Differences

This shows you the differences between two versions of the page.

--- boards:ecb:usb-fifo:start [2017/03/20 04:34]
will [Notes on Construction]
+++ boards:ecb:usb-fifo:start [2017/03/26 16:59]
will [Example Code]
@@ Line 7: / Line 7: @@
 On the PC the interface is presented as a standard USB serial interface (a "Virtual COM port" on Windows, /dev/ttyUSB* on Linux) and can be used by any application normally used with standard serial ports. Note that although it presents as a serial port, the baud rate and other serial settings configured on the Virtual COM Port are ignored, it just provides an 8-bit clean path at whatever rate you can pump data in or out of it.
-The FT232H has a separate FIFO (first-in-first-out queue) for the receive and transmit directions. Each FIFO is 1KB in size. In the receive direction (PC to ECB) the operating system decides when to transmit data and can send up to 512 bytes in a single USB transfer. In the transmit direction (ECB to PC) the FT232H will accumulate data until 512 bytes has been received, or some period of time (believed to be around 17ms) has passed since the last byte was queued, or when a "send immediate" signal is given.
+The FT232H has a separate FIFO (first-in-first-out queue) for the receive and transmit directions. Each FIFO is 1KB in size. Data is transferred to/from the FIFOs over the USB link in blocks of up to 512 bytes. A "send immediate" operation is supported which causes any queued data in the transmit FIFO to be sent over the USB link at the earliest opportunity, otherwise the FT232H may wait a short while to accumulate more data before performing a transfer over the USB link.
 The board supports generating interrupts on either (or both) of two conditions: data waiting in receive FIFO, or space available in transmit FIFO. The interrupt can be routed to ECB lines NMI, INT, IR0–IR7. Enabling and masking of interrupts is under software control.
@@ Line 37: / Line 37: @@
 |7 (0x80)|**RX_EMPTY:** read-only \\ 0 if the receive FIFO contains queued data, \\ 1 if the receive FIFO is empty. \\ Any reads from the FIFO while it is empty will return junk values.|
-The **INT_TX** and **INT_RX** bits in the Status Register control the conditions under which an interrupt will be requested. The **IRQ** bit always reflects if either condition is met regardless of the value of **INT_ENABLE**. The bus interrupt line will be asserted only when the **INT_ENABLE** bit is also set. In other words, the bus interrupt line is asserted only when **INT_TX** and/or **INT_RX** are set, one or both of the relevant conditions is met, and **INT_ENABLE** is also set. So, for example, software which wants to receive an interrupt when data arrives in the receive FIFO over USB should set both **INT_RX** and **INT_ENABLE**. If the interrupt line is shared with multiple devices the interrupt service routine can then check the **IRQ** bit to determine if the USB-FIFO card is requesting the interrupt before calling the USB-FIFO interrupt handler code.
+Interrupts: Interrupt requests are controlled in two stages. The first stage is controlled by the **INT_TX** and **INT_RX** bits in the Status Register. Setting these bits to 1 causes an interrupt to be requested when the transmit FIFO has space available (**INT_TX**), or the receive FIFO contains data (**INT_RX**). The **IRQ** bit in the Status Register will be 1 only when either of these bits is set and the corresponding condition arises. The second stage is the **INT_ENABLE** bit: When the **INT_ENABLE** bit in the Status Register is set, and the **IRQ** bit is 1, the bus interrupt line selected with jumper **J3** will be asserted to interrupt the CPU.
-When the USB cable is disconnected, **TX_FULL** =1 and **RX_EMPTY** =1 indicating (correctly!) that data cannot be transferred in either direction.
+For example, software which wants to receive an interrupt when data arrives in the receive FIFO over USB should set both **INT_RX** and **INT_ENABLE**. If the interrupt line is shared with multiple devices the interrupt service routine can then check the **IRQ** bit to determine if the USB-FIFO card is requesting the interrupt before calling the USB-FIFO interrupt handler code.
-When the ECB machine is reset, the **INT_ENABLE**, **INT_TX**, **INT_RX** and **GPIO_IN** bits are all reset to 0. The USB connection is **not** reset (ie the virtual serial device will remain connected).
+When the USB cable is disconnected, **TX_FULL** and **RX_EMPTY** will both be set, indicating that data cannot be transferred in either direction.
+When the ECB machine is reset, the **INT_ENABLE**, **INT_TX**, **INT_RX** and **GPIO_IN** bits are all reset to 0. The USB connection is **not** reset (ie the virtual serial device will remain connected).
