;

        if (g_scsi_dma.dma_countA != 0)
        {
            // Start transferring buffer A immediately
            dma_channel_set_trans_count(SCSI_DMA_CH, g_scsi_dma.dma_countA, false);
            dma_channel_set_read_addr(SCSI_DMA_CH, g_scsi_dma.dma_bufA, true);
            g_scsi_dma.dma_current_buf = SCSIBUF_A;

            // Refill buffer B for next time
            g_scsi_dma.dma_countB = refill_dmabuf(g_scsi_dma.dma_bufB);
        }
    }

    if (g_scsi_dma.dma_current_buf == SCSIBUF_NONE)
    {
        // Both buffers are empty, check if we have more data
        g_scsi_dma.dma_countA = refill_dmabuf(g_scsi_dma.dma_bufA);

        if (g_scsi_dma.dma_countA == 0)
        {
            // End of data for DMA, but PIO may still have bytes in its buffer
            g_scsi_dma_state = SCSIDMA_WRITE_DONE;
        }
        else
        {
            // Start transfer from buffer A
            dma_channel_set_trans_count(SCSI_DMA_CH, g_scsi_dma.dma_countA, false);
            dma_channel_set_read_addr(SCSI_DMA_CH, g_scsi_dma.dma_bufA, true);
            g_scsi_dma.dma_current_buf = SCSIBUF_A;

            // Refill B for the next interrupt
            g_scsi_dma.dma_countB = refill_dmabuf(g_scsi_dma.dma_bufB);
        }
    }
}

void scsi_accel_rp2040_startWrite(const uint8_t* data, uint32_t count, volatile int *resetFlag)
{
    // Number of bytes should always be divisible by 2.
    assert((count & 1) == 0);

    __disable_irq();
    if (g_scsi_dma_state == SCSIDMA_WRITE)
    {
        if (!g_scsi_dma.next_app_buf && data == g_scsi_dma.app_buf + g_scsi_dma.app_bytes)
        {
            // Combine with currently running request
            g_scsi_dma.app_bytes += count;
            count = 0;
        }
        else if (data == g_scsi_dma.next_app_buf + g_scsi_dma.next_app_bytes)
        {
            // Combine with queued request
            g_scsi_dma.next_app_bytes += count;
            count = 0;
        }
        else if (!g_scsi_dma.next_app_buf)
        {
            // Add as queued request
            g_scsi_dma.next_app_buf = (uint8_t*)data;
            g_scsi_dma.next_app_bytes = count;
            count = 0;
        }
    }
    __enable_irq();

    // Check if the request was combined
    if (count == 0) return;

    if (g_scsi_dma_state != SCSIDMA_IDLE && g_scsi_dma_state != SCSIDMA_WRITE_DONE)
    {
        // Wait for previous request to finish
        scsi_accel_rp2040_finishWrite(resetFlag);
        if (*resetFlag)
        {
            return;
        }
    }

    bool must_reconfig_gpio = (g_scsi_dma_state == SCSIDMA_IDLE);
    g_scsi_dma_state = SCSIDMA_WRITE;
    g_scsi_dma.app_buf = (uint8_t*)data;
    g_scsi_dma.app_bytes = count;
    g_scsi_dma.dma_bytes = 0;
    g_scsi_dma.next_app_buf = 0;
    g_scsi_dma.next_app_bytes = 0;
    g_scsi_dma.dma_current_buf = SCSIBUF_NONE;
    
    if (must_reconfig_gpio)
    {
        SCSI_ENABLE_DATA_OUT();

        if (g_scsi_dma.syncOffset == 0)
        {
            // Asynchronous write
            pio_sm_init(SCSI_DMA_PIO, SCSI_DMA_SM, g_scsi_dma.pio_offset_async_write, &g_scsi_dma.pio_cfg_async_write);
            scsidma_config_gpio();
        }
        else
        {
            // Synchronous write
            // First state machine writes data to SCSI bus and dummy bits to its RX fifo.
            // Second state machine empties the dummy bits every time ACK is received, to control the transmit pace.
            pio_sm_init(SCSI_DMA_PIO, SCSI_DMA_SM, g_scsi_dma.pio_offset_sync_write, &g_scsi_dma.pio_cfg_sync_write);
            pio_sm_init(SCSI_DMA_PIO, SCSI_DMA_SYNC_SM, g_scsi_dma.pio_offset_sync_write_pacer, &g_scsi_dma.pio_cfg_sync_write_pacer);
            scsidma_config_gpio();

