diff --git a/sbus-to-ztex-gateware-migen/prom_csr.fth b/sbus-to-ztex-gateware-migen/prom_csr.fth
new file mode 100644
index 0000000..31b500c
--- /dev/null
+++ b/sbus-to-ztex-gateware-migen/prom_csr.fth
@@ -0,0 +1,10 @@
+\ auto-generated base regions for CSRs in the PROM
+h# 40000 constant sbusfpga_csraddr_leds
+h# 41000 constant sbusfpga_csraddr_ddrphy
+h# 42000 constant sbusfpga_csraddr_sdram
+h# 80000 constant sbusfpga_regionaddr_usb_host_ctrl
+h# 90000 constant sbusfpga_regionaddr_usb_shared_mem
+h# 0 constant sbusfpga_regionaddr_prom
+h# fc000000 constant sbusfpga_regionaddr_usb_fake_dma
+h# 80000000 constant sbusfpga_regionaddr_main_ram
+h# 40000 constant sbusfpga_regionaddr_csr
diff --git a/sbus-to-ztex-gateware-migen/prom_migen.fth b/sbus-to-ztex-gateware-migen/prom_migen.fth
index 786d0ac..6b9388a 100644
--- a/sbus-to-ztex-gateware-migen/prom_migen.fth
+++ b/sbus-to-ztex-gateware-migen/prom_migen.fth
@@ -43,7 +43,7 @@ new-device
 \ Absolute minimal stuff; name & registers def.
 " generic-ohci" device-name
 
-my-address h# 80000 + my-space h# 1000 reg
+my-address sbusfpga_regionaddr_usb_host_ctrl + my-space h# 1000 reg
 \ we don't support ET or anything non-32bits
 h# 7c xdrint " slave-burst-sizes" attribute
 h# 7c xdrint " burst-sizes" attribute
@@ -58,7 +58,7 @@ my-space   constant my-sbus-space
 : map-in ( adr space size -- virt ) " map-in" $call-parent ;
 : map-out ( virt size -- ) " map-out" $call-parent ;
 
-: map-in-regs ( -- ) my-sbus-address h# 80000 + my-sbus-space h# 1000 map-in is regs-virt ;
+: map-in-regs ( -- ) my-sbus-address sbusfpga_regionaddr_usb_host_ctrl + my-sbus-space h# 1000 map-in is regs-virt ;
 : map-out-regs ( -- ) regs-virt h# 1000 map-out ;
 
 : my-reset! ( -- )