diff --git a/README.md b/README.md
index 46aec66..43f51b3 100644
--- a/README.md
+++ b/README.md
@@ -10,6 +10,7 @@ fw for a ch32v203 node w/ w5500 ethernet
   - With a 1s interval it works
   - [Disabling SPI DMA](https://git.hye.su/mira/ch32-node/src/branch/master/src/w5500.c#L62) solves it (just commenting out `reg_wizchip_spiburst_cbfunc`), so it's most likely DMA related?
   - SPI DMA only works with [prescalers](https://git.hye.su/mira/ch32-node/src/branch/master/src/spi_dma.c#L140) 8 and 64?
+  - Also, for some reason it needs a ~50ms delay before configuring w5500 when compiled **with** `-O0`, not needed with `-Os`...
 
 TODO: LA?...
 
diff --git a/platformio.ini b/platformio.ini
index 00dd182..e274320 100644
--- a/platformio.ini
+++ b/platformio.ini
@@ -17,7 +17,8 @@ board = genericCH32V203C8T6
 framework = ch32v003fun
 upload_protocol = wlink # isp, minichlink, wch-link, wlink
 build_unflags = -march=rv32imacxw
-build_flags = -march=rv32imac -Wall -Wextra
+build_flags = -march=rv32imac_zicsr -Wall -Wextra
+debug_build_flags = -O0 -ggdb3 -g3
 
 [env:local]
 platform_packages = 
diff --git a/src/main.c b/src/main.c
index 1e75545..31c50f5 100644
--- a/src/main.c
+++ b/src/main.c
@@ -46,6 +46,8 @@ void message_arrived(MessageData* md) {
 
 int main(void) {
   init_system();
+  Delay_Ms(55);
+  // DEBUG_PRINT("init_system() done\n");
   configure_network();
 
   // TODO: enabling any kind of SysTick IRQ literally causes the socket to hang forever
diff --git a/src/w5500.c b/src/w5500.c
index dff851a..60dabbc 100644
--- a/src/w5500.c
+++ b/src/w5500.c
@@ -59,7 +59,7 @@ void configure_network(void) {
   // Setup chip select and SPI callbacks
   reg_wizchip_cs_cbfunc(spi_select, spi_unselect);
   reg_wizchip_spi_cbfunc(spi_read_byte, spi_write_byte);
-  // reg_wizchip_spiburst_cbfunc(spidma_read_buffer, spidma_write_buffer);
+  reg_wizchip_spiburst_cbfunc(spidma_read_buffer, spidma_write_buffer);
 
   uint8_t rx_tx_buff_sizes[] = {2, 2, 2, 2, 2, 2, 2, 2};
   wizchip_init(rx_tx_buff_sizes, rx_tx_buff_sizes);