            // Prefill RX fifo to set the syncOffset
            for (int i = 0; i < g_scsi_dma.syncOffsetPreload; i++)
            {
                pio_sm_exec(SCSI_DMA_PIO, SCSI_DMA_SM,
                    pio_encode_push(false, false) | pio_encode_sideset(1, 1));
            }

            // Fill the pacer TX fifo
            // DMA should start transferring only after ACK pulses are received
            for (int i = 0; i < 4; i++)
            {
                pio_sm_put(SCSI_DMA_PIO, SCSI_DMA_SYNC_SM, 0);
            }

            // Fill the pacer OSR
            pio_sm_exec(SCSI_DMA_PIO, SCSI_DMA_SYNC_SM,
                pio_encode_mov(pio_osr, pio_null));
        }
        
        dma_channel_set_irq0_enabled(SCSI_DMA_CH, true);
        irq_set_exclusive_handler(DMA_IRQ_0, scsi_dma_write_irq);
        irq_set_enabled(DMA_IRQ_0, true);
    }

    start_dma_write();
}

bool scsi_accel_rp2040_isWriteFinished(const uint8_t* data)
{
    // Check if everything has completed
    if (g_scsi_dma_state == SCSIDMA_IDLE || g_scsi_dma_state == SCSIDMA_WRITE_DONE)
    {
        return true;
    }

    if (!data)
        return false;
    
    // Check if this data item is still in queue.
    __disable_irq();
    bool finished = true;
    if (data >= g_scsi_dma.app_buf + g_scsi_dma.dma_bytes &&
        data < g_scsi_dma.app_buf + g_scsi_dma.app_bytes)
    {
        finished = false; // In current transfer
    }
    else if (data >= g_scsi_dma.next_app_buf &&
             data < g_scsi_dma.next_app_buf + g_scsi_dma.next_app_bytes)
    {
        finished = false; // In queued transfer
    }
    __enable_irq();

    return finished;
}

void scsi_accel_rp2040_stopWrite(volatile int *resetFlag)
{
    // Wait for TX fifo to be empty and ACK to go high
    // For synchronous writes wait for all ACKs to be received also
    uint32_t start = millis();
    while ((!pio_sm_is_tx_fifo_empty(SCSI_DMA_PIO, SCSI_DMA_SM)
            || pio_sm_get_rx_fifo_level(SCSI_DMA_PIO, SCSI_DMA_SM) > g_scsi_dma.syncOffsetPreload
            || SCSI_IN(ACK)) && !*resetFlag)
    {
        if ((uint32_t)(millis() - start) > 5000)
        {
            azlog("scsi_accel_rp2040_stopWrite() timeout, FIFO levels ",
                (int)pio_sm_get_tx_fifo_level(SCSI_DMA_PIO, SCSI_DMA_SM), " ",
                (int)pio_sm_get_rx_fifo_level(SCSI_DMA_PIO, SCSI_DMA_SM));
            *resetFlag = 1;
            break;
        }
    }

    dma_channel_abort(SCSI_DMA_CH);
    dma_channel_abort(SCSI_DMA_SYNC_CH);
    dma_channel_set_irq0_enabled(SCSI_DMA_CH, false);
    g_scsi_dma_state = SCSIDMA_IDLE;
    SCSI_RELEASE_DATA_REQ();
    scsidma_config_gpio();
    pio_sm_set_enabled(SCSI_DMA_PIO, SCSI_DMA_SM, false);
    pio_sm_set_enabled(SCSI_DMA_PIO, SCSI_DMA_SYNC_SM, false);
}

