{"id":653,"date":"2020-03-05T08:45:56","date_gmt":"2020-03-05T14:45:56","guid":{"rendered":"https:\/\/jacobncalvert.com\/?p=653"},"modified":"2020-03-05T08:45:58","modified_gmt":"2020-03-05T14:45:58","slug":"better-jtag-on-the-cheap-with-the-ft232h","status":"publish","type":"post","link":"https:\/\/jacobncalvert.com\/blog-archive\/2020\/03\/05\/better-jtag-on-the-cheap-with-the-ft232h\/","title":{"rendered":"Better JTAG on the Cheap with the FT232H"},"content":{"rendered":"\n

A couple of weeks ago I wrote a post about using the FTDI FT232R<\/a> as a cheap JTAG debugger. I’ve been using it for a bit now to play with my Raspberry Pi 3B, and now that my code size has grown, the FT232R is just too slow to cut it. <\/p>\n\n\n\n

Here’s a breakdown: on the FT232R, the max speed I can set the adapter to is 3MHz. This has given me a transfer speed (loading via GDB) of around 3KB\/s. Not too bad for small projects of only a few hundred KiB. But now my code size is approaching a ~5 MiB, the debug cycle was way too long… 5MiB @ 3KB\/s = ~28mins to load… not good!<\/p>\n\n\n\n

Still in my pursuit of a cheap JTAG debugger (I mean come on! It’s just a serial protocol!), I did buy something. The Adafruit FT232H breakout<\/a> is exactly what I was looking for. At only $15 with Amazon Prime shipping, I was back to debugging at a reasonable speed in two days. <\/p>\n\n\n\n

The FT232H breakout is about as barebones as it gets. The board breaks out untouched ACBUS0-ACBUS7 and ADBUS0-ADBUS7 to 0.10″ pitch headers. Since the FT232H has a single MPSSE channel, I can use this breakout to get faster JTAG speeds. <\/p>\n\n\n\n

My configuration files from the previous post had to change a little to accommodate. I’ll break it down below in comments in the file because it’s a little bit cryptic. <\/p>\n\n\n

\n#\n# FTDI USB Hi-Speed to MPSSE Breakout from Adafruit\n#\n# This should work for any bare FT232H\n#\n\n# Setup driver type\nadapter driver ftdi\n\n# 30000 kHZ -> 30MHz\nadapter speed 30000\n\n# Using JTAG (also could be SWD)\ntransport select jtag\n\n# Common PID for FT232H\nftdi_vid_pid 0x0403 0x6014\n\n# Set sampling to allow higher clock speed\nftdi_tdo_sample_edge falling\n\n\n# Layout\n# On this breakout, the LEDs are on ACBUS8 and ACBUS9, can't assign them\n# registers are <ACVALUE><ADVALUE> <ACCONFIG><ADCONFIG>\n# so we set 0x0308 to mean only ACBUS nTRST and nSRST, ADBUS3 (TMS) asserted high\n# and we set 0x000B to mean only AC3,AC2,AC0 outputs -> (TMS,TD0, TCK)\nftdi_layout_init 0x0308 0x000b\n\n# Pins\n# pin name      | func. |\n# --------------|-------|\n# ADBUS0        | TCK   |\n# ADBUS1        | TDI   |\n# ADBUS2        | TDO   |\n# ADBUS3        | TMS   |\n# ACBUS0        | nTRST |\n# ACBUS1        | nSRST |\n#---------------|-------|\n\n# When data == oe -> pins are switched from output to input to give\n# the tri state (L, H, Hi-Z) effect \nftdi_layout_signal nTRST -data 0x0100 -oe 0x0100\nftdi_layout_signal nSRST -data 0x0200 -oe 0x0200\n\n<\/pre><\/div>\n\n\n
So now it is as simple as connecting the corresponding pins on this breakout to the RPi3, and running OpenOCD again. <\/p>\n\n\n\n
With the increased throughput of this MPSSE-supported interface, I now get ~587KB\/s. Much better! It only takes ~8s to load my image now. <\/p>\n","protected":false},"excerpt":{"rendered":"
A couple of weeks ago I wrote a post about using the FTDI FT232R as a cheap JTAG debugger. I’ve been using it for a bit now to play with my Raspberry Pi 3B, and now that my code size has grown, the FT232R is just too slow to cut it. Here’s a breakdown: on the FT232R, the max speed I can set the adapter to is 3MHz. This has given me a transfer speed (loading via GDB) of around…<\/p>\n","protected":false},"author":1,"featured_media":654,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[85,72,5,81,73],"tags":[116,115,111,112],"yoast_head":"\nBetter JTAG on the Cheap with the FT232H - Jacob N Calvert<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/jacobncalvert.com\/blog-archive\/2020\/03\/05\/better-jtag-on-the-cheap-with-the-ft232h\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Better JTAG on the Cheap with the FT232H - Jacob N Calvert\" \/>\n<meta property=\"og:description\" content=\"A couple of weeks ago I wrote a post about using the FTDI FT232R as a cheap JTAG debugger. I’ve been using it for a bit now to play with my Raspberry Pi 3B, and now that my code size has grown, the FT232R is just too slow to cut it. Here’s a breakdown: on the FT232R, the max speed I can set the adapter to is 3MHz. 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