 ===== ECB Card Jumpers =====
@@ Line 66: / Line 67: @@
 |J2|2×6 0.1" header|TE Connectivity part 5-826632-0: 2×50 contact breakaway header strip (Farnell order code 3418560)|
 |J3|2×10 0.1" header|TE Connectivity part 5-826632-0: 2×50 contact breakaway header strip (Farnell order code 3418560)|
-|U1, U3, U9|74LS244|TI SN74LS244N (Farnell order code 1739688)|
+|U1, U3|74LS244|TI SN74LS244N (Farnell order code 1739688)|
+|U9|74AHCT244 (preferred) or 74LS244|TI SN74AHCT244N (Farnell order code 1752769)|
 |U2|74LS245|TI SN74LS245N (Farnell order code 1106085)|
 |U4|74LS688|TI SN74LS688N (Farnell order code 1470949)|
 |U5|74LS38|TI SN74LS38N (Farnell order code 1470758)|
-|U6|74LS139A|TI SN74LS139AN (Farnell order code 9592296)|
+|U6|74AHCT139 (preferred) or 74LS139A|TI SN74AHCT139N (Farnell order code 1741539)|
-|U7, U11|74LS32|TI SN74LS32N (Farnell order code 1740030)|
+|U7, U11|74ACT32 (preferred), 74AHCT32 (untested but should work) or 74LS32|TI SN74ACT32N (Farnell order code 1739969), TI SN74AHCT32N (Farnell order code 1749941) or TI SN74LS32N (Farnell order code 1740030)|
 |U8|74LS175|TI SN74LS175N (Farnell order code 1607731)|
 |U10|Adafruit FT232H Breakout (product 2264)|Mouser order code 485-2264, Digikey order code 1528-1449-ND|
@@ Line 78: / Line 80: @@
 |(qty 2)|16 pin DIP IC socket|TE Connectivity 1-2199298-4 (Farnell order code 2445622)|
 |(qty 3)|14 pin DIP IC socket|TE Connectivity 1-2199298-3 (Farnell order code 2445621)|
+\\
 ===== Notes on Construction =====
@@ Line 93: / Line 98: @@
 **For Linux** I have written a {{:boards:ecb:usb-fifo:ft232h-program-eeprom.tar.gz|short C program }}  which uses libftdi1 to program the EEPROM. The tarball contains both the source code and a binary with libftdi1 and libusb statically linked in, this should work on most recent Linux systems which use (the dreaded) systemd. Ensure the FT232H board is the only connected FTDI device (just in case it tries to overwrite the EEPROM in other devices!) and then run "sudo ./program-eeprom -w" to program the device. Running "sudo ./program-eeprom" (without the "-w" option) will report the current EEPROM contents.
-**For MacOS** I had success running FT_PROG in a virtual Windows machine (using Parallels Desktop) using the USB passthrough feature.
+**For MacOS** I had success running FT_PROG in a virtual Windows machine (using Parallels Desktop) using the USB passthrough feature. In principle it should also be possible to compile libusb, libftdi1 and use my C program to program the EEPROM but I have not tested this.
-It is recommended to use 74LS series parts on this board, at the time of writing it has not been tested with substitutions from other 74 series logic families. In particular U1, U2 and U3 benefit from having hysteresis (Schmitt triggers) on the inputs, which the 74LS244 and 74LS245 parts have.
+It is possible to build this board with entirely 74LS series logic, and this works well. However slightly higher performance can be achieved by substituting 74AHCT parts for U6 and U9, and 74ACT for U7 and U11. Testing on a Mark IV SBC at 36.864MHz, a board using only 74LS parts requires 2 I/O wait states, whereas with the 74AHCT parts at U6 and U9 the board operates correctly with only 1 I/O wait state. U7 and U11 can use 74ACT32 which also gives a further timing improvement. The [[https://www.retrobrewcomputers.org/forum/index.php?t=msg&th=142&goto=2061&#msg_2061|forum thread]] has more information on how the timing improves with CMOS parts. Note that U1, U2 and U3 should always use 74LS as the bus interface benefits from having hysteresis on the inputs to improve noise rejection; the 74LS244 and 74LS245 parts have Schmitt trigger inputs.
@@ Line 156: / Line 161: @@
 </code>
-Untested idea: For writes up to 512 bytes in length, I believe you could signal a Send Immediate, then poll for the RX_EMPTY bit, and then proceed to load up to 512 bytes into the transmit FIFO without checking the RX_EMPTY bit again (using the OTIR instruction, or an unrolled loop of OUTIs). I believe the 1KB FIFO in the FT232H is divided into two 512-byte buffers and one is loaded with data while the other is transferred over USB, so once any space in the buffer becomes available you can be confident there is at least 512 bytes of space available. Again, this is untested, but could allow for very fast transmission.
+I also have a file transfer application for CP/M, FIFOPIPE. Drop me an email (will /at/ sowerbutts.com) if you'd like to try it out.
-\\