void scsi_accel_rp2040_finishWrite(volatile int *resetFlag)
{
    uint32_t start = millis();
    while (g_scsi_dma_state != SCSIDMA_IDLE && !*resetFlag)
    {
        if ((uint32_t)(millis() - start) > 5000)
        {
            azlog("scsi_accel_rp2040_finishWrite() timeout,"
             " state: ", (int)g_scsi_dma_state, " ", (int)g_scsi_dma.dma_current_buf, " ", (int)g_scsi_dma.dma_countA, " ", (int)g_scsi_dma.dma_countB,
             " PIO PC: ", (int)pio_sm_get_pc(SCSI_DMA_PIO, SCSI_DMA_SM), " ", (int)pio_sm_get_pc(SCSI_DMA_PIO, SCSI_DMA_SYNC_SM),
             " PIO FIFO: ", (int)pio_sm_get_tx_fifo_level(SCSI_DMA_PIO, SCSI_DMA_SM), " ", (int)pio_sm_get_tx_fifo_level(SCSI_DMA_PIO, SCSI_DMA_SYNC_SM),
             " DMA counts: ", dma_hw->ch[SCSI_DMA_CH].al2_transfer_count, " ", dma_hw->ch[SCSI_DMA_SYNC_CH].al2_transfer_count);
            *resetFlag = 1;
            break;
        }

        if (g_scsi_dma_state == SCSIDMA_WRITE_DONE)
        {
            // DMA done, wait for PIO to finish also and reconfig GPIO.
            scsi_accel_rp2040_stopWrite(resetFlag);
        }
    }
}

void scsi_accel_rp2040_read(uint8_t *buf, uint32_t count, int *parityError, volatile int *resetFlag)
{
    // The hardware would support DMA for reading from SCSI bus also, but currently
    // the rest of the software architecture does not. There is not much benefit
    // because there isn't much else to do before we get the data from the SCSI bus.
    //
    // Currently this method just reads from the PIO RX fifo directly in software loop.
    
    g_scsi_dma_state = SCSIDMA_READ;
    pio_sm_init(SCSI_DMA_PIO, SCSI_DMA_SM, g_scsi_dma.pio_offset_async_read, &g_scsi_dma.pio_cfg_async_read);
    scsidma_config_gpio();
    pio_sm_set_enabled(SCSI_DMA_PIO, SCSI_DMA_SM, true);

    // Set the number of bytes to read, must be divisible by 2.
    assert((count & 1) == 0);
    pio_sm_put(SCSI_DMA_PIO, SCSI_DMA_SM, count - 1);

    // Read results from PIO RX FIFO
    uint8_t *dst = buf;
    uint8_t *end = buf + count;
    uint32_t paritycheck = 0;
    while (dst < end)
    {
        if (*resetFlag)
        {
            break;
        }

        uint32_t available = pio_sm_get_rx_fifo_level(SCSI_DMA_PIO, SCSI_DMA_SM);

        while (available > 0)
        {
            available--;
            uint32_t word = pio_sm_get(SCSI_DMA_PIO, SCSI_DMA_SM);
            paritycheck ^= word;
            word = ~word;
            *dst++ = word & 0xFF;
            *dst++ = word >> 16;
        }
    }

    // Check parity errors in whole block
    // This doesn't detect if there is even number of parity errors in block.
    uint8_t byte0 = ~(paritycheck & 0xFF);
    uint8_t byte1 = ~(paritycheck >> 16);
    if (paritycheck != ((g_scsi_parity_lookup[byte1] << 16) | g_scsi_parity_lookup[byte0]))
    {
        azlog("Parity error in scsi_accel_rp2040_read(): ", paritycheck);
        *parityError = 1;
    }

    g_scsi_dma_state = SCSIDMA_IDLE;
    SCSI_RELEASE_DATA_REQ();
    scsidma_config_gpio();
    pio_sm_set_enabled(SCSI_DMA_PIO, SCSI_DMA_SM, false);
}

void scsi_accel_rp2040_init()
{
    g_scsi_dma_state = SCSIDMA_IDLE;
    scsidma_config_gpio();

    // Mark channels as being in use, unless it has been done already
    if (!g_channels_claimed)
    {
        pio_sm_claim(SCSI_DMA_PIO, SCSI_DMA_SM);
        dma_channel_claim(SCSI_DMA_CH);
        g_channels_claimed = true;
    }

