From 5f06db87871e892efb97ad1ac5f72aaf7e164f29 Mon Sep 17 00:00:00 2001
From: mwojcik <mw@m-labs.hk>
Date: Thu, 30 Sep 2021 13:32:19 +0200
Subject: [PATCH] drtio: swap byte order, add work buffer, comm ok

---
 src/libboard_artiq/src/drtioaux.rs | 40 ++++++++++++++++++++++++------
 1 file changed, 33 insertions(+), 7 deletions(-)

diff --git a/src/libboard_artiq/src/drtioaux.rs b/src/libboard_artiq/src/drtioaux.rs
index e13bde1..c59c851 100644
--- a/src/libboard_artiq/src/drtioaux.rs
+++ b/src/libboard_artiq/src/drtioaux.rs
@@ -1,4 +1,3 @@
-use core::slice;
 use crc;
 
 use core_io::{ErrorKind as IoErrorKind, Error as IoError};
@@ -59,15 +58,35 @@ fn has_rx_error(linkno: u8) -> bool {
     }
 }
 
+fn swap_byte_order(buf: &mut [u8]) -> () {
+    // for some reason, everything except checksum arrives
+    // with byte order swapped. and it must be sent as such too.
+    // call this for a slice without the checksum included.
+    for i in (0..buf.len()).step_by(4) {
+        let mut temp = buf[i];
+        buf[i] = buf[i + 3];
+        buf[i + 3] = temp;
+        temp = buf[i + 1];
+        buf[i + 1] = buf[i + 2];
+        buf[i + 2] = temp; 
+    }
+}
+
 fn receive<F, T>(linkno: u8, f: F) -> Result<Option<T>, Error>
     where F: FnOnce(&[u8]) -> Result<T, Error>
 {
     let linkidx = linkno as usize;
     unsafe {
         if (DRTIOAUX[linkidx].aux_rx_present_read)() == 1 {
-            let ptr = DRTIOAUX_MEM[linkidx].base + DRTIOAUX_MEM[linkidx].size / 2;
-            let len = (DRTIOAUX[linkidx].aux_rx_length_read)();
-            let result = f(slice::from_raw_parts(ptr as *mut u8, len as usize));
+            let ptr = (DRTIOAUX_MEM[linkidx].base + DRTIOAUX_MEM[linkidx].size / 2) as *mut u8;
+            let len = (DRTIOAUX[linkidx].aux_rx_length_read)() as usize;
+            // work buffer, as byte order will need to be swapped, cannot be in place
+            let mut buf: [u8; 1024] = [0; 1024];
+            for i in 0..len {
+                buf[i] = *(ptr as *mut u8).offset(i as isize);
+            }
+            swap_byte_order(&mut buf[0..len-4]);
+            let result = f(&buf[0..len]);
             (DRTIOAUX[linkidx].aux_rx_present_write)(1);
             Ok(Some(result?))
         } else {
@@ -120,9 +139,14 @@ fn transmit<F>(linkno: u8, f: F) -> Result<(), Error>
     let linkno = linkno as usize;
     unsafe {
         while (DRTIOAUX[linkno].aux_tx_read)() != 0 {}
-        let ptr = DRTIOAUX_MEM[linkno].base;
+        let pointer = DRTIOAUX_MEM[linkno].base as *mut u8;
         let len = DRTIOAUX_MEM[linkno].size / 2;
-        let len = f(slice::from_raw_parts_mut(ptr as *mut u8, len))?;
+        // work buffer, works with unaligned mem access
+        let mut buf: [u8; 1024] = [0; 1024]; 
+        let len = f(&mut buf[0..len])?;
+        for i in 0..len {
+            *pointer.offset(i as isize) = buf[i];
+        }
         (DRTIOAUX[linkno].aux_tx_length_write)(len as u16);
         (DRTIOAUX[linkno].aux_tx_write)(1);
         Ok(())
@@ -134,7 +158,7 @@ pub fn send(linkno: u8, packet: &Packet) -> Result<(), Error> {
         let mut writer = Cursor::new(buffer);
 
         packet.write_to(&mut writer)?;
-
+        
         let padding = 4 - (writer.position() % 4);
         if padding != 4 {
             for _ in 0..padding {
@@ -143,6 +167,8 @@ pub fn send(linkno: u8, packet: &Packet) -> Result<(), Error> {
         }
 
         let checksum = crc::crc32::checksum_ieee(&writer.get_ref()[0..writer.position()]);
+        let len = writer.position();
+        swap_byte_order(&mut writer.get_mut()[0..len]);
         writer.write_u32(checksum)?;
 
         Ok(writer.position())