From 988b0fbf27cf83138cf29f1670604fe890e65630 Mon Sep 17 00:00:00 2001
From: Joris van Rantwijk <joris@jorisvr.nl>
Date: Sun, 29 Sep 2024 19:37:02 +0200
Subject: [PATCH] Document digital input registers

---
 doc/fpga_firmware.md | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/doc/fpga_firmware.md b/doc/fpga_firmware.md
index 2f6984f..d1a1e1a 100644
--- a/doc/fpga_firmware.md
+++ b/doc/fpga_firmware.md
@@ -265,6 +265,8 @@ The base address 0x43000000 must be added to obtain the absolute address on the
 | 0x00031C | TT_DMA_STATUS     | Status of DMA write stream for timetagger |
 | 0x000320 | TIMETAGGER_EN     | Mask of enabled timetagger channels |
 | 0x000324 | TIMETAGGER_MARK   | Emit marker record in timetagger data |
+| 0x000330 | DIG_SIMULATE      | Simulate digital input |
+| 0x000338 | DIG_SAMPLE        | Current state of digital input signals |
 | 0x000404 | LED_STATE         | Control LEDs |
 
 **Privileged registers**
@@ -781,6 +783,23 @@ Emit marker record in timetagger data.
 |---------|---------------|--------|-------------|
 | 0       |               | WC     | Write '1' to emit a marker record in the timetagger data stream. |
 
+### 0x000330: DIG_SIMULATE
+
+Simulate digital input.
+
+| Bits    | Field name    | Access | Description |
+|---------|---------------|--------|-------------|
+| 3 : 0   | dig_sim_state | RW     | Simulated digital input state. |
+| 8       | dig_sim_en    | RW     | '1' to use simulated digital input, '0' to use real input. |
+
+### 0x000338: DIG_SAMPLE
+
+Current state of digital input signals.
+
+| Bits    | Field name    | Access | Description |
+|---------|---------------|--------|-------------|
+| 3 : 0   | dig_sample    | RO     | Digital input state. |
+
 ### 0x000404: LED_STATE
 
 Control LEDs.