    // Load PIO programs
    pio_clear_instruction_memory(SCSI_DMA_PIO);
    
    // Asynchronous SCSI write
    g_scsi_dma.pio_offset_async_write = pio_add_program(SCSI_DMA_PIO, &scsi_accel_async_write_program);
    g_scsi_dma.pio_cfg_async_write = scsi_accel_async_write_program_get_default_config(g_scsi_dma.pio_offset_async_write);
    sm_config_set_out_pins(&g_scsi_dma.pio_cfg_async_write, SCSI_IO_DB0, 9);
    sm_config_set_sideset_pins(&g_scsi_dma.pio_cfg_async_write, SCSI_OUT_REQ);
    sm_config_set_fifo_join(&g_scsi_dma.pio_cfg_async_write, PIO_FIFO_JOIN_TX);
    sm_config_set_out_shift(&g_scsi_dma.pio_cfg_async_write, true, false, 32);

    // Asynchronous / synchronous SCSI read
    g_scsi_dma.pio_offset_async_read = pio_add_program(SCSI_DMA_PIO, &scsi_accel_async_read_program);
    g_scsi_dma.pio_cfg_async_read = scsi_accel_async_read_program_get_default_config(g_scsi_dma.pio_offset_async_read);
    sm_config_set_in_pins(&g_scsi_dma.pio_cfg_async_read, SCSI_IO_DB0);
    sm_config_set_sideset_pins(&g_scsi_dma.pio_cfg_async_read, SCSI_OUT_REQ);
    sm_config_set_out_shift(&g_scsi_dma.pio_cfg_async_read, true, false, 32);
    sm_config_set_in_shift(&g_scsi_dma.pio_cfg_async_read, true, true, 32);

    // Synchronous SCSI write pacer / ACK handler
    g_scsi_dma.pio_offset_sync_write_pacer = pio_add_program(SCSI_DMA_PIO, &scsi_sync_write_pacer_program);
    g_scsi_dma.pio_cfg_sync_write_pacer = scsi_sync_write_pacer_program_get_default_config(g_scsi_dma.pio_offset_sync_write_pacer);
    sm_config_set_out_shift(&g_scsi_dma.pio_cfg_sync_write_pacer, true, true, 1);

    // Synchronous SCSI data writer
    g_scsi_dma.pio_offset_sync_write = pio_add_program(SCSI_DMA_PIO, &scsi_sync_write_program);
    g_scsi_dma.pio_cfg_sync_write = scsi_sync_write_program_get_default_config(g_scsi_dma.pio_offset_sync_write);
    sm_config_set_out_pins(&g_scsi_dma.pio_cfg_sync_write, SCSI_IO_DB0, 9);
    sm_config_set_sideset_pins(&g_scsi_dma.pio_cfg_sync_write, SCSI_OUT_REQ);
    sm_config_set_out_shift(&g_scsi_dma.pio_cfg_sync_write, true, true, 32);
    sm_config_set_in_shift(&g_scsi_dma.pio_cfg_sync_write, true, true, 1);

    // Create DMA channel configuration so it can be applied quickly later
    dma_channel_config cfg = dma_channel_get_default_config(SCSI_DMA_CH);
    channel_config_set_transfer_data_size(&cfg, DMA_SIZE_32);
    channel_config_set_read_increment(&cfg, true);
    channel_config_set_write_increment(&cfg, false);
    channel_config_set_dreq(&cfg, pio_get_dreq(SCSI_DMA_PIO, SCSI_DMA_SM, true));
    g_scsi_dma.dma_write_config = cfg;

