diff --git a/Tiny-RISCV-SoC-for-RFU.md b/Tiny-RISCV-SoC-for-RFU.md
index bd9ec56..cf7c341 100644
--- a/Tiny-RISCV-SoC-for-RFU.md
+++ b/Tiny-RISCV-SoC-for-RFU.md
@@ -6,6 +6,29 @@ Then run zephyr OS on it. ttps://github.com/olofk/serv has the instructions on t
 
 ZephyrOS seems to also include some RSA implementations, so that's useful.
 
+## BUG BUG BUG
+Arrrrgh this cost me hours. There's a bug in the default driver. It doesn't match the default SoC:
+
+```
+diff --git a/zephyr/soc/riscv/servant/soc.h b/zephyr/soc/riscv/servant/soc.h
+index 0780bb5..0b1e97c 100644
+--- a/zephyr/soc/riscv/servant/soc.h
++++ b/zephyr/soc/riscv/servant/soc.h
+@@ -12,9 +12,11 @@
+ 
+ /* Bitbang UART configuration */
+ #define UART_BITBANG_BASE 0x40000000
++//#define UART_BITBANG_BASE 0x80000000
+ 
+ /* Timer configuration */
+-#define SERV_TIMER_BASE   0x80000000
++#define SERV_TIMER_BASE   0x40000000
++//#define SERV_TIMER_BASE   0x80000000
+ #define SERV_TIMER_IRQ    7
+ 
+ /* lib-c hooks required RAM defined variables */
+```
+
 ## Commands
 
 * Build SERVANT for CMOD A7: `fusesoc run --tool=vivado --target=cmod_a7_35t servant`