    // In synchronous mode a second DMA channel is used to transfer dummy bits
    // from first state machine to second one.
    cfg = dma_channel_get_default_config(SCSI_DMA_SYNC_CH);
    channel_config_set_transfer_data_size(&cfg, DMA_SIZE_32);
    channel_config_set_read_increment(&cfg, false);
    channel_config_set_write_increment(&cfg, false);
    channel_config_set_dreq(&cfg, pio_get_dreq(SCSI_DMA_PIO, SCSI_DMA_SYNC_SM, true));
    g_scsi_dma.dma_write_pacer_config = cfg;
}

void scsi_accel_rp2040_setWriteMode(int syncOffset, int syncPeriod)
{
    if (syncOffset != g_scsi_dma.syncOffset || syncPeriod != g_scsi_dma.syncPeriod)
    {
        g_scsi_dma.syncOffset = syncOffset;
        g_scsi_dma.syncPeriod = syncPeriod;

        if (syncOffset > 0)
        {
            // Set up offset amount to PIO state machine configs.
            // The RX fifo of scsi_sync_write has 4 slots.
            // We can preload it with 0-3 items and set the autopush threshold 1, 2, 4 ... 32
            // to act as a divider. This allows offsets 1 to 128 bytes.
            // SCSI2SD code currently only uses offsets up to 15.
            if (syncOffset <= 4)
            {
                g_scsi_dma.syncOffsetDivider = 1;
                g_scsi_dma.syncOffsetPreload = 5 - syncOffset;
            }
            else if (syncOffset <= 8)
            {
                g_scsi_dma.syncOffsetDivider = 2;
                g_scsi_dma.syncOffsetPreload = 5 - syncOffset / 2;
            }
            else if (syncOffset <= 16)
            {
                g_scsi_dma.syncOffsetDivider = 4;
                g_scsi_dma.syncOffsetPreload = 5 - syncOffset / 4;
            }
            else
            {
                g_scsi_dma.syncOffsetDivider = 4;
                g_scsi_dma.syncOffsetPreload = 0;
            }

            // To properly detect when all bytes have been ACKed,
            // we need at least one vacant slot in the FIFO.
            if (g_scsi_dma.syncOffsetPreload > 3)
                g_scsi_dma.syncOffsetPreload = 3;

            sm_config_set_out_shift(&g_scsi_dma.pio_cfg_sync_write_pacer, true, true, g_scsi_dma.syncOffsetDivider);
            sm_config_set_in_shift(&g_scsi_dma.pio_cfg_sync_write, true, true, g_scsi_dma.syncOffsetDivider);

            // Set up the timing parameters to PIO program
            // The scsi_sync_write PIO program consists of three instructions.
            // The delays are in clock cycles, each taking 8 ns.
            // delay0: Delay from data write to REQ assertion
            // delay1: Delay from REQ assert to REQ deassert
            // delay2: Delay from REQ deassert to data write
            int delay0, delay1, delay2;
            int totalDelay = syncPeriod * 4 / 8;

            if (syncPeriod <= 25)
            {
                // Fast SCSI timing: 30 ns assertion period, 25 ns skew delay
                // The hardware rise and fall time require some extra delay,
                // the values below are tuned based on oscilloscope measurements.
                delay0 = 3;
                delay1 = 5;
                delay2 = totalDelay - delay0 - delay1 - 3;
                if (delay2 < 0) delay2 = 0;
                if (delay2 > 15) delay2 = 15;
            }
            else
            {
                // Slow SCSI timing: 90 ns assertion period, 55 ns skew delay
                delay0 = 6;
                delay1 = 12;
                delay2 = totalDelay - delay0 - delay1 - 3;
                if (delay2 < 0) delay2 = 0;
                if (delay2 > 15) delay2 = 15;
            }

            // Patch the delay values into the instructions.
            // The code in scsi_accel.pio must have delay set to 0 for this to work correctly.
            uint16_t instr0 = scsi_sync_write_program_instructions[0] | pio_encode_delay(delay0);
            uint16_t instr1 = scsi_sync_write_program_instructions[1] | pio_encode_delay(delay1);
            uint16_t instr2 = scsi_sync_write_program_instructions[2] | pio_encode_delay(delay2);

            SCSI_DMA_PIO->instr_mem[g_scsi_dma.pio_offset_sync_write + 0] = instr0;
            SCSI_DMA_PIO->instr_mem[g_scsi_dma.pio_offset_sync_write + 1] = instr1;
            SCSI_DMA_PIO->instr_mem[g_scsi_dma.pio_offset_sync_write + 2] = instr2;
        }